- 5 Essential Tips for Vegetable Gardening in the Pacific Northwest
- Cold Soil Solutions – Tips For Warming Up Soil In The Spring
- Why Warming Soil for Early Planting Makes Sense
- How to Pre-Warm Soil
- For more information
- Respect the soil in your garden: Don’t add plastic to it
One Harsh Winter!
We had one of the coldest winters on record here in Wisconsin. At one point we even hit -50ºF with the windchill…now that is cold!
In preparation for spring planting, I had to think a bit out of the box this year. You see we still have snow on the ground, which actually isn’t all that unusual for this time of the year in Wisconsin.
Before I can even think about planting seeds (cool weather seeds) out into my garden, I must first thaw the soil out first.
Getting A Jumpstart On The Growing Season
Now I have already started my seeds indoors, but some of my seeds (like lettuce) do best sowed directly into the soil.
If you are interested in growing your seeds indoors here is a great video to help you out!
So when your seedlings are ready or if you are planning on sowing some seeds into your soil, you will need your soil thawed out.
Warm Your Soil Up For Early Planting
So it really is quite simple to warm your soil up. You will need Black Plastic Sheeting and some bricks or stones to hold the plastic down.
Simply drape theBlack Plastic Sheeting over the garden bed you wish to thaw out and put bricks around the perimeter to hold the plastic in place.
Black Plastic Sheeting is important because it will heat up faster and thaw out the soil quickly, so be sure that it is black.
Here is what your bed should look like when finished. Now just wait. Depending on the weather, it could take anywhere from 3-7 days to thaw out.
Once thawed out, your soil will be ready for early planting. I have a post coming out this week to add a simple mini greenhouse to this raised bed so stay tuned for that!
CORVALLIS, Ore. – Spring is here and you’re raring to get your garden in. Well, hold on just a minute. Sowing seed or planting seedlings at the wrong time will bring nothing but heartache.
One of the biggest mistakes people make is to plant too early,” said Weston Miller, a horticulturist with Oregon State University’s Extension Service. “They get excited when it’s sunny for a few days, put plants in the ground and think they will grow. But the seeds either rot from damping off fungus or germinate very slowly. At the very least, they’ll be stressed for the rest of the season and never catch up.”
Right about now in the Willamette Valley, you can get away with planting cool-season vegetables like peas, arugula, mustard, radish and turnip in prepared planting beds. Also, carrots, beets, scallions, chives, parsley and cutting greens that are easy to grow from seed; or plant already-started transplants of kale, head lettuce, chard, leeks and onions.
An inexpensive soil thermometer helps keep planting time in perspective.
“Fifty degrees is a good benchmark for cool-season crops,” Weston said. “And the soil should be 60 degrees or more for warm-weather plants like tomatoes, peppers and basil. In fact, for tomatoes it should ideally be 65 to 70.”
If you can’t resist the urge to plant warm-season vegetables, Miller recommended using some sort of protection from the chill like floating row cover, individual glass or plastic cloches or even milk jugs or soda bottles with the top cut out and turned upside down over plants. For directions on building a large, greenhouse-type cloche with PVC pipe and plastic, check out the OSU Extension guide on How to Build Your Own Raised Bed Cloche.
Whether the relatively warm winter will mean soil warms earlier this year is a matter of conjecture, Miller said. There still could be a cold snap this month.
“Gardening depends on the weather, which is unpredictable,” he said. “But it pays to wait.”
You’ll find more information about vegetable gardening, including schedules for planting 45 vegetables in all regions of Oregon, in the comprehensive Extension publication called Growing Your Own. You’ll also find information on how far apart to space plants and how much to grow for a family of four.
Weston Miller’s top 5 tips for a successful vegetable garden
- Prepare the soil. Before planting, add a moderate amount of compost (¼- to 1-inch) and a balanced fertilizer (all three numbers on the bag are the same) according to package directions. Incorporate the materials into the top 8 to 12 inches with a digging fork or spade. Rake bed before planting seeds or transplants. For new garden beds: Remove sod or weeds to expose soil. Liberally add 4 to 6 inches of compost, agricultural lime and a balanced fertilizer and incorporate into the top 8 to 12 inches with a digging fork or spade. Prepare seed or transplant bed with rake. Next fall, add 5 to 10 pounds per 100 square feet of lime to beds.
- In addition to adding complete fertilizer to the soil, use a soluble fertilizer like fish emulsion for transplants, especially early in the season or if the plants are not thriving.
- Use transplants when possible. Crops that do best when seeded directly into the garden include carrots, parsnips, beets, radish, turnips, mustard and arugula. Most other crops can and should be transplanted to make the gardening process easier, particularly for weed control. Grow your own transplants or look for high-quality starts (not root bound, stunted, off-color) at the garden center for best results.
- Control weeds early in the growth cycle of your veggies. Plan to weed your veggie beds at least once per week for the first four weeks of the plants’ growth to get the edge on this ongoing challenge in the garden.
- Monitor and control slugs and other insect pests, often. Keep an eye out for slugs. Find them under debris and in the folds of plants and dispatch them by dropping into soapy water or cutting them in half with scissors. Look for aphids, imported cabbage butterfly larvae, and other pesky critters on the underside of the leaves. Squash them!
5 Essential Tips for Vegetable Gardening in the Pacific Northwest
As a home gardener for the past 26 years, I’ve learned much when it comes to growing vegetables — and I have been deeply satisfied by the opportunity to grow nutritious food for my family. However, it can be a definite challenge to grow veggies like those found in your local market — especially in our fickle Pacific Northwest climate. Throughout the years, I’ve checked in with professional gardeners, I’ve read “the bible of Northwest gardening,” Growing Vegetables West of the Cascades, and with a little help from Seattle Tilth and fellow urban farmers, I’ve been able to transform my garden. With a little trial and error, you can too!
1. It’s the soil… and how you prepare it
To grow great vegetables, you’ll need to start with the right soil. Most soils are a combination of sand, silt, clay, and organic matter, with the percentage of each component determining what type of soil you have. Given Seattle’s past glacial cover, you are likely to find both sand and clay soil types in your yard.
Sandy soil is easy to till and it drains well, but that is also the problem — it doesn’t retain water or nutrients very well. Loamy soil is what you are hoping for! This soil is easy to work, drains well, and retains moisture and nutrients for overall good soil composition. Clay soil drains poorly and be can be hard to work with — it clods when wet and is dusty when dry. Seeds struggle to emerge from clay soil, and plants have a hard time growing successfully.
A simple test for assessing your soil type is the “squeeze test.” Wait until March or April when the soil has started to dry out from the wet winter. Take a handful of moist (but not overly wet) soil from your garden-bed-to-be and give it a firm squeeze.
- If the soil falls apart, you have sandy soil.
- If the soil holds it shape but falls apart when you poke it, you have loamy soil.
- If the soil holds it shape even when poked, you have clay soil.
So now you know what soil type you have… what, if anything, should you do about it? For sandy soil, till two inches of organic compost into the top few inches of your garden. It is especially important that the top inch or two have adequate compost to help support seed germination.
If you have loamy soil (lucky you!), you’ll only need to worry about tilling it while wet, and possibly mixing one-quarter of an inch of organic compost into the top six inches of soil.
Despite the love and good intentions of even the best gardener, clay soil will not be transformed into good gardening soil — I learned this the hard way. It will not mix properly or embrace added compost. Instead, plan on buying some good-quality vegetable garden soil and place about six to eight inches ON TOP of the existing soil. Dig down through the new soil and into your existing soil about three inches. Till well together, and you’ll be on your way to having great soil! This process helps to create mounds, and is often why urban gardeners opt for raised planter beds to hold their new soil in place.
No matter what type of soil you have you will need to prepare it for planting, so get ready to do some work. If it is a new planting area, dig up the grass or other plants and make sure all of the roots are removed. Take a shovel and turn over the soil (dig it up a couple of times), going at least a foot deep. Your soil should be turned every spring, even in existing garden beds. You may also need to break up clumpy dirt and pull out leftover roots from last season.
Depending on what type of soil you have, augment with organic compost as needed. On my existing beds, I mix in about half an inch or so of organic vegetable bed compost. I turn the top six to eight inches of soil over again and level with a rake or hoe. Now the beds are almost ready for planting!
2. It’s the fertilizer… and you make it!
Besides great soil, plants require fertilizer to flourish and produce. When possible, consider making your own organic fertilizer as it can be hard to find a prepared mix that is suitable for the unique mineral composition of Pacific Northwest soil. Here is a helpful recipe from Steve Solomon that is perfect for our environment. All of the organic components can be found at local nurseries or garden stores.
- 8 dry cups cottonseed meal
- 1 dry cup lime — use dolomite
- 1 dry cup phosphate rock
- 1 dry cup kelp meal
This 11-cup mix will make enough to broadcast over approximately 50 square feet of garden space. Dig or hoe this into the first four inches of tilled soil before you plant your seeds. Garden experts recommend side dressing every four to six weeks, but I have never done this (shame on me — I pledge every year to be better!). I do re-fertilize the soil if I am planting new seeds or a second crop after the first has been harvested.
If you don’t want to make your own fertilizer you can buy a great blend from Walt’s Organic Fertilizer in Ballard.
3. It’s the timing… and the weather
Here’s where things get a little tricky. Different vegetables need to be planted at different times. Follow guidelines flexibly, and pay attention to the weather. Here in Seattle, we can have spring weather where the average temperatures run five or six degrees above or below normal. This differential will definitely affect the chances of your seeds germinating. There have been years when I have had to replant my seeds because it was too cold for them to germinate and they rotted in the soil.
Reference the required soil temperature listed on each seed package and then take the soil temperature. I use an instant thermometer to do this, but soil thermometers are also available at garden supply stores. Between noon and 2 p.m., insert the thermometer two inches into the soil where you plan to plant and record the temperature. Repeat this step for three to four days in a row and average the resulting temperatures. When the soil registers as warm enough, begin planting!
For heat-loving vegetables such as beans, cucumbers, squash, and corn, the soil needs to be above 60 degrees and night temps need to remain above 50 degrees. Plant these veggies when it looks like we will be having a stretch of warm sunny days.
Though planting is ultimately determined by the soil and air temperature, I make a planting schedule after deciding on what will be grown. Following advice is sound for growing vegetables from seeds sowed directly in the garden.
- First planting in mid-March — peas
- Second planting in late March/early April — beets, scallions, cilantro, carrots
- Third planting in mid-April — lettuce, broccoli, spinach, chives, fennel bulbs
- Fourth planting in late April/early May — carrots, cilantro, dill, cauliflower
- Fifth planting in May — pole beans, summer squash, lettuce
- Sixth planting in early June — cucumbers, corn
- Nursery-bought plants — the biggest that I can find
Given that we can have cold springs, many of these dates can get pushed back. One year I had to replant my squash and green beans, and the beets weren’t growing at all so I pulled them in late May and used the space for more tomato plants. The watchwords for gardening in the Northwest: flexibility and patience!
4. It’s the spacing
Try to buy your seeds from a Northwest seed company, as they will have varieties that can grow in our shorter growing season. Follow the seed package spacing and thinning instructions when you plant. This can be frustrating for urban gardeners who want to get as much as they can out of a small planting area. I only started getting vegetables that looked like those you see at the market when I stopped crowding my plants. Yes, lettuce really does need to be spaced 12” apart to get a real head — don’t fight it! Here are spacing recommendations that I use in my garden:
- Beans — pole; thin established plants 8”-10″ apart.
- Beets — plant rows 18” apart; when seedlings are 3″ high, thin to 1″ apart for baby beets, 3-4″ for mature beets, 6″ for winter storage beets.
- Broccoli — center plants 24″ apart in rows 4′ apart. Complete thinning when the plants have three true leaves.
- Carrots — plant rows 18″ apart; when seedlings are 2-3″ tall, thin to 1 1/2″ apart.
- Cauliflower — center plants 24” apart.
- Corn — needs to be grown with at least four rows 30″ apart. Thin plants to 8″ apart in the rows. Corn needs to be grown in a block so it can pollinate itself. If you don’t have an area at least 8’ by 4’ receiving eight hours of sun, consider other vegetable options for that space.
- Cucumbers — space 18″ mounds about 2-3′ apart. Plant four to five seeds; when seedlings have first true leaf, thin to one plant per mound.
- Lettuce — plant rows 24″ apart, thin seedlings for loose-leaf 10-12″ apart; for iceberg, bibb and romaine, thin to 12-14″ apart. When plants are 2-3″ in diameter, sow new rows in between the started ones. This will keep you in lettuce all summer! Remember to add fertilizer when you plant where you have harvested.
- Parsley — plant rows 18″ apart, thin plants to 3″ apart.
- Peas — plant rows 18′ apart — do not thin.
- Radishes — plant rows 12” apart; thin plants to 2” apart.
- Spinach — plant rows 14-18″ apart, thin seedlings to 3″ apart when plants are 3″ in diameter, then thin to 6-8″ apart if you want large plants to pick leaves from.
- Swiss chard — plant rows 18″ apart; thin seedlings to 10-12″ in the rows.
- Squashes — space mounds 2-3′ apart, in rows 4′ apart. Sow three to four seeds; thin to one per mound.
- Tomatoes — center plants two to three feet apart.
- Zucchini — summer; space mounds 2-3′ apart, in rows 4′ apart. Sow three to four seeds; thin to one per mound.
5. It’s what you grow
Here’s the fun part — deciding what you’d like to grow! Plant what you like to eat and what will work in your yard, soil- and space-wise. Not all vegetables do well in Seattle, given our short cool summers. Forget warm-weather crops like eggplant and peppers! Here are 16 veggies that do well in the Pacific Northwest.
- Beans — fun to watch and they keep on delivering! Not too fussy about soil type, but pole beans need something to climb on, up to 7’ high.
- Beets — any soil type works.
- Broccoli — best grown in loamy soil, but will tolerate other soil types. Broccoli can also be planted in the fall for an early spring crop.
- Carrots — germination time is long, so be patient! Carrots do need well-tilled loamy soil to mature beyond the pudgy stub state.
- Cauliflower — said to be a difficult vegetable to grow, but I’ve had great luck!
- Corn — fresh corn is the best. Almost any soil will do, just make sure it is well fertilized. As I mentioned earlier, plant only if you have the space and hope for a warm summer!
- Cucumbers — loamy soil and warm weather are needed, but it’s fun to find the cucumbers growing amongst the vines.
- Lettuces — thrive in well-fertilized loamy soil, but thinning is needed to produce big heads. Replant every few weeks to enjoy fresh lettuces all summer long.
- Parsley — loamy soil is a must. Plants will last through the winter.
- Peas — an early planting and producing crop, peas need loamy soil. Some peas don’t need a trellis, but snow and snap peas may; read the seed package carefully.
- Pumpkins — vines need a lot of space and heat; start indoors and transplant when it is warm.
- Radishes — an early crop that requires loamy soil; fast growing, so a late-planting vegetable can take its place when harvested.
- Spinach — needs loamy, well-fertilized soil; underground pests and bad weather can deter you, but keep trying.
- Swiss chard — a poor-soil-forgiving plant that is beautiful and will grow through the winter.
- Squashes summer — need loamy warm soil and room; will produce for a couple of months; be sure to plant colorful cosmos nearby to attract bees!
- Tomatoes — a ripe tomato off the vine is like eating sun candy! Buy mature plants from a nursery that will grow in our cooler summers. I always plant a couple Early Girls and at least one roma or plum-type tomato plant. Most plants will need to be staked as they grow, with the new growth tied up every couple weeks. Towards the end of the summer, nip new flower growth and don’t overwater when the fruit is ripening.
This article was updated on March 19, 2019.
Cold Soil Solutions – Tips For Warming Up Soil In The Spring
As winter drags on, gardeners are thinking about spring. And the earlier we can get out there growing, the better. You can actually help warm up your soil quicker so that you can start planting sooner. Cold soil solutions are simple and easy to implement.
Why Warming Soil for Early Planting Makes Sense
For your perennials and flowers, there is really no need to get started early with growing, but for your vegetable garden, why not get some of your early plants in the ground even earlier? It is possible to make your soil conditions just right for some of those hardy early vegetables like greens, radishes, peas, and beets.
Warming up soil in late winter or early spring means that you can start these vegetables early and get a harvest sooner. Starting earlier will also allow you to get more harvests out of your growing season or will give you more space to start growing your summer and warmer-weather plants.
Hardy, early plants
can start growing when soil temperature has reached about 44 degrees Fahrenheit (7 degrees Celsius) for a consistent period.
How to Pre-Warm Soil
First, it’s important to have the right kind of soil and moisture levels. Even soil with plenty of organic matter and good drainage will hold onto just enough water to keep the soil warmer than dirt that is bone dry. Having water in the soil—but not enough to saturate it—will allow it to absorb and hold onto daytime heat better.
Of course, that won’t be enough for most climates. To really warm up the soil, you need some artificial methods. Cover the soil with plastic sheeting and leave it in place for about six weeks. This is approximately how much time is required to heat the soil enough for early plantings.
Once you’re ready to sow, take off the cover, pull any weeds, and sow the seeds or transplants. Then recover if it’s still cold outside. Be sure to weight the plastic firmly while warming up soil to ensure it stays in place.
Keeping soil warm over winter is another option for gardeners living in areas where winters are not too harsh. It seems counterintuitive, but don’t use mulch over the soil. This will prevent the soil from absorbing heat from the sun during the day. Instead, till the soil around your plants to loosen it up to a depth of 2 or 3 inches (5 to 8 cm.); this will help it better absorb heat.
Sprinkle dark compost over the surface as well to absorb more heat. If these methods aren’t enough, you can also use the plastic sheeting to hold in heat.
Whether you’re warming up for an early spring or holding heat in over a mild winter, warming the soil is possible, and is a move that will reap great rewards come harvest time.
Soil solarization is an environmentally friendly method of using the sun’s power to control pests such as bacteria, insects, and weeds in the soil.
The process involves covering the ground with a tarp, usually a transparent polyethylene cover, to trap solar energy (Fig. 1). The sun heats the soil to temperatures that kill bacteria, fungi, insects, nematodes, mites, weeds, and weed seeds.
To solarize your soil:
- Clear the area of plants and debris.
- Water the soil deeply until it is wet.
- Cover the area with clear plastic (such as 1 to 4 mil painter’s plastic). Don’t use white or black plastic; they don’t allow enough heat to get to the soil.
- Bury the plastic edges in the soil to trap the heat.
- Leave the plastic in place for at least 4 weeks in the hottest part of the summer.
- Remove the plastic.
Soil solarization works best on heavy soils—those containing clay, loam, or mixtures of them. They can hold more water than can light soils, long enough to produce steam every day. Steam is needed to kill nematodes, weed seeds, and insect eggs in the soil.
Solarization may be less effective on sandy soil, which drains faster and produces less steam. To maximize the benefit of solarization in sandy soils, lay drip irrigation lines under the clear plastic cover and add water regularly.
Normally, water beads will appear on the underside of the plastic early each morning and disappear by noon after the water has turned to steam. The next day, the water beads appear again. When fewer beads appear in the morning, it is time to turn on the irrigation and replenish the water in the soil.
Any area can be solarized as long as the plastic cover is large enough to cover the intended area (Fig. 2). Keep in mind that you need weed-free soil, plenty of water, and plastic with the edges buried for 4 weeks in July to get the most benefit from solarization and still have time to plant your fall garden.
Soil solarization is also used on a commercial scale (Fig. 3). To reduce labor cost of removing the clear plastic and laying down black plastic for production, the clear plastic is sprayed with whitewash after the soil has been solarized. Once the soil temperature drops to normal levels, the growers can plant their crop directly into the beds.
Research by horticulturists of the Texas A&M AgriLife Extension Service has found that soil solarization can suppress weeds both short and long term.
We studied the effects of soil solarization under varying conditions in 2011 and 2012. In each study, we prepared two 10- by 10-foot plots by removing all plant debris and saturating the soil with water to a depth of 6 inches. Then we covered one plot with clear plastic and secured the edges to contain the heat and steam produced.
The study compared the air and soil temperatures of bare-ground and solarized soil for about 30 days in 2011 and 2012 (Figs. 4 and 5). In both years, the solarized soil reached much higher temperatures— up to 180°F—than did the control plot,which reached only 115°F and 120°F.
In 2011, the lowest soil temperature recorded in the solarized plot almost equaled the highest temperature in the bare-ground plot, about 120°F. In 2012, the minimum soil temperature in the solarized plot was 98°F, compared to the maximum temperature of 108°F in the bare-ground plot.
Four weeks after removing the tarp, we found 90 germinated weeds in soil taken from non-solarized plots and three from soil taken from solarized plots in 2011. In 2012, we found 300 germinated weeds from non-solarized soil and 19 from solarized soil.
In another study, we measured the temperature of solarized and non-solarized soil for 73 days beginning September 23, 2012. We rototilled two 10- by 10-foot plots and removed all plant debris from them. An overhead sprinkler applied water to the plots for 24 hours.
One day later, we covered one of the beds with clear plastic and secured the edges of the plastic with soil. The control bed consisted of bare ground.
We recorded air and soil temperatures daily at a 6-inch depth in both beds (Fig. 6). We removed the plastic on December 4.
As in the previous study, the minimum soil temperature of solarized soil in 2012 was about the same as the maximum temperature of soil in the control plot of bare ground. Immediately after the tarps were removed, the solarized plot had no weeds.
Figure 7 shows the weed pressure 3 weeks after the plastic cover was removed. The solarized bed had few weeds, and those present consisted of newly emerged grasses, mostly near the edges of the plot. The bare-ground plot had significant pressure from both annual and perennial weeds.
On March 12, 2013, or 147 days after the plastic cover was removed, the solarized plot had only perennial weeds (Fig. 8A). The control plot (Fig. 8B) had broadleaves as well as annual and perennial grasses.
Home gardeners and crop producers can use solarization to significantly reduce weeds long and short term.
However, because solarization kills all organisms—even the beneficial ones—farmers and gardeners should replace the beneficial organisms by adding compost to the soil after it has been solarized.
For more information
“Solarization and biofumigation help disinfest soil.” By J. Stapleton, C. Elmore, and J. DeVay. 2000. California Agriculture 54(6):42–45. University of California.
Soil Solarization for Gardens & Landscapes: Integrated Pest Management for Home Gardeners and Landscape Professionals. University of California Agriculture and Natural Resources. http://ucanr.edu/sites/Solarization/files/114635.pdf
Download a printer-friendly version of this publication: Soil Solarization
View more Gardening & Landscaping information “
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Respect the soil in your garden: Don’t add plastic to it
Before it’s too late, I must address one of my pet peeves: deliberately putting plastic in soil.
Take, for instance, black plastic sheeting sold as mulch. This stuff appears at first to be a cure-all for weed problems. Lay it on the ground, cut holes only where you will set plants, and weeds will die from lack of light, presumably ending all your weed problems for years to come.
But other problems arise. An impermeable sheet of plastic over the ground can leave plant roots and soil microorganisms gasping for air. Roots set in the openings might develop even greater breathing problems when all the water falling on the plastic floods those holes.
And the plastic eventually starts to tear and break apart, which creates a general mess.
Geotextiles, introduced more recently, are offered as an alternative to solid black plastic sheeting. These are woven or spun plastic fabrics that resist tearing and have many small holes to allow passage of air and water.
Both black plastic and geotextiles are widely used by farmers, gardeners and landscapers. If you don’t like the way these synthetic mulches look — surely the case when they are used in landscaping — you cover them. Wood chips look natural and are widely used for this purpose. And anyway, geotextiles need a thin cover of something to shade out the minimal light that makes its way through the tiny holes.
But problems arise again. Over time, plenty of weeds eventually sneak in to grow in the wood chips covering the plastic. Over time, the chips or other coverings also slide around to expose the plastic or geotextile beneath — not a pretty sight!
Furthermore, even if black plastic or geotextiles don’t do their jobs forever, they’ll be in the soil that long, or almost. Try to make over the landscape in the future and you will be wrestling with and cutting geotextiles or collecting scraps of black plastic.
PLASTIC PEANUTS, NO
Another, fortunately less frequently suggested use of plastic in the soil is plastic “peanuts.”
Mixed into the soil, the reasoning goes, they should increase aeration. While they would undoubtedly make a soil lighter, and thus seemingly better aerated, all that extra air is pretty much locked up in the peanuts.
It has also been suggested that a layer of plastic peanuts be put in the bottoms of flowerpots to enhance drainage, as layers of gravel have been used. In this case, that layer of peanuts is worse than useless, just as the traditional layer of gravel was. The effect in both cases is to create a “perched” water table inside the pot, giving the roots less depth of well-aerated soil.
Also, spent potting soil can be spread on the ground or added to a compost pile, but do you want the peanuts there also?
ENVIRONMENTALLY FRIENDLY ALTERNATIVES
Enough plastic makes its way into our soils inadvertently, from misplaced plant tags to those stickers now ubiquitous on fruit skins to pieces of old plastic pots.
Deliberately embedding a permanent, synthetic blanket in the ground or mixing plastic peanuts into the soil brings no benefits that could not be had in a more nature-friendly way. Paper mulch, for instance, biodegrades and can stave off weeds for a season. Perlite or vermiculite are two minerals that can lighten a soil more effectively than styrofoam peanuts.
Removing plastic put on or in the soil becomes difficult or well-nigh impossible.
Deliberately putting plastic in the ground is disrespectful of the skin — that is, soil — that covers our planet and sustains much of the life here.
Garden soil, covered in plastic for a few days before planting, helps warm it up. The plastic should be sealed tightly against the soil. Then cut slits in the plastic where you plant. (Bob Morris)
Q: I have some tomatoes and pepper plants in pots. They are about 18 inches tall. Is it too early to plant them in my raised bed garden? It’s been too cold lately to plant.
A: You’re right, it’s been unusually cold. Both the air temperature and soil temperature are excessively cold for good plant growth of warm-season plants such as tomatoes and peppers. These are tropical plants, what we call “warm season,” and grow best at temperatures from 60 to about 95 degrees. They need enough new leaf, stem and root growth to get established and stay ahead of damage from disease or insects.
How do you know if the soil temperature is warm enough? It is important that day temperatures are warm but nighttime soil temperatures can be cooler, down to about 45 F. A soil thermometer stuck several places in the soil, 1 to 2 inches deep for transplants, will give you a good idea of its temperature. I use an inexpensive AcuRite soil thermometer to do this.
Garden soil, covered in plastic for a few days before planting, helps warm it up. The plastic should be sealed tightly against the soil. Then cut slits in the plastic where you plant. Covering the soil in plastic raises the soil temperature quickly. Covering the soil for two to three days is usually enough.
I prefer tomato and pepper transplants to be about 6 to 8 inches tall when I put them in the ground. At this size, they can handle a little bit of abuse, and they are not so large they suffer from noticeable transplant shock after planting.
Expect large plants like yours to go into a few days of shock before they start growing again. Warmer temperatures help them to recover faster.
If plants are really big, I pinch the tops back so the top and roots are in balance. It’s inevitable to have some root damage from planting. Pinching the top back helps to compensate for this root damage.
Transplant shock is an adjustment period the plant goes through when removed from a container and planted into a garden soil — from a protected environment in the nursery or greenhouse to a more hostile garden environment. All plants go through transplant shock. Smaller plants adapt quicker to a new environment than larger plants.
Q: I was reading about pheromone traps for insect control on fruit trees. Can I use pheromone traps to reduce the need for chemical spraying and which insects are attracted to them?
A: Pheromone traps release insect pheromones, or “scents,” that attract other insects needed for their reproduction or survival. Pheromone traps are used to either determine when spraying insecticides is most effective or, in some cases, to reduce the need for spraying insecticides altogether. A different pheromone trap is required for each insect.
Pheromones are not available for every insect but a different pheromone is required for each insect you want to control. Two insects I have successfully caught in pheromone traps include the peach twig borer (wormy peaches) and coddling moth (wormy apples and pears). I have been successful using them in what is called “mating disruption” and totally avoided the need for spraying chemicals to control these two pests.
The trap is made from cardboard with a sticky bottom surface combined with a rubber lure impregnated with a chemical pheromone. Buy the winged traps and not the Delta traps and the highest concentration of pheromone you can buy in a lure. The trap combined with a fresh lure is hung in the branches of trees you want to protect.
Hang traps with the lures in the trees beginning in about April. Replace the old lure with a fresh one about every 30 days. The sticky surface of the trap should be replaced when it gets dirty or full of insects. I will offer a class on pheromone traps in early April. Watch for it on Eventbrite.
Q: What type of grapes should I grow to make raisins? Is there any special trick to making raisins or do you just dry the grapes?
A: Traditionally, Thompson seedless is used for raisins, but you can use any seedless raisins (usually table grapes). Whichever taste of grapes you like make good raisins. Allow them to dry on the vine (unless birds or ground squirrels are a problem) or remove them from the vine and dry them by themselves.
Remove the berries from the bunches and remove the stem from the berry. If there is a secret to drying fruit in the desert, it is to control the temperature used for drying.
I made a solar dryer a few years ago, but the air temperature in the dryer was too hot. I ended up using this dryer but put it in the shade rather than in the sun.
Cover the drying grapes with cheesecloth or any breathable material that helps keep birds and dirt off of it. Temperatures should be below 140 degrees, but suggestions will vary. Generally, the lower the temperature and high wind movement the better. Think low temps and a fan.
So drying them in the shade in open air in the summer is about perfect here. Just avoid high temps (above 140 degrees) and dry them as quickly as possible.
Q: Is it too late in the year to replace a flowering plum tree? Another tree in my yard is starting to blossom.
A: Whether to plant a new flowering plum tree or not has nothing to do with its flowering time. The best time to plant is just before new growth begins in the spring which is a week or two before flowering. But there is nothing wrong with planting any time during the spring. It just so happens planting time also corresponds to flowering time as well.
Another great time to plant is during the fall months when temperatures are beginning to cool, when it is not yet cold, and before leaf drop. In the Mojave Desert, the spring begins around the first week of February, give or take, and the fall begins toward the latter part of September.
I’m curious about why you are replacing a flowering plum tree. If this was because of borers that tunnel into the limbs and trunk, then you are fine planting in the same hole. These insects do not get into the soil but spend their entire life above ground.
However, if you are replacing this tree because of overwatering problems then it’s best not to plant in or near the same hole. Root diseases like collar rot stay in the soil and could pose a future problem for most trees and shrubs planted there. Plant several feet from this area.
Q: What type of fertilizer do you suggest for table grapes? Mine have been in ground three years now, and the production has been less than I hoped. I have been using compost and worm castings twice a year.
A: The problem may not be the fertilizer or how much you are applying but how the vine is pruned. There are two general methods of pruning grapes. Some grapevines are pruned using the spur method while others are pruned using the cane method.
Grapes that should be pruned using the cane method may produce little or no fruit if they are pruned using the spur method. However, grapes that require spur pruning will produce fruit if they are cane pruned.
The difference between the two is the amount of last year’s growth left attached to the vine. In spur pruning, last year’s growth is cut back severely, leaving less than an inch remaining. In cane pruning, last year’s growth is cut back so that about 8 to 10 inches of growth still remain attached to the vine.
Bottom line, if you are not sure how to prune your grapes, leave last year’s growth 8 to 10 inches long. Last year’s growth will be a different color than the older parts of the vine. Sometimes it’s reddish-brown and sometimes it’s yellowish-brown. When the fruit emerges, re-cut the cane to a better length.
Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to [email protected]