An open ground seedbed is best for tree and shrub seedling propagation. Although it is quite possible to sow seeds in seed trays or pans (dwarf pots) containing compost, the quality of the compost will inevitably deteriorate and germination may be impaired after a considerable time outdoors. After germination, the seedlings should be left to establish for a growing season before transplanting, and the restrictive volume of a seed tray or pan may not allow adequate space for root or seedling development. Another drawback is that more day-to-day management is required for seedlings in seed trays and pans to ensure that watering is not sub-standard and that the seedlings have adequate nutrients.
The advantage of the open ground seedbed is that it is self-sufficient and encourages unrestricted growth of seedlings. Nor does it need to be extensive as most seedlings can be intensively grown on a relatively small area: oaks and chestnuts at ten to twelve plants per square foot; magnolias at 25 plants per square foot; and conifers at 50 to 70
plants per square foot.
The root system of many trees and shrubs is modified to live in association with a fungus that fulfils many of the functions of the root in exchange for food: this association is often obligatory on the plant and is necessary from an early stage for normal development. It is therefore important to ensure the presence of these fungi in the seedbed at germination, and leaf mould is a good source.
The preparation of the seedbed should be carried out in winter so that the soil can be left rough and allowed to weather. In order to improve drainage, soil conditions, seed covering and ease of seedling maintenance, the level of the seedbed should be raised above the surrounding soil. Set up boards 8r-9 in high round the proposed seedbed. Keep the width of the seedbed relatively narrow (say 3 ft) so that seeds can be sown evenly across it. At this width, covering the seeds and general maintenance is much easier.
1 Erect side boards round proposed seedbed and fill in with soil.
2 Shovel peat and leaf mould over entire seedbed. Add grit if soil is heavy.
3 Dig seedbed thoroughly to a spit deep. Leave over winter to weather.
Thoroughly dig the seedbed with a spade to a spit deep, incorporating peat and, if possible, leaf mould. If the soil is particularly heavy, also add grit.
In spring, knock the seedbed down to a rough tilth. This encourages weed seeds to germinate. These can then be sprayed or hoed off, so reducing the problem of weeds later on.
Prior to sowing, rake in a phosphate fertilizer at the rate of 4oz to the square yard. Ensure the seedbed is level in order to facilitate sowing, and more especially seedbed watering. It also makes the depth of seed cover more easy to assess.
The process of germination in tree and shrub seeds, as with any other seeds, should be encouraged to take place as quickly as possible so that the best use can be made of the available food reserves. Thus, tree and shrub seeds should be sown under the best possible conditions in a well-drained, aerated seedbed with sufficient supplies of water and a warm environment.
Germination is primarily dependent on water, and the seed must swell and become completely imbibed before biological activity can begin. After this stage, water is still all-important as it forms the basis of all living processes causing germination. The seedbed, however, must not become waterlogged. Air, which contains oxygen, is also essential around the seed. Energy is necessary for growth, and it is produced when oxygen is used in the breakdown of the carbohydrate reserves of the seed. Thus, if conditions reduce available oxygen, germination is retarded.
The other major factor that affects germination is temperature. All growth processes are chemical reactions and as such their rate is a function of temperature: the warmer the conditions, the faster the reaction. Thus the rate of germination is directly affected by the seedbed temperature, and it is best to sow seeds when soil temperatures are warming up in the spring.
4 Break down the soil to a rough tilth in spring.
5 Encourage weeds to germinate. Then spray with weedkiller or hoe them off.
6 Rake in a phosphate fertilizer. Level soil down to a fine tilth.
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