Organic Gardening Tips and Methods Ornamental Trees (Part 10, Section 2) Propagation Raising Trees from Seed; Tree species may be propagated from seed as their seedlings usually retain the distinctive characteristics of the parent plant, hybrids and cultivars rarely come true to type. Raising a tree from seed is a relatively simple process, it is however, a slow method, if a tree is being grown mainly for its flowers (or fruit), as the tree will take a number of years to reach flowering (or fruiting) size. Extracting Seed; The protective covering of some seeds should be removed first, the method for this varies, depending on the type of seed coat, the coating on winged seed may be removed simply by rubbing it between finger and thumb, some cones disintegrate naturally and the scales may then be separated, place pine and spruce cones in a paper bag and keep them in a warm, dry place until the cone scales open and shed the seed into the bag, immerse cedar cones in hot water and leave them to soak until the scales open. The method of extracting seed from fruit or berries depends on the seed size and type of flesh, large fruits such as those of crab apple (Malus), may be cut open and the seeds extracted, smaller fruits such as those of Sorbus, in warm water for several days, viable seeds will sink in water, discard any floating seeds, pick the remaining flesh off the viable fruits so that the seed is clean. Storing; Once the seed has been extracted, dry it if necessary and place in a sealed and labelled plastic bag, if planning to sow the seed within a few days, store it at room temperature, for longer-term storage, keep it on the top shelf of a refrigerator so that it is cool but not frozen. Breaking Seed Dormancy; Some seeds have a natural period of dormancy to prevent germination adverse climate conditions which would threaten the survival of the seedlings; this has to be overcome before the seed will germinate. Several kinds of dormancy occur, sometimes combined, which vary according to the species, most commonly, dormancy is achieved either by a hard, thick seed coat which prevents water being taken up, or by a chemical inhibitor, which delays germination until there is a significant temperature change. In most cases dormancy can be broken artificially by wearing away the seed coat or by chilling the seed. Scarification; Before sowing seeds with an impermeable coating, scarify them to allow germination to occur, large seeds with a particularly hard covering, such as; oaks (Quercus), may be nicked with a sharp knife, or a section of the seed coat filed away to let in moisture, smaller seeds that are not easily nicked, such as those of pines, may be shaken in a jar that has been lined with sandpaper or partly filled with sharp grit, or they may be filed individually (by hand) with an emery board (which can take some time). Seed from legumes, for example; Acacia and Robinia, should be left to soak in a container of hot water for approximately 24hrs in a ratio of; three parts hot water to one part seed. Stratification; Dormancy in seed from trees from temperate climates is commonly overcome by chilling or “stratification”, seed may either be sown outside so that it is chilled naturally during winter, or more reliably, stratified artificially by being stored in a refrigerator. If refrigerating seed, first mix it with moistened vermiculite, peat-substitute, or peat, place it in a clear plastic bag, then seal the bag and put it in a refrigerator (making sure you have labelled the bag), check the seed regularly through the unopened bag, it should be sown as soon as there are signs of germination. The length of chilling time required varies considerably, as a guideline, many deciduous species require six to eight (6-8) weeks of chilling at 0.1-1 degrees C (33-4 degrees F), while conifers need only about three weeks, some seeds only germinate after they have been sown and once chilling has ceased, in such cases, sow batches of seed at intervals, for example; after four, eight, and twelve weeks of chilling, as this should ensure that at least some seeds germinate. Sowing Seed in Containers; This is a simple way of raising a small number of seedlings. Thoroughly clean any work surfaces and containers to be used before sowing the seed as to avoid contamination from soil-borne pests and diseases, first, fill the pots, containers, pans, or seed trays with compost up to the rim, large seeds or those that produce seedlings with long tap-roots such as oaks (Quercus), should be sown about 8cm (3in) apart in deep single or multi-celled seed-trays or in flexible root trainers using a presser board, press the seeds into un-firmed compost, then cover them to their own depth with compost and firm to about 5mm (1/4in) below the rim. Sow very large seeds, for example, those of horse chestnut (Aesculus) singly 10-15cm (4-6in) pots; insert the seed in firmed compost so that just the top of the seed is exposed above the surface. Small seeds for example, those of Sorbus, may be scattered evenly, or if sufficiently large, individually pressed into prepared pots or trays of firmed compost, they should then be barely covered with sieved compost followed by a layer of grit 5mm (1/4in) deep, after sowing, thoroughly water all seeds from above, then label, place the containers in a cold-frame or within a greenhouse/glasshouse, in a closed propagation case or under a pane of glass. Temperate species are best kept at 12-15 degrees C (54-9 degrees F), and warmer temperate and tropical species at 21 degrees C (70 degrees F) to stimulate germination. Once the seeds have successfully germinated, spray them periodically with a fungicide to discourage damping-off. Pricking-Out; When the seedlings are large enough to be handled by their seed leaves, prick them out so that they have more space to grow, this may be done by knocking the container sides to loosen the compost, and then lifting and transplanting the seedlings into individual pots, alternatively, remove all the seedlings and compost together from the container so that the seedlings may be separated with minimal root disturbance, after transplanting, firm the compost gently around the seedlings, then level it by gently tapping the pot on the work surface. Aftercare; Water and label the seedlings, and keep them out of direct sunlight in a temperature similar to that needed for germination, until established, gradually harden them off over a few weeks, feeding them regularly and spraying them with a fungicide. Do not over water, but make sure that the compost does not dry-out, once hardened-off, they may be planted out in open ground or larger pots/containers if there is no danger/risk of frost. Sowing Seed Outdoors; If raising a large number of seedlings, seed may be sown in an outdoor seedbed, with this method, the seedlings require less regular attention and their growth is less restricted than if sown in containers, but a special bed must be prepared, if possible, do this a few months before sowing by thoroughly digging the area to a “spit-deep”, incorporating organic matter and some coarse grit, keep the ground clear of weeds. When ready to sow, rake the soil down to a fine tilth, then broadcast small seeds or station sow larger seeds individually, lightly rake over the seeds, cover the bed evenly with a 0.5-1cm (1/4-1/2in) layer of grit, and firm with a presser. If the soil is at all dry, water thoroughly, then label with the plant name and sowing date. In exposed sites, young seedlings may need t be protected with wind-beak netting, or with a floating cloche, if the seeds are well spaced, disease should not be a problem and the seedlings may be grown on/in situ for twelve months before being pricked-out, water the seedlings as necessary and heck them regularly in case treatment is needed for pests such as greenfly and red spider mite. Layering; Layering may be used to propagate hybrids and cultivars as well as species, this method of propagation occurs naturally in some plants, when a low-growing stem roots itself in the ground, once this happens the stem may be removed from the parent plant and grown on. Air-layering is where the shoot remains above the ground, may be used for trees with low-growing stems, the advantage of layering is that the layered stem needs very little attention while the roots become established. It is a slow method, however, because in order to obtain suitable material the plant must be prepared a year in advance and the layered stem may take a year or more to root. Simple-Layering; In this method, a shoot is pegged down into the ground until it has rooted and is then cut off from the parent plant. Prepare the parent plant a year before layering is to take place, in late-winter or early-spring, prune a low branch to stimulate new, young shoots that will root easily. In early spring, the following year, select a vigorous shoot and make a small wound 30-45cm (12-18in) from the tip, brush this with hormone rooting powder to encourage rooting, add plenty of leaf mould or similar organic matter and sharp grit to soil where the shoot touches the ground and peg it down into a shallow hole, tying it to a vertical cane, backfill the hole and firm the soil well, leaving the shoot tip exposed, then water thoroughly and if necessary, protect the shoot from rabbits and other animals with wire netting, about 12 months later, check to see whether the shoot has rooted: if it has, sever it from the parent plant and either plant it in open ground, or pot it up, if it has not rooted, leave it in place and check it again about a month or so later. Air-Layering; The principle of air-layering is the same as simple-layering, except that the layered shoot roots above the ground rather than in it, in spring, select a strong stem that ha ripened in the previous year and remove any leaves 30-45cm (12-18in) behind the growing tip, prepare the stem either by cutting a tongue 5cm (2in) long in the bark 22-30cm (9-12in) behind its tip, or by removing a 6-8mm (1/4-3/8in) wide ring of bark from the stem, at this point, in either case, brush the wound with hormone rooting powder. Surround the cut stem with a moist rooting medium and seal it in, to do this, first make a plastic sleeve by cutting off the sealed end of a plastic bag, and then; slide it along the stem until it surrounds the cut, and secure the lower end with string or tape, moisten some well-aerated rooting medium (such as sphagnum moss, or a mix of equal parts of; peat-substitute or peat and perlite), then use it to wedge open the tongue, add more medium around the stem inside the sleeve and seal the top, if they layer has rooted by the next spring, sever the stem from the parent plant, remove the sleeve and pot on, if not rooted, it should be left in place for another year (until the following year/season). Tree Seeds Requiring Stratification; • Acer (some), • Betula, • Carya, • Fagus, • Sorbus, Trees to be Layered: Simple-Layering; • Cercidiphyllum, • Chionathus retuses, • Corylus, • Davidia, • Dipteronia, • Eucryphia, • Halesia, • Hoheria lyallii, • Laurus, • Magnolia cambellii, • M, grandiflora, • M, obovata, Air-Layering; • Ficus *, • Magnolia grandiflora, • M, “Star-Wars”. Note; Symbol * = Non-Hardy All Information given coincides with the guidelines of The Royal Horticultural Society (RHS).
Posted on: Wed, 13 Aug 2014 10:01:32 +0000
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