Growing oak trees from acorns

How to germinate acorns

It is fairly easy to grow an oak tree from an acorn.

Start by gathering mature acorns, when they drop to the ground in the fall. Since they quickly lose their viability if they are stored under dry conditions, it is best to plant them immediately or to stratify them.

Stratification involves placing the acorns in damp sand in a plastic bag and leaving it in the refrigerator – not the freezer! – at (5°C) over the winter. Then you can plant them the following spring. If you don’t have enough room in the refrigerator, another stratification method is to plant the acorns in the fall in pots that you then bury in your garden. Make sure to cover them with a screen or the squirrels may have a feast.

In the spring, you can transplant the seeds that have germinated.

Acorns can be attacked by worms. Destroy them before planting by soaking the acorns in hot water (49°C) for 30 minutes.

Whatever seeds you are trying to grow, it’s important to reproduce the same conditions that encourage them to germinate in the wild.

And whatever method you choose, be sure to use several acorns, as not all of them will be successful.

Yard and Garden: Handling, Germinating and Planting Acorns

AMES, Iowa – Fall is here, and so are acorns, falling from oak trees into yards everywhere. Viable acorns can be grown into oak trees, if properly handled. How is this done?

Here are some tips from Iowa State University Extension and Outreach horticulturists on how to best handle, germinate and plant acorns. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or [email protected]

My oak tree produced just a few acorns this year. Why?

It’s common for the acorn crop on oak trees to vary from year to year. Most oak species produce a good crop of acorns once every two or three years. However, the white oak (Quercus alba) tends to produce a good acorn crop once every four to six years.

Weather and other factors can affect flowering and fruiting. For example, freezing temperatures in spring (when trees are flowering) can damage or destroy the flowers, drastically reducing the fruit crop.

The acorns of white oak, swamp white oak (Quercus bicolor), and bur oak (Quercus macrocarpa) mature in one year. Red oak (Quercus rubra) and pin oak (Quercus palustris) acorns mature in two years.

How do I germinate acorns?

Acorns should be collected as soon as they fall to the ground. Sound, viable acorns can be separated from damaged or unfilled acorns by placing them in water. Sound acorns sink. Most floating acorns are not viable and can be discarded.

The acorns of white oak and swamp white oak should be planted in fall. They will germinate immediately after sowing.

Acorns of bur oak , pin oak, and red oak will not germinate until they have been exposed to cool temperatures and moist conditions for several weeks. Winter weather in Iowa normally provides the necessary conditions to break dormancy. The cold-moist requirement can also be accomplished through a process called stratification. Acorns can be stratified by placing the seeds in a moist mixture of sand and peat moss and then storing them in a cool location.

Suitable containers include coffee cans, plastic buckets and food storage bags. The refrigerator is a good storage location. (Stratification temperatures should be 32 to 41 degrees Fahrenheit.) Acorns of the bur oak require a 30 to 60 day stratification period, while red and pin oak acorns require 30 to 45 days. Acorns of bur, pin and red oaks can be planted in fall or stratified seed can be sown in spring.

When planting acorns, place the seeds one-half to one inch deep. Choose a planting site where the oak seedlings can receive good care for one to two years before they are transplanted to their permanent locations.

To prevent squirrels and other animals from digging up and eating fall planted acorns, cover the area with chicken wire or hardware cloth fencing after planting. Promptly remove the fencing material in spring when the acorns begin to germinate.

There are small, round holes in many of the acorns on the ground. What made the holes?

The small, round holes on the sides of the acorns were likely caused by the larvae of the acorn weevil.

The adult acorn weevil is a brown beetle about three-eight inch in length and has a long, thin snout. Adult females lay their eggs inside developing acorns on trees in mid-summer. The eggs hatch into creamy white, grub-like larvae that feed inside the acorns until fall. In fall when the acorns have fallen to the ground, the fully grown grub chews a round one-eighth inch hole in the side of the acorn, exits the acorn and tunnels into the soil to complete its development.

Squirrels and other wildlife eat or stash away the good acorns, leaving the “holey” (destroyed) acorns on the ground.

How you can help, right now

Oak trees are beautiful, drought tolerant native trees with many benefits for wildlife and people. Valley oaks dominate the floor of the Central Valley and give way to blue oaks and interior live oaks in the foothills of the Sierra Nevada and the interior Coast Range. Oak trees can be planted from acorns with great success if proper steps are taken. There are four steps to planting an oak tree from seed; collecting the acorns, processing the acorns, planting the acorns and irrigating the acorns.

Collection

It is best to collect native acorns in early- to mid-fall before they have fallen to the ground. Scope out some good trees for collecting during the late summer so you are ready when they are. They are ready when they can be removed from their caps without tearing them. Valley oaks are usually ready to collect first, followed by live oaks. Blue oaks are ready later in the season.

Processing

Once the acorns are collected, float test them. Any that float or are soft are bad. A diluted solution of bleach and water can be used to clean them so no mold grows on them during storage. Store them in a refrigerator in a sealed container with something to hold some moisture such as a potting additive (vermiculite works best). The vermiculite should be moist, but not too wet.

Planting

For the best success, acorns should be planted in December or January, after the rainy season has started.

One of the major causes of oak seedling death is predation by small rodents, therefore protecting your seedlings is important. Plant acorns in a milk container with the top and bottom cut off or in a commercially available tree protector. This will also allow you to keep track of where they acorns are planted and protect them from rodents. To ensure success, plant two acorns in each container, so if one does not grow the other will. Push them into the soil on their sides and bury them under half an inch of soil so they do not dry out. A stake can be used to mark the planting site and to keep the tree protector in place.

Planted acorns spend their first few months sending down a long tap root, so don’t expect to see any above-ground growth until March or later.

Irrigation

Summer irrigation will improve the likelihood of your oak tree’s survival and help it grow faster. In order to foster a deep, robust root system deep irrigation is important. A long, deep irrigation of ten gallons of water through a drip irrigation system every week to two weeks is ideal. Irrigate for at least 2 years, lessening the frequency of irrigation as the plants get older.

How to grow your own oak tree

Collect acorns

Gather some acorns from the ground. Choose fat, ripe acorns – nice and brown all over. Ignore any that are green (these are unripe) or dark (these have started to rot).

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Add acorns to compost

Fill a small flowerpot, yogurt pot or plastic cup with peat-free compost mixed with some sand or sawdust. Push the acorns into damp compost mix, one per container. Make sure the more pointed end is facing upwards. Cover with 2–3cm of compost.

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Germinate

Place the containers in a cool place out of direct sun, such as a garage, shed or unheated spare room. If it’s too warm, they won’t germinate.

In spring, check if your acorns have started to sprout. Gently water the tiny seedlings once or twice a week to prevent the compost becoming dry.

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Re-pot your seedlings

When your seedlings are 25cm high transfer them to a larger pot. After one or two years the young trees will be ready to plant in the ground.

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Top tip

Other native British trees that are easy to grow from seed include hazel, alder and beech. Plant them in autumn as above.

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