Pecan and Heartnut: Exotic Nut Trees for the Climate-Change Garden

Nut trees from distant climates sound like an adventure in your own garden. The pecan from the American South, the heartnut from the mountain forests of Japan: both now show up in nursery catalogues as "climate-change winners". That is half true, and it deserves an honest look before you dig a hole and wait a decade.

Why exotic nut trees at all?

Summers are getting longer and warmer, winters milder. That brings species within reach that had barely a chance in Germany thirty years ago. That is the tempting story. The truth is a little more awkward: a single hot summer does not make a growing region, and the decisive question is not whether the tree survives, but whether the nuts ripen reliably.

This is exactly where pecan and heartnut part ways. One depends on summer heat, the other on winter hardiness. Anyone who lumps them together will be let down by at least one. It always helps to compare against the tried-and-tested walnut, which crops reliably across almost all of Germany and sets the benchmark for everything exotic.

The pecan: tempting, but impatient

The pecan (Carya illinoinensis) comes from the river bottoms of Mississippi and Texas. It is closely related to the hickory and loves what its homeland offers: long, hot summers with plenty of heat hours and deep, moist soils. The kernel is milder and oilier than the walnut's, almost buttery. No wonder so many people dream of it.

The catch lies in the climate. The pecan needs considerably more summer heat than the walnut to fill out its nuts. In wine-growing areas along the Upper Rhine, the Mosel or in sheltered city locations, it can succeed in good years. In an ordinary garden in northern Germany, in the uplands or in a frost pocket, the tree will grow, but you may wait in vain for filled nuts.

Never buy a seedling if you are hoping for a crop. Only grafted, north-adapted varieties with a short ripening time have a realistic chance in our climate. Names like 'Carlson 3', 'Kanza' or 'Lucas' come up among enthusiasts because they ripen earlier. Even then the rule holds: you are planting for the future, not for the year after next.

The heartnut: the underrated Japanese

The heartnut (Juglans ailantifolia), more precisely the variety cordiformis, comes from the mountain forests of Japan and is the more honest recommendation. It is a close relative of the walnut, but with two advantages: it is remarkably hardy, often to around minus 30 degrees, and its heart-shaped kernels come out of the shell almost intact. The flavour is mild and sweet, without the bitter note of some walnuts.

Visually it is a spectacle. The pinnate leaves grow huge, almost tropical, giving even young trees an exotic character. It does, however, leaf out late, which protects it from late frosts, and carries its nuts in decorative clusters. For gardens with a harsh climate, where the pecan would stand no chance, it is often the better choice.

The heartnut is partly self-fertile, but crops much better with a second seedling or a walnut nearby. Its flowering, as with all members of the walnut family, is slightly staggered between male and female, and a second tree evens that out. If you only have room for one tree, you will still get a harvest, just a more modest one.

Position, soil and space requirements

Both trees have clear demands, and both grow large. Underestimate the space they need and you will regret it in twenty years. Reckon with a tree that can reach twelve to over twenty metres and develop a broad crown. For a small terraced-house garden that is often a size too big, but for a meadow orchard, a large garden or an allotment club site it is ideal.

A word on soil: both species like even moisture but tolerate no waterlogging. If your garden is heavy and loamy, a generous planting hole with worked-in sand and compost helps. On pure sandy soil you will need to water during dry spells, otherwise the thirsty pecan in particular suffers.

How to plant a young nut tree

Nut trees dislike being moved; the taproot takes it badly. So plant once, and properly, ideally in autumn or early spring when the ground is not frozen. Container stock can be set almost year-round, bare-root trees only during dormancy.

1. Fix the spot for good

   Measure the distance to boundaries and buildings and picture the fully grown tree. A nut tree stays where it is planted.

2. Dig a generous planting hole

   Twice as wide as the root ball, and loosen the soil at the base well so the taproot can find its way down.

3. Set the tree, not too deep

   The graft union stays above the soil, the root collar at ground level. Planted too deep, the trunk rots.

4. Water in and mulch

   Water in thoroughly, then lay down a mulch layer. It holds moisture and suppresses competing weeds.

5. Stake and guard

   A support stake against wind, a collar guard against voles and browsing wildlife. Young nut trees are a popular snack.

Honest assessment: who is it worth it for?

Now the honesty I promised. Neither pecan nor heartnut are trees for people who want a full basket quickly. Both need years before they crop, and the pecan additionally needs a climate that most German gardens simply do not offer. If you want to harvest reliably and soon, plant a walnut or a hazelnut and you will be happier.

And yet there are the right candidates. If you live in a wine-growing area, enjoy experimenting and have the patience for a decade of lead time, the pecan is a fascinating project. If your garden is harsh and cold, but you still want something special, the heartnut is the wise choice, tougher than any pecan and with the finer foliage into the bargain. For everyone in between, the walnut remains the sensible standard, and if you prefer something smaller, the Turkish hazel or the sweet chestnut make intriguing alternatives.