RAISE & SAVE
name of the plant and the date of collection. Store in a cool, dry, airy place but do not subject seed to frost. Seeds can also be stored in a refrigerator at a temperature of 1-5°C but must not freeze. I find that the seed of acers (maples), fraxinus (ash) and fagus (beech) keeps better if it is mixed with slightly moist peat, placed in polythene bags and stored in a fridge at 1-5°C. This method prevents the seeds drying out.
■ Stratification
Fleshy fruits and berries, such as those of cotoneaster, berberis, holly, sorbus (mountain ash), malus (crab apples) and prunus (ornamental cherries etc) need to be stored by a method known as stratification. This softens the hard seed coats and results in quicker and better germination when the seeds are sown.
When you have gathered berries and fruits, macerate them to expose the seeds – spread them out on a bench or table and crush with a block of wood. It does not matter whether or not you separate the seeds from the pulp, but if you do want to separate them, place the whole lot in a tin of water for a few days. The pulp and light non-viable seeds will float; the viable heavy seeds will sink to the bottom. The water and pulp can then be drained off.
The seeds (or seeds and pulp) are then mixed with one to three times their own volume of moist sand, and the mixture placed in tins with drainage holes in the base, or in pots. A 1in (2.5cm) layer of sand can be placed on top. Alternatively, single layers of seed can be placed between 1in (2.5cm) layers of moist sand in containers, finishing with a layer of sand on top. Label the container.
Place the containers of seed in a cold, preferably northern, aspect outside to subject them to alternative freezing and thawing. Protect from birds and rodents. This stratification process will soften the hard seed coats and may last 6-18 months, depending on the species (see table opposite). After stratification, the seeds and sand are sown together.
■ Direct sowing
Seeds of some species, such as horse chestnut, oak and sweet chestnut, are best sown immediately after harvesting in autumn. However, most tree and shrub seeds can be sown outdoors in March or April.
Prepare the seed beds beforehand by digging over the soil to the depth of a fork. If the ground is not well drained, make raised beds, about 3in (7.5cm) high. This will ensure better drainage. The surface of the bed should be firmed by treading and raked to produce a fine tilth. It helps to rake a general-purpose fertiliser at 105g per sq m (3oz per sq yd). Sow thinly in drills across the bed, spaced 6in (15cm) apart.
Drills can be ¼-1/2in (0.5-1cm) deep, according to the size of the seed – small seeds should be sown less deeply than large ones.
After sowing, cover the seed with fine soil or, preferably, with a layer of pea shingle as this prevents the surface of the bed drying out quickly in warm weather.
Keep the seed bed moist and shade the seedlings from hot sun. The seedlings should remain in their beds until October or November, when they can be lifted with a fork. Then they can either be lined out 12in (30cm) apart in nursery beds to grow on, or you can plant them in their final positions in the garden.
■ Sowing under glass
The seed of some trees and shrubs is sown in containers and germinated in a heated greenhouse or frame. Very fine or small seed, such as that of rhododendrons and hypericums, is best treated in this way. Other seed germinates better in warmer conditions, particularly that of camellia.
Use pots or seed boxes, depending on the amount of seed to be sown. Place a layer of crocks (broken clay pots) in the bottom to assist drainage, and cover with a layer of roughage such as coarse peat. John Innes seed compost can be used for many subjects, but for ericaceous species like rhododendrons, azaleas, ericas and camellias, use pure moist sphagnum peat.
To ensure you sow dust-like seed thinly and evenly, mix it with an equal amount of fine dry silver sand. Sow a light scattering of the seed/sand mixture on the surface of the compost and you should have a thin, even distribution of seed. Large seeds, such as those of cytisus, can be spaced out evenly by hand, about ½-3/4in (1-1.5cm) apart each way. Very fine seed like that of rhododendron should not be covered with compost as this will inhibit germination. Larger seeds should be covered with a layer of compost equal to the diameter of the seed.
Stand the sown containers in water until the surface becomes moist, drain and stand on a bench in a greenhouse or frame. The containers may be covered with glass and paper. Turn the glass each day to prevent condensation dripping onto the compost, but keep the compost moist. Once the seed has germinated, remove the glass and paper and give maximum light.
As soon as the seedlings are large