Vegetative propagation

Vegetative propagation by suckers, cuttings or layers is used for some species. These include the following:

Table 5e: Table of species and possible methods of vegetative propagation

• Species which rarely set viable seed in this country
• Particular cultivars of species whose characteristics can only be maintained by vegetative reproduction.
• Species which are easier and quicker to propagate vegetatively.

Suckers

Some trees and roots have shallow roots which produce separate plants, called suckers. These can be separated from the parent tree by cutting through the roots around the sucker. It’s easier to take small suckers, under about 60cm (2ft), than to attempt to detach larger plants. Keep the plant roots moist and follow standard planting advice (Chapter 6 – Planting and protection).

Hardwood cuttings

These are taken from wood that is fully matured, or hard. Species that can be easily propagated from hardwood cuttings include willow, poplars (other than aspen), dogwood, hazel, honeysuckle and elder.

1. Take cuttings from mid-October to December. From the previous season’s growth, choose well-ripened dormant shoots with nodes, which are the swellings that mark the position of buds. Avoid shoots that are ‘blind’, or lack buds. Cuttings should be at least as thick as a pencil, although willow cuttings can be thinner. Some plants root better if they are taken with a heel. Poplar and willow should be unheeled.
   
2. Cut the shoots into sections 15-30 cm (6-12”) long, with at least three buds to each section. Make the top cut sloping, at 3cm (1”) or less above the top bud, and the lower cut straight across just below the bottom bud. The sloping cut allows water to run off. Unless the cutting is left with a heel, make the cuts as clean as possible using bypass secateurs, with the blade side on that of the cutting, so that the waste, not the cutting, is bruised.
3. Choose a site in the nursery which is sheltered from cold winds, preferably in a sunny, south facing situation where the soil will warm up quickly in spring. The soil must be well-drained, or the cuttings will rot. Drainage can be improved by placing coarse sand in the base of the V-trench before the cuttings are inserted. If conditions are very poor, with frozen or wet ground, the cuttings can be sealed in a plastic sack and stored at about 4.5˚c in a shed or garage for a few weeks.
4. Space the cuttings 30-37cm (12-15”) apart, in rows 37-45cm (15-18”) apart, inserted to about two-thirds of their length. Tread well round the stems to firm the soil. check at intervals to make sure cuttings are still firm, and have not been lifted by frost.
   
   Plants should be ready for transplanting to their final planting position at the end of the second growing season.
5. Cuttings  of honeysuckle are best rooted direct into containers of compost and sharp sand or perlite. Provide a cane for support. Growth should be rapid, and plants can be planted out after a year.

The following points apply to poplar and willow cuttings only:

6. By late spring, the cuttings will have produced two or more sprouts at least 15cm (6”) long. cut off all but the strongest sprout on each plant.
7. At the end of the first growing season, cut the plant back to 3cm (1”) above ground level to promote a better root:shoot ratio. leave at least one bud on the stem.
8. Transplant to final positions at the end of the second growing season.

Direct planting of willows and poplars

Willows and poplars root easily from cuttings, which can be inserted direct into the final planting position. Take cuttings from vigorous one-year-old shoots, preferably from coppice growth. Cuttings from mature trees do not root so quickly. The cuttings should be 20-25cm (8-10”) long, with the top cut made about 1cm (half an inch) above a bud, and the bottom end just below a bud. ‘Sets’ are cuttings about 2m (6’) long, taken from one- or two-year- old wood, used in the commercial planting of willows and poplars for timber, but all cuttings of willow and poplar for direct planting are commonly referred to as sets.

Cuttings or sets must have good contact with the soil in order to root well. In deep, cultivated soil, the cuttings or sets can simply be pushed into the soil, leaving about one- third protruding. In heavier soils this would damage the cuttings, and you will need to make a hole with a crowbar or similar. Depending on the size of the tool, you may need to backfill the hole with friable soil or sand to make sure there is no air pocket around the cutting. Note that cuttings and sets should receive the same attention to weeding as rooted plants (Chapter 7 – Aftercare).

Layering

Some shrubs (see Table 5e at the top of this page) spread by side shoots which bend down and root where they touch the ground, forming a new but still connected plant. These species can be layered by pegging a shoot to the bare ground and covering it with soil. Once the shoot has rooted it can be separated from the parent plant by cutting through the shoot. The layer is then left for another season to establish itself before being transplanted.

Nursery soil fertility

It’s important that the structure, organic content and fertility of the nursery soil is maintained if trees are going to be grown on the same site for many years.

Nursery soils must be light for ease of working, but this means they are hungry soils. Regular addition of organic matter will help maintain fertility and moisture-holding ability.

Good structure is maintained by avoiding cultivation in wet weather, and avoiding the trampling of beds. The addition of organic matter in the form of leaf mould, compost or well rotted farmyard manure will help maintain structure and water holding ability, as well as contributing to fertility. Avoid the use of peat. Organic matter can be added in the autumn or spring, when the beds are cultivated. A mulch spread over the transplant beds will help retain moisture and keep down weeds, and will become incorporated into the soil during the season.

Tree nursery soils must contain sufficient nutrients including nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (ca) and sulphur (S). For most species, a soil pH in the range 5.5 to 7pH is suitable. Soil testing kits for pH and N, P and K are available from garden centres. Soils can be made more acidic by the addition of sulphur chips, which are available from garden centres.

Most commercial nurseries use inorganic fertilisers, in the form of soil dressings or liquid fertilisers applied to the trees in growth. For full details, see Forest Nursery Practice (Forestry Commission, 1994).