Sweet chestnut

Mature sweet chestnuts are fully hardy and need no winter protection in the lowlands of Germany, Austria and Switzerland. Only in the first one to two years in place does it help to cover the root zone with a thick layer of leaves or mulch and to wrap the young trunk in horticultural fleece until the tree is established.

Sowing is the simplest method for rootstocks or natural woodland trees, but it does not give you fruit true to type. Collect ripe chestnuts directly from the tree in October (no nuts lying on the ground or damaged by pests), remove the spiny husk and store the seeds layered in sand, cool and moist (about 0 to 10 °C), for several weeks so that they neither dry out nor go mouldy. This cold stimulus (stratification) is important for reliable germination. Before spring sowing (April/May), soak the seeds for 24 to 48 hours in lukewarm, low-lime water. Push each chestnut, flat side down, a few centimetres deep into a loose, rather low-lime seed compost. Keep the soil evenly moist; the first seedlings appear after a few weeks. In the second year, prick out the young plants into deep pots.

Grafting is the only way to pass on a particular variety true to type. One-year-old seedlings of Castanea sativa (well adapted to the Central European climate) or vegetatively propagated hybrid rootstocks (C. sativa × C. crenata), which can bring more vigour and disease tolerance, serve as rootstock. Suitable grafting forms are bark grafting (May, when the bark “runs”), cleft grafting (spring, shortly before new growth) and budding (early summer onto a growing bud, with better success rates than summer budding onto a dormant bud). Cut the scion in winter and keep it dormant until then (cool, not drying out). Take care to make clean, smooth cuts and secure unions with grafting tape. Incompatibilities between rootstock and scion can occur especially with hybrid combinations and may only show after years.

Layering/mounding suits hobby gardeners who want to obtain clonal young plants without grafting. For layering, in spring you bend a flexible young shoot in an arc to the ground, wound the underside lightly with a knife, fix it with a ground anchor and mound moist soil over it, leaving the shoot tip vertical out of the soil. For mounding, you cut the mother plant back to a stump and in spring mound soil over the newly sprouting shoots from the base. After one growing season, roots have formed; you can then separate the rooted shoots in autumn or the following spring and plant them out. This method gives genetically identical plants; true-to-type varieties, however, depend on you using a known mother plant that is true to type.