Which walnut variety should you plant?
Why the answer is usually Chandler, and the three things about your own land that decide whether Chandler is the right choice.
For most commercial growers, the answer is Chandler.
The evidence supports that answer, and the walnut industry has moved to Chandler. Chandler carries nuts along its side shoots, so it starts to earn money early. Its kernels (the edible part inside the shell) are the lightest in colour of any major variety. They come out of the shell in whole halves. It sells both in-shell (as whole nuts, with the shell on) and as kernel, and it suits a modern, mechanised orchard.
The decision is simpler than it looks. You have to answer three questions.
The three questions
- Does my climate suit a late-leafing, late-harvesting variety (one that opens its leaves late in spring and is harvested late)?
- How many pollenizer trees (trees of a second variety that supply pollen) do I need, and where do they go?
- Can I harvest and dry the crop fast enough to keep the quality that made me choose this variety?
What you are choosing
The choice is a package of three things that have to fit together.
The package
What a variety table can tell you, and what it cannot
Nursery sheets and university tables list many numbers for each variety. Some numbers are properties of the variety, so they stay the same on your farm. Other numbers depend far more on your soil and your management, so they change from farm to farm. Plant breeders have measured this difference.
| What the table says | Can you trust it on your land? |
|---|---|
| Leafing order which variety opens its leaves first, second and third | Yes. Almost entirely genetic. The dates will differ in your country, but the order will not. |
| Bloom timing when the flowers open, compared with other varieties | Yes. You can plan pollenizers from it, then check locally. |
| Shell thickness | Yes. A thin-shelled variety stays thin-shelled. |
| Nut and kernel weight | Mostly. Crop load (how many nuts the tree carries) and water stress still change it. |
| Harvest order | Mostly. The order stays the same, but the calendar date does not. |
| Lateral bearing percentage the share of the lateral buds (the buds on the side shoots) that can bear nuts, for example “90%” | Weak. Less than half of this is genetic. It describes trees grown in one place under one management. |
| Shell seal how tightly the shell closes | Weak. It varies a lot with site, season and crop load. Check it on nuts grown near you. |
Never compare varieties by calendar date from another country. Compare them by the gap between them. Imagine that Chandler opens its leaves about two and a half weeks after the earliest varieties in California. It will do something similar in Turkey or Chile, even though the calendar date will be different. Use a variety that is already growing near you as your reference for the order.
Chandler: strengths and weaknesses
What it gives you
- Late leafing. Chandler opens its leaves well after the early varieties, and a week or two before the very late varieties. This gives three benefits. Spring frost does less damage. There is less walnut blight (a bacterial disease of young tissue), because the young tissue is not exposed to the wettest part of spring. The first generation of codling moth (Cydia pomonella) also does less damage.
- Side-shoot bearing. About 90% of its lateral buds can bear nuts, so you get an early first crop and a shorter wait for your money.
- The kernel. Chandler kernels are extra light in colour. They are the lightest of the major varieties, and they stay light in hot climates as well as cool ones, which not all varieties manage. The kernel is about 49% of nut weight (French records give 47–52%), and it comes out in clean halves, which processors pay more for.
- A tree that fits a modern orchard. Chandler is moderately vigorous and semi-upright, which suits a trained, pruned, machine-harvested orchard. It also sells both as kernel and in-shell, so you do not depend on one narrow type of buyer.
Four weaknesses, from Chandler’s own record
- Young trees are slow to produce side shoots. The 90% figure describes buds that can fruit. In the first three or four years, the tree may not make many shoots to carry them. Feed and water the young trees properly, and this problem mostly disappears.
- The shell is weak in the first bearing years. In the early years, shell strength is only fair, and it improves as the trees get older. Expect a lower grade-out (the share of the harvest that passes quality grading) from your first commercial harvests. Do not judge the whole orchard by those harvests.
- A little kernel tip shrivel in some years. This means that the tip of the kernel shrivels a little. Crop load, heat and water stress while the kernel is filling the shell cause it. Water well through July and August, and it stays minor.
- Chandler does not always shed (release) pollen throughout its own bloom. This is why it needs pollenizers. See the pollenizer section below, and note that the number of pollenizers is smaller than most growers expect.
Both of the published figures for nut size are true. In California, nuts weigh about 13 g per nut, which gives a kernel of about 6.5 g. In French orchards, nuts weigh 9–12 g. Nut size depends on where you grow Chandler and how you manage the crop.
Does your site suit Chandler?
Most sites suit Chandler. Walnuts are grown commercially from France to Chile to Central Asia. Check these numbers before you order trees.
| What to check | Good as it is | Fine, with some preparation | Worth getting advice before planting |
|---|---|---|---|
| Winter minimum | Normal winter lows above −7°C | Winter lows sometimes reach −7 to −9°C. Keep the soil moist in winter, and avoid frost hollows (low areas where cold air collects on still nights). | Lows below −9°C in a normal winter |
| Late autumn cold | No sharp cold before the leaves drop | Occasional lows of −2 to −6°C in late autumn | Regular severe cold before dormancy (the trees’ winter resting period) |
| Spring frost | A slope or open ground, where cold air drains away | Some frost. Chandler’s late leafing helps a lot. | A closed hollow with no way out for cold air |
| Summer heat | Warm summers with irrigation | Above 38°C in midsummer. Plan the irrigation so that the trees always have enough water. | Very hot, with no reliable water |
| Autumn rain at harvest | Dry Octobers most years | Some autumn rain. Choose harvest and drying equipment that works fast enough. | Early, reliable autumn rain every year |
| Spring rain | Dry springs, so little risk of blight | Wet springs. Budget for more protective treatments and for machine access all year round. | — |
| Soil | Deep, well-drained, pH 5.5–7.5 | A hard layer, chalk or wet patches. Fix these problems before you plant. | Shallow soil over rock, or wet all year |
| Water in July | Your water supply covers the peak month comfortably | You can cover the peak month with storage or longer irrigation hours. | Your water supply cannot cover the peak month |
Autumn rain and winter cold in more detail
Autumn rain is the one climate question specific to a late variety. Chandler ripens late. If your autumn rain arrives reliably in early October, the harvest is delayed. Delay destroys kernel colour, and kernel colour is the reason you chose Chandler. In that case, a slightly earlier variety may suit you better, and it is worth discussing before you order.
Winter cold below −9°C in a normal winter is a real limit. Branch and limb damage starts around −7°C in midwinter, and the risk is worse when the soil is dry.
A mature walnut orchard uses roughly 1,040 mm of water a year, plus 5 to 30 percent for the water that your irrigation system loses. Chandler is a productive variety, and productive varieties need water and nutrition in proportion to their yield. Chapter 6, Irrigation, covers water in detail. Chapter 1, Site Selection, explains how to read your soil and water reports.
Pollenizers: plant fewer than you think
Why walnuts need pollenizers at all
A walnut tree carries both male and female flowers, but they usually do not open at the same time on the same tree. In most varieties, the pollen is shed before the female flowers are ready. Chandler is one of these varieties, and its pollen shed does not always cover the whole time that its female flowers are open. So you plant a second variety that sheds pollen at the right moment.
- The wind carries walnut pollen. Bees are not involved. So where you place the pollenizers depends on the wind.
- Walnut pollen dries out and dies quickly. Pollen that is shed far upwind on a hot, dry day will not reach your flowers alive.
Why too much pollen is a problem
Too much pollen makes the female flowers abort. They start to grow, then stop, turn brown and drop, two or three weeks after bloom. Researchers spent ten years looking for a pest, a disease or a nutrient cause. They found that the cause was the pollen itself.
- Flower loss was highest in the rows next to the pollenizer trees, and fell steadily with distance.
- In one orchard, trees more than 122 m from a pollenizer yielded more than 2.5 times as much as trees within 49 m.
- Where growers removed pollenizer trees from a badly affected variety, yields rose by 20 to 86 percent.
How many, and where they go
Plant 5 percent of your trees as pollenizers, whether your block is inside an established walnut district or stands alone. Five percent gives enough pollen to cover the bloom reliably, and it avoids the yield cost of planting too many pollenizers.
If your neighbours already grow walnuts and have good crops, ask them what they do about pollenizers. But the pollen that is already in the air in a walnut district is a bonus in addition to your own 5 percent. It is not a reason to plant less.
Where to put them
- Across the prevailing wind (the wind that blows most often), so the pollen blows through the block rather than along one edge.
- About every tenth row, or about 120 m. The amount of pollen in the air starts to fall beyond roughly 50 m from its source. If the rows are much further apart, the middle of the block gets too little pollen. If they are much closer together, the pollen becomes concentrated where the risk of flower loss is highest.
- In permanent tree positions. If you plan to remove filler trees later (temporary trees planted between the permanent ones), mark the pollenizers. Then you will not remove them by accident at year ten.
- Where you can harvest them separately. Pollenizers bloom at a different time, so they ripen at a different time. If they are scattered singly through the block, it is hard to keep their nuts separate at harvest. In rows that you can identify, this is not a problem.
Which pollenizer for Chandler
| Pollenizer | Leafing | What it gives you | What to be careful about |
|---|---|---|---|
| Franquette our recommendation | Very late | A strong pollen supply and very late leafing, which is useful where spring frost is severe. It is the pollenizer that we supply with a Chandler order, so the whole planting comes from one nursery. | A big tree that needs 12–15 m of space of its own. It is tip-bearing, which means that it bears nuts at the ends of its shoots. Give it that room, and place it where it will not shade productive Chandler rows. Its harvest is also late, and in hot areas it is the variety most affected by branch wilt. |
| Fernette | Later than Chandler | Fernette produces a lot of pollen, bears on side shoots, and comes into production earlier than Franquette. It is a smaller tree that fits more easily inside a Chandler block. We supply it as the pollenizer for Fernor, and we can supply it for Chandler too. | Before you commit a block to Fernette, check its bloom and harvest timing in your own conditions. |
| Cisco | Very late, about a week after Chandler | Cisco is a similar size to Chandler, so there is no shading problem. It has unusually good side-shoot bearing for a late variety, good shell seal and light kernels. It is the name that appears most often in the American records. | We do not produce Cisco, so you would have to get it from another supplier. Its own yield is only moderate, and it is mainly a pollenizer. |
What lateral bearing gives you
Side-shoot bearing is one of the main reasons that growers choose Chandler.
Research shows that side-shoot bearing has little influence on the yield of a mature orchard that is well managed. A variety that bears at the tips can reach a similar yield once the trees fill their space. It only takes longer to get there.
So the benefit of Chandler’s bearing habit comes mainly in the establishment years (the first years after planting). An earlier first crop means a shorter period of spending with no income and a faster payback on your planting investment. This is a large financial benefit, but you get it only if you design the orchard for it.
- Small differences in the percentage mean nothing. A variety listed at 90% is not reliably earlier-bearing than one at 70%. Do not rank varieties by this number.
- Planting density is part of the variety decision. If early production is the benefit, you need enough trees early to get it. Chapter 4, Orchard Design and Tree Spacing, covers that decision and gives the spacings that we recommend.
Chandler needs light inside the canopy (the branches and leaves of the tree). Its fruiting positions are spread along the shoots, not just at the illuminated tips. So shade reduces its yield more than it reduces the yield of a tip-bearing variety.
The flower buds for next year form in June and July of this year. So the light that you allow into the canopy this summer sets your flower number for next summer. Maintenance pruning is not optional on a lateral-bearing variety.
Harvest and drying decide how much quality you keep
Growers most often treat harvest and drying as a separate subject, but they are part of the variety decision. Chandler’s kernel colour is the reason to plant Chandler, and colour is lost in the field, in hours.
Most of the colour loss happens in the first nine hours after the nuts hit the ground. Above 32°C, nuts in the sun lose colour fast. In the shade, the same happens above 38°C. Nuts that are still in their hulls (the green outer covering of the nut) heat up even faster, because the hull holds the heat in. Nuts left on damp ground also develop mould and shell stain, and a stained shell cannot be sold in-shell.
When to harvest
Do not decide by the calendar. The kernel is at its lightest colour when the packing tissue between the two kernel halves has just turned from white to brown.
The problem is that the hull is often not ready when the kernel is. In cool, humid climates the kernel and the hull mature almost together, a few days apart. In hot, dry climates the kernel can be ready up to three weeks before the hull opens. During all that time, quality is falling.
An economic harvest is the time when about 80 percent of the nuts can be shaken off and 95 percent of them can be hulled. In hot inland climates, the economic harvest comes two to three weeks after the kernel is mature. A second shake about a week later removes the rest of the nuts.
So the gap between “kernel ready” and “hull ready” on your site decides how much of Chandler’s colour advantage you can sell. Humid nights and light autumn rain make the gap shorter. Hot, dry autumns make the gap longer.
Drying and storage
Drying
- Dry to 8 percent moisture.
- Never let the drying air go above 43°C. Above that temperature, the oil turns rancid (it smells and tastes bad) and the kernels become inedible. The damage does not show at once. It appears weeks or months later, in storage, at the buyer’s warehouse.
- Drying takes less time later in the season, because nuts left on the tree after the hull opens dry naturally.
Storage
- Walnut is the nut that goes rancid most easily, because of the kind of oil it contains. There is no variety you can choose to avoid this. Breeders have looked and found none.
- Storage is what works. Cold storage at 1–2°C with reduced oxygen has kept kernels in good condition for as long as two years.
- Watch the pellicle, the thin brown skin on the kernel. The pellicle is the kernel’s natural protection, and when it darkens in storage, the shelf life is already getting shorter.
Check your harvest equipment before you decide the size of the block
Calculate the peak tonnes per day that must move from the trees to the dryer on your hottest likely harvest day. Then check each of these machines against that number:
- the shaker (the machine that shakes the nuts loose)
- the sweeper (the machine that gathers the nuts into rows)
- the pickup (the machine that gathers the nuts off the ground)
- the huller (the machine that removes the hulls)
- the dryer.
If the machines cannot keep up with that number, plant a smaller Chandler block. Then spread the rest of the harvest over a longer period. Use a second variety for this, or use your pollenizers, which already ripen at a different time.
Harvest dates that are spread over a moderate period keep your dryer working steadily. But too many varieties make pollination, spraying, harvest, drying, marketing and the separation of each variety’s nuts all harder. Keep Chandler as the main variety, and add other varieties only when each one has a clear job.
Disease: what the variety choice can and cannot do
Disease risk depends on both the variety and your site. The same variety has a different level of risk in a climate with wet springs and in a climate with dry springs.
Walnut blight
What variety choice gives you is avoidance, not resistance. Chandler’s late leafing means that its young tissue is not exposed to much of the wettest part of spring. Californian records describe only moderate blight problems in most districts for that reason. French records, from a climate with wetter springs, describe Chandler as sensitive. Both descriptions are correct. Your own spring rainfall record decides which description applies to you.
- Infection needs free water on the tissue (liquid water on the surface). The length of time that the leaves stay wet (leaf wetness) matters more than the total amount of rain.
- The bacteria survive the winter inside next season’s buds and catkins (the male flowers), so they are already in the canopy when growth starts. Cleaning up the orchard alone will not remove them.
Budget for the treatments. In areas with dry springs, growers commonly need only one to three protective treatments a year. In areas with wet springs, three to six or more is normal. That difference roughly doubles a recurring annual cost for the life of the orchard, so you should include it in your planting budget. Ask your local agricultural adviser what is registered where you are. This differs in every country.
Also make sure you can get a machine into the orchard in a wet spring. A grass or strip orchard floor gives your machines firm ground when the soil is soft and you need to apply treatments. On a site with some frost risk, the opposite argument applies. Bare, cultivated soil warms up and gives the heat back better on a frost night. Choose according to which risk is larger on your land.
Other diseases and problems worth knowing about
| Disease | What it means for your variety choice |
|---|---|
| Anthracnose | French records list Chandler as sensitive. Our main source, from California, does not cover this disease at all. If you are in Europe, Turkey or another region with humid summers, treat anthracnose as a real question and get local advice on it. |
| Trunk cankers (dead areas of bark) | Deep bark canker is mainly a Hartley problem, not a Chandler one. But the disease enters through deep wounds, and mechanical harvesters make deep wounds. A harvester injury stays open to infection for about ten days, and dirty shaker pads carry the bacteria from tree to tree. Keep shaker pads clean and in good condition. |
| Blackline | Blackline is a virus that is carried in walnut pollen. Once the virus is inside an English walnut tree, it moves slowly downward. When it reaches the graft union (the joint low on the trunk where the variety was grafted), the tissue there dies. A black line forms, the ring widens, and in the end the top of the tree dies. If blackline is present in your district, do not look for a resistant variety. Build an orchard that earns back its cost early instead. Plant the trees at good density, and use an early-bearing variety that bears on its side shoots. Then the orchard will have earned its establishment cost well before decline starts. This is an argument for Chandler on a blackline site. When you replant into infected ground, look at a pollination chart. A later-blooming variety can miss the pollen shed of infected neighbours, because the virus spreads only during the short pollen-shedding window. |
| Codling moth (Cydia pomonella) | Early-leafing varieties are fully exposed to its first spring generation. Late-leafing varieties, Chandler among them, largely avoid it. That is a recurring annual saving. |
| Hull behaviour | This is a real difference between varieties, but it rarely appears in catalogues. In some varieties, the hulls open wide and expose the nut before harvest. In others, the hulls only become loose around the nut. Exposed nuts are more attractive to insects that bore into the nut, but less prone to mould because the wet hull comes away. Ask which behaviour the variety you are considering shows in your area, and choose the variety whose behaviour fits the larger risk on your site. |
When a different variety makes sense
Chandler should normally be the main variety. Other varieties belong in the plan when they have a clear job.
| The job | Varieties to consider | What to know |
|---|---|---|
| Pollenizer for Chandler | Franquette, Fernette | See the pollenizer table above. Franquette is our recommendation and needs 12–15 m of space of its own. Fernette is the smaller alternative. |
| Severe spring frost | Franquette, Fernor and other very late varieties | Later leafing avoids more frost, but the harvest is later and the trees are usually bigger. Fernor is a variety we grow and recommend for high-altitude and frost-prone sites. |
| Spreading the harvest across your equipment | Tulare and other mid-season varieties | Tulare is the strongest of this group. It has good side-shoot bearing and light kernels, and its kernel is 53% of the nut weight. We grow it. Earlier varieties make the harvest more convenient, but they are more exposed to blight and codling moth. |
| Very large in-shell nuts | Howard | A variety we grow. Be careful: as a general rule, big nuts come with a drawback. Several of the very-large-nut varieties come into leaf early, which is a poor choice where late frost and spring rain are likely. |
| An in-shell contract with a traditional buyer | Hartley | Not a variety we produce. It has long been the classic in-shell variety, and it has good colour. But it bears at the tips, comes into production slowly and needs 9–12 m spacing. It is also by far the most exposed variety to deep bark canker. It needs deep, fertile, well-drained soil and good irrigation. |
| Local adaptation | Regionally trialled Turkish, Balkan, Italian, Spanish or French material | Where local trial data exist for your climate, they matter more than any figure in this chapter. Use them. |
Two cautionary examples
Neither of these is a candidate. Each one teaches something about how to read a variety table.
- Serr looks excellent in the numbers: a large nut, a kernel that is 57% of the nut weight, and strong demand. But it fails because of flower abortion, and it sometimes loses more than 90 percent of its female flowers. Serr should be planted with no pollenizers at all.
- Chico has the highest side-shoot bearing figure of any variety, at 96 percent. Even so, processors lost interest in it. The nut is small, the kernel is hard to remove whole, and only 60 percent of kernels are light. Its early bloom also makes it very exposed to blight and codling moth.
Mistakes worth avoiding
Reading the numbers
- Reading the lateral-bearing percentage as a forecast of mature yield. Lateral bearing gives you earlier production. Design your density plan to get that benefit, and do not rank varieties by the number.
- Copying a calendar date from another country. Copy the gap between varieties instead, and check it against a variety that is already growing near you.
- Choosing a thin shell or a high kernel percentage without asking your buyer. Get the specification in writing before you plant.
Planning the block
- Planting 10 percent pollenizers because that is the traditional number. Plant 5 percent.
- Buying pollen to improve nut set. Never do this.
- Assuming late leafing fixes a frost hollow. It helps a great deal. It does not turn a closed hollow into good ground. You need both the right place and the right variety.
- Planting more of one variety than your dryer can handle. Plan your equipment first, then the size of the block.
Before you order trees
What to have in front of you
- Your winter minimum temperatures and your late-frost record.
- Your autumn rainfall pattern for the weeks around harvest.
- Your spring rainfall and leaf-wetness pattern, and a realistic budget for protective treatments.
- A soil report by depth and a water report, read together, and your July water figure.
- Whether blackline, crown gall, oak root fungus or nematodes are present in your district.
- Your pollenizer variety, the percentage (5%), and a map showing wind direction, rows and permanent tree positions.
- Your planting density and your irrigation design.
- Your buyer’s written specification: kernel colour class, halves, size, moisture, in-shell or kernel, delivery date.
- The peak tonnes per day that your harvest and drying equipment can really handle.
Summary
Plant Chandler, unless something specific on your land is a reason to choose another variety. It gives you early production, the lightest kernels on the market, clean halves, and buyers in both the kernel and in-shell trades.
Plant fewer pollenizers than the old advice says. Make 5 percent of your trees pollenizers. Put them across the wind, about every tenth row, in permanent positions where you will not remove them by mistake.
Plan your harvest and drying equipment before you decide the size of the block. Chandler’s kernel colour is worth money only if the nuts reach the dryer in the first hours after they hit the ground. The drying air must also never go above 43°C.