Is your land good for walnut trees?

Most land is good for walnut trees.

Walnut trees grow and produce well in a very wide range of places. They are grown as a business in France, Italy, Spain, Turkey, the Balkans, Central Asia, Chile and California. These places have very different soils, rainfall and winters. If your neighbours grow fruit or nuts, walnuts will very probably work on your land too. A few simple checks before you plant show you which part of your field to use, which variety to choose and what to prepare.

How to check your land, step by step

You do not need to do all of this in one week. Do the steps in this order, because each step tells you whether the next one is worth doing.

1. Look at the climate. Check whether there is late frost in spring and whether the summer is warm enough.
2. Walk around the land. Find where it is high and where it is low. Note where water stays after rain and where fog collects.
3. Ask what grew here before. Old orchards, old woodland and old vineyards can leave problems in the soil.
4. Dig some holes. You need to see the soil down to about 1.5 metres.
5. Send soil and water to a laboratory. One test, before planting, tells you what to prepare.
6. Check your summer water. The supply that matters is the one you will have in the hottest, driest weeks, when the trees are fully grown.
7. Decide, and write down what you decided and why.

Part 1: Climate

Chapter 3, Choosing the Right Variety, explains how to choose. You can also ask us for a recommendation. Tell us where your land is, and we will help.

Late frost in spring

Frost does the most harm after the tree has opened its flowers. A cold night in winter, when the tree is resting, matters much less. The same cold night in April can destroy the crop if the flowers are open.

A later variety lowers the risk from frost, but it does not remove the risk. It also does not turn a cold hollow into good ground. Choose the right place and the right variety together.

Is your summer warm enough?

Walnut trees need a warm summer to fill the kernel properly. Cool summers can produce thin shells and light kernels.

Very hot summers are also fine, as long as the trees have water. Above about 38°C, the sun can darken the kernels of nuts on the outside of the tree. This damage happens almost only when the tree does not have enough water at the same time. A tree with enough water cools itself.

So in a hot area, make sure your irrigation is good (Part 3).

Height, slope and wind

• Height above sea level tells you very little on its own. A high slope can be warmer at night than a low valley. Do not use a height figure that was published for another country.
• Where on the slope you plant matters more. Gentle slopes work very well, because the cold air keeps moving.
• A south-facing slope is warmer, and spring starts earlier there. This is an advantage in a cool area and a small risk in a frosty one.
• Wind is mostly fine. Light wind dries the leaves and is good for the trees. Strong, constant wind makes the trees use more water and makes sprinklers work badly. This is one more reason why we recommend drip irrigation. A windbreak is a barrier that reduces the wind, such as a row of trees. If you plan a windbreak, first check that it will not block the cold air from draining away at night.

Part 2: The soil

What grew here before

Old orchards, vineyards and woodland can leave problems in the soil. Some root diseases can stay alive in old roots for years. Ask what grew on the land before, why any trees were removed, and whether they had health problems.

If there was an old orchard, vineyard or woodland, talk to us or a local agricultural adviser before you plant. Do the same if the trees had health problems. The usual preparation is to take out as much of the old root as you can.

How deep is your soil?

What you are looking for

• See how far down the roots can go. Something may stop them: rock, a hard layer, heavy clay or wet soil.
• Old roots. If roots from a previous crop all stop at the same depth across the hole, something is stopping them there. Find out what it is.
• Colour changes. Grey, blue or green soil means the soil is wet all the time. Orange or red spots mean the soil gets wet and dries again.

Most soils in walnut-growing regions pass this check easily. Deep loam soils (a mix of sand, silt and clay) are the best. Heavy clay and pure sand both work but need more care with water.

Does the water drain away?

Drainage is the one soil question worth checking properly, because it is the hardest thing to change later.

Walnut roots need air as well as water. When water stays around them, they cannot breathe. In warm weather, roots start to die after one to three days in soil that is full of water. Wet soil in winter does far less harm, because the soil is cold and the roots are resting.

A field is better used for something else only if it is wet almost everywhere, all year, with nowhere for the water to go. Such fields are rare.

Good practice whatever your soil: water should soak in within a day or two, and water should never stand against the trunk. If your soil takes water slowly, give smaller amounts more often. Watering for longer does not push the water deeper. The water only stands on the surface of the soil.

Soil pH and lime

Walnuts accept a wide range of pH and produce well from about pH 5.5 to 7.5. The best range for absorbing nutrients is 6.5 to 7.2.

• Below 5.5, ask the laboratory for a lime recommendation and spread lime before planting. This is easy to do.
• Above 7.5, especially on chalky or limestone soils, the tree finds it harder to absorb iron and zinc. This is very common around the Mediterranean, and growers manage it routinely with carefully placed fertilizer and sprays on the leaves.

You cannot change the pH of a deep chalky soil. No amount of sulphur will change it at a reasonable cost. So on chalky ground, work with the soil as it is. Ask for a calcium carbonate test so that you know how much lime the soil contains. Then use the result to plan your feeding with trace elements (nutrients that the tree needs in very small amounts).

Salt in the soil and water

• Soil and irrigation water can contain salts that affect walnut trees. Salt matters mainly in dry regions, near the coast and on land that has been irrigated for many years with hard water. In most of Europe and inland Turkey, a test finds no problem.
• Include salt testing when you arrange your soil and water analysis. Walnuts are more sensitive to salt than many crops, so one laboratory test is worth having. The next section lists the tests to ask for.
• Ask the laboratory or an adviser what the results mean for you. Ask whether the soil needs any preparation, and whether your water supply needs any change. You do not need to read the numbers yourself.

Arrange your soil and water tests

• Contact an agricultural laboratory first. Explain that the field is for walnut trees, and ask for its sampling instructions and the tests it recommends.
• Divide the field into areas that look different. Look for a different colour, a different slope, wet corners, old stream beds or an old farmyard. Test each area separately. Do not mix the areas into one sample, because an average hides the problem.
• Take samples below the surface, not only at the top. A good topsoil sample tells you nothing about what is at one metre.
• Send your irrigation water at the same time, to the same laboratory, and ask for both reports to be read together. You can only understand soil salt and water salt when you read them together.

Part 3: Water

Before planting, check whether your land will have enough water during the hottest, driest part of summer. Walnut trees need a reliable supply to grow well and produce good crops.

Will I need irrigation?

If your summers are usually dry, plan to install irrigation before planting. Irrigation means supplying water to the trees through a watering system.

In wetter regions, some orchards can produce well using rainfall and water stored in deep soil. Ask nearby walnut growers whether their trees still produce good crops in dry summers, and whether they need extra water. Their experience is most useful when their soil and growing conditions are similar to yours.

Young saplings need particular attention because their roots reach only a small area of soil. They may need watering even where established trees grow without irrigation.

If your water supply is limited, choose an orchard size that you can water reliably.

Check your water supply before you order trees

A well, stream or canal may provide plenty of water in spring and much less in late summer. Check how much water will be available when the trees need it most.

Give the supplier your field size, soil information and water-test results. Include the planned tree spacing (the distances between trees and rows). Ask for a watering plan showing which sections to water, how many hours to run the system, and how to adjust watering through the season.

Ask the supplier to state the orchard area that your water supply can reliably support. If your water is limited, this tells you how much land to plant.

Test your irrigation water

Water that looks clear can still contain salts or other substances that affect walnut trees.

1. Before planting, send a water sample to an agricultural laboratory, following its instructions for collecting the sample.
2. Explain that the water is for walnut irrigation and ask for an assessment together with your soil results.
3. Ask the laboratory to explain whether the water is suitable or needs special management, and whether another supply is necessary.

Choose an irrigation system

Drip irrigation is a good option for many new walnut orchards. It delivers water slowly near the roots and allows you to water different parts of the field separately. Microsprinklers (small sprinklers) can also be useful where a wider area of soil needs watering.

When installing and using the system

• Place the outlets, where water leaves the pipes, close enough to wet the soil around the young roots. Avoid keeping the soil against the trunk constantly wet.
• As the trees grow, increase the area of soil you water. This may mean adding outlets, a second drip line (a pipe with drip outlets) or changing the layout. Ask the installer to plan for these changes from the beginning.
• Keep the system working. Choose a filter that suits your water, and check the whole field while the system runs. Chapter 6, Irrigation, explains the routine care.

How do I know when the trees need water?

Check the soil around the roots regularly. The surface can look dry while the soil below is still moist. Light rain can also wet the surface without reaching the roots.

For young saplings, choose a small area beside the roots, within the watered area. Check the soil about 20 to 30 cm below the surface, taking care not to damage the roots. As the trees become established, check deeper too. Use a hand auger to make deeper checks easier. This tool takes soil from below the surface.

Check several places, including sandy areas and trees at the far end of the irrigation pipes. Newly planted trees need daily checks during very hot weather.

How often should I water?

The right schedule depends on your soil, the weather, tree size and irrigation system.

Sandy soil usually needs smaller amounts of water more often. Heavier soil generally holds water longer and may need more time between waterings.

Trees usually need more water in hot, dry or windy weather. After substantial rain, check the soil before restarting the normal watering schedule. As the weather cools, reduce watering according to soil moisture and local advice.

Part 4: Using your results

A simple check before you plant

Most fields will be in the “Fine as it is” column or the “Fine, with some preparation” column of this table.

You can contact us before you have collected any of the items below. Use the list to prepare for planting.

Summary

Walnut trees are more adaptable than most people expect. Growers produce good crops on sandy soil, on clay, on chalk, at sea level and at 1,200 metres.

Everything else (hard layers, pH, nutrients and moderate salt) is either fine already or can be fixed before you plant. It is much cheaper to fix now than later.