Walnut, Persian

Juglans regia

Introduction

The Walnut is a big impressive forest tree, that not only produces highly nutritious and tasty nuts, but also very valuable wood (this is prized for cabinetmaking and gun stocks).

Nutrients: The nuts are delicious as well as high in protein, fat (especially omega 3 fatty acids) and minerals (notably calcium).

About Walnut

Hours of winter chill: 500-1000

Size – up to 60 feet x 50ft wide

Zone: 5-9

Blooming period: Mid summer

Fruiting period: September – October

Life expectancy: 100 years

Bearing age: 2-3 years grafted

              6 years seedling (15 years to get a good crop.)    

Yield: 100lb

Days to harvest:

Spacing: Standard tree 40-60ft apart

Ease of growing: Walnuts are pretty easy to grow if you give them the right conditions. Those in my garden essentially grow themselves without any input from me.

Climate: Walnuts need full sun for best nut production, though they don’t like very hot climates. Many varieties need a considerable amount of winter chill, though there are low chill varieties that will grow in mild winter areas. Early flowering varieties are potentially vulnerable to late frosts however.

Soil

pH 5.5 – 7.0

Walnuts do best in a deep, fertile, slightly acid soil that is well drained.

Site: If your soil isn’t very well drained you might consider planting on a hillside, or on a mound.

Planting:

In mild climates walnuts can be planted at any time from late fall to early spring. In colder climates they are usually planted in spring. As with most other plants a small tree transplants better than a large tree and will do better in the long run.

When you get your plants home it is a good idea to get them in the ground as soon as possible, but if this isn’t possible you should heel them in, which means placing them in a trench (this trench has one vertical side and one at 45 degrees, the trees being laid in at 45 degrees and soil is firmed over them to fill the trench). If you buy plants mail order you should unwrap them immediately and soak the roots in water overnight before planting or heeling in.

How: Dig the planting hole 2‑3 times as wide as the root ball, to give the roots plenty of loose soil to grow into. You want the hole to be the same depth as the root ball (or roots if bare root), so it can be set into the ground at the same depth it was growing in the nursery. This is most easily measured by laying a stick across the hole to get the right height. The graft union should be 3-6” above the soil.

Start planting by throwing a couple of shovels of soil (possibly mixed with some organic matter if the soil is poor – to help it hold moisture) into the bottom of the hole. Make this into a slight mound and then spread the roots out evenly over it. You then put some soil in the hole to anchor the tree in place and firm it down. Then re-fill the hole with the rest of the soil (make sure the tree remains vertical). You may also want to add some rock phosphate to the soil as you go.

When you have finished planting the tree should be on a slight mound, so as the soil settles it becomes flat. If it starts out flat it may end up as a slight depression where water can collect (which can be a problem on poorly drained soils).

You then water the tree thoroughly, not only to supply water to the plant, but also to settle the soil and establish contact between roots and soil.

The final step is to spread out a mulch to conserve water, and keep down weed competition (keep this six inches away from the trunk).

It is also a very good idea to put a permanent label on the tree saying the variety and rootstock (and write it down in your garden journal).

Support: Newly planted trees were once routinely supplied with a stake to support them, but it is now thought that trees become stronger more rapidly if not staked. Staking is only usually necessary on very windy sites (especially for dwarf trees which grow on weak rootstocks).

Protection: If gophers live in your area you will have to plant your trees in gopher wire baskets (I make my own to whatever size I need). If other rodents are a problem (they may chew on the bark, stunting or even killing the tree) you may have to use various kinds of metal or plastic mouse guards. These should go several inches into the ground and should have gravel around them to deter digging.

Maintenance: In my experience established trees don’t usually need much attention.

Fertilizing: Heavily bearing trees should be given additional nitrogen in spring.

Watering; Walnuts need consistent moisture for best growth and production.

Pruning: The trees can be allowed to assume their natural shape, or they may be trained to a central leader. They are terminal bearing, which means they produce fruit at the end of new growth and so they don’t really require pruning.

Propagation: Walnuts are easily grown from seed, but the resulting trees take longer to bear and may be more variable. Improved cultivars are often grafted onto seedlings of native Black Walnut.

Pollination: Walnuts are self fertile and monoecious, which means they produce separate male and female flowers on the same tree. However the flowers may not open at exactly the same time, so bigger yields are obtained when there is more than one tree. They are wind pollinated, so pollinating insects aren’t required.

Mulch: A mulch of compost is useful to keep the ground moist and add nutrients. Keep it away from the trunk though, otherwise there is a danger of crown rot.

Pests:

Squirrels: These are a big problem in my garden, taking the nuts as soon as they are ripe.

Codling moth

Walnut blight

Birds

Aphids Be aware that they commonly harbor aphids that secrete honeydew.

Walnut husk maggot

Problems: Walnuts are notorious among gardeners for secreting allelopathic substances that inhibit the growth of some neighboring plants (most affected are alfalfa, blueberry, apple, tomato family, bean family and others). They may also be home to aphids that secrete honeydew onto anything beneath them. Bigger list

Harvest: As the nut ripens the green husk splits and falls to the ground with the nut inside. The nuts must be picked up fairly promptly before squirrels do. Remove the husks under foot as you gather the nuts, then rinse (to remove tannin) and dry in the sun.

Storage: The nuts are dried in the shell for long term storage. A dry kernel snaps easily and will keep for months. Don’t shell them before you want to eat them, as they deteriorate once shelled.

Landscape uses: Walnuts make great big stately shade trees, though of course they take a long time to become big enough to be useful for this.

Unusual growing ideas: Can

Other uses: Walnut trees are prized for both their edible nuts and their beautiful wood. It used to be said that farmers should plant walnuts as an investment for their grandchildren’s college fund. Unfortunately this isn’t for their nuts, but for their valuable wood. Grow a nice straight Walnut and it could be very valuable one day (though you probably won’t live to see it).

Varieties

There are quite a few improved cultivars that are later flowering, more precocious (they bear at a younger age), more disease resistant, or have thinner shells (they aren’t necessarily easy to find though).

Related species:

Persian Walnut can only be grown easily in certain favored areas, fortunately there are other options if you live elsewhere.

Black Walnut (J. nigra) – The nuts are harder to shell and smaller than the Walnut, but have very good flavor. The trees are also more allelopathic.

Butternut (J. cinerea) This species is hardier than Walnut, but the nuts are usually somewhat inferior.

Heartnut (J. ailanthifolia)

This Asian species is smaller than most other Walnuts and shorter lived. The nuts are similar though.

Food uses