Propagating Plants – Alpine Garden Plants
Alpine Plants from Seeds
Probably the most exciting part of gardening is producing new plants and growing alpines is no exception. Many may be reproduced by very simple means; the easiest and best method tois to grow them from seed. Unfortunately, few companies sell alpine seeds but those who do, are well worth contacting. Alternatively you could join the Alpine Garden Society or the Scottish Rock Garden Club, both of which issue large annual seed lists to their members and will give excellent advice.
Alpine seeds come in a variety of shapes and sizes, each requiring a different method of sowing. Large seeds like Sorbus are sown individually, whereas very fine dust-like seeds such as Haberleas can be mixed with dry sand to make sowing more even and feathery seeds like those of the Pulsatillas are teased out and flattened on the surface of the sowing medium. Seeds of an average and manageable size can be sown straight from the packet or by dropping them from a folded sheaf of paper.
Seeds may be sown in a variety of containers but porous clay pots are probably the most satisfactory. Place a crock over thehole, if it is large enough to lose through, and fill the container with a soil mixture to within 2.5cm (1 inch) of the rim (when firmed down) for large and feathery seeds, slightly higher for small ones. Sow the seeds and cover with 5mm (1/4in) of pea gravel or shingle: a single layer for the finer seeds, slightly more to hold down the larger and feathery seeds. The sown seeds must lie thinly, otherwise when they have germinated their roots will entangle, making separation difficult, and causing damage which may destroy the plants.
Use a gritty soil mix; equal amounts of John Innes seed compost and grit or fine shingle, which must be acidic for all acid-loving plants.
No heating is required to germinate alpine seeds and, apart from during wet weather, no frame cover either, butthe pots in coarse sand or grit will reduce the need for watering. The shingle layer over the seeds prevents heavy rain dislodging the seeds from the pots.
Place the containers in a cool place out of direct sunlight, in an open frame until germinated. Then cover the pots, when wet, with either a glass or a plastic cover at an angle to reduce drips from condensation, see figure 3 below.
The frame should face north but if this is not possible, shade it with nylon shading material until the seeds have germinated. The shade lovers can remain in the frame until large enough to handle whilst you should move the remainder into more light on germination. When the first leaf or pair of leaves, the cotyledons appear, you may begin trans-planting or ‘pricking out’. It is easier to pot individually into 60 to 75mm (2.5 to 3 in) pots, but where space is limited, seed trays or similar containers can be used. When roots begin to fill the containers, plant the seedlings I into their permanent positions. An ideal re-potting mixture for seedlings contains 50% John Innes No. 1 potting compost, with 20% extra peat, and 30% extra grit.
Fig. 3 Sowing: (a) seeds of average size (b) large and feathery seeds (c) fine seeds. The frame should face north, if not, shade it with nylon shading until germination.
All are covered with a layer of shingle or pea gravel. The pots, plunged in coarse sand, are, when seeds have germinated, covered with glass lights at a shallow angle or plastic lights at an angle of 30° or more to reduce drips from condensation.
Division of Alpine Plants
Propagating plants by division is a simple method and it produces instant results which can be planted straight away. Herbaceous plants can be divided between autumn and spring. Begin by cutting down most of the stems and leaves to within about 2.5cm (1 in) of the soil surface. Insert two hand or border forks, back to back, down into the outer part of a lifted plant and push the forks apart. Do this as often as necessary until you have the number of plants you require. Always avoid the central crown area of any herbaceous plant, for it is woody and hard, whereas the outsides are young and fresh, and small plant-lets will grow more satisfactorily than large clumps – see figure 4.
Cuttings from Alpine Plants
Propagating plants by means of cuttings is particularly appropriate for hybrids, or ’cultivars’ (cultivated varieties) as they are known. These are plants which if grown from seed do not exactly reproduce the parent colour, flower or shape. Hybrids of variegated plants revert to their uniformly green form.
Cuttings should be taken from good healthy plants at times when rooting has its greatest chance of success. Wherever possible avoid taking cuttings when the plants are in full flower, because at this time most of the plant’s energy is going into making the and not the wood. As a general guide take cuttings shortly after flowering just as the new growth is becoming firm. Most alpines flower early and cuttings can be taken in June or July. With those plants that flower later, take cuttings of soft growth in the spring and early summer. Conifers and Aubrietas are exceptions; they should be taken in the autumn: September or October.
These guidelines apply to cuttings taken from the tops and sides of soft wooded plants. In the case of dwarf conifers, the cuttings must be taken from the side growths only, otherwise the resulting plants will tend to be larger, or, if the cuttings come from the bottom growths, smaller than the original.
It is always better to take small cuttings; larger ones take longer to root and are ultimately slower to grow. Approximately 10 to 30mm (1/2in to 1 1/4in) is long enough for most, although larger plants will need longer pieces.
The two most common methods of taking cuttings are by nodal cuts for soft growth and heel cuts for harder, wooded stems. To take a nodal cutting, slice straight across the stem below a leaf or pair of leaves, and remove the lower leaves with a sharp knife (see figure 5 (a)). Take a heel cutting by tearing a young growth from a strong stem with a sharp downward pull; neatly trim the resulting ’heel’ and remove the lower leaves (see figure 5 (b)).
Cuttings can be planted out into almost any kind of container, but it is easier to re-pot the rooted plant if it is tipped out of a plant pot. Insert all cuttings almost up to the leaves in a mixture of equal parts of coarse sand (not soft builders’ sand) and peat. Moistening the sand will make it easier to insert the woody cuttings, while an old ball point pen is ideal for planting softer ones. Keep the cuttings in a warm place if possible, but away from direct sunlight.
As with seeds, the containers can be plunged into coarse sand or grit, to maintain an even temperature and reduce the need for watering but unlike germinating seeds, it is better to keep cuttings under glass or a plastic cover to retain warmth and some humidity until they are rooted. It is a good idea to add a proprietary copper solution when you water the plants to help prevent ‘’.
Watch the cuttings daily. Remove any blackened or damped-off cuttings or yellowing leaves immediately. Pot the cuttings individually when they are rooted. To test for rooting pull gently on the cuttings; if they remain firm they are ready for potting. Pot into 60 to 75mm (2 1/2 to 3 inches) containers and leave under cover for about l0 days, then remove the cover and let them grow until they are ready to plant out. Use the same soil mixture as for re-potting seedlings.
Alpine Plants – Root Cuttings
Plants which produce thick fleshy roots can be propagated by making root cuttings. Dig out one or two roots from the soil in January to February and cut them into a series of pieces about 20mm (3/4 in) long. To ensure that you insert these cuttings the right way up, make a straight cut at the top and slice the bottom at an angle. Bury the entire cutting under the sand and keep the containers almost dry until growth appears on the surface.
Layering Alpine Plants
Layering is a simple method of reproduction, ideally suited to those plants such as Rhododendrons which produce woody stems at fairly low levels.
Choose one or more branches whose growth is reasonably flexible and scratch out the soil immediately below. Replace the original soil with sand, if the plant requires well drained conditions, or sand and leaf mould for woodland types, like Rhododendrons.
Pin the branch down into its new position with a peg of hazel wood or a piece of wire, and cover the stem with about 20mm (3/4 in) of soil. Gently bend the branch almost vertical, just past the peg and tie it to a bamboo cane, in that position. If the peg begins to rise, weight it down with a stone (see figure 6).
Ifis done in the spring, the new plant should have rooted by the following spring and can be cut from the parent plant and transplanted, in the autumn.
Fig. 4 Division: cut down stems and leaves to within 2.5cm of the soil surface. Push two small forks, back to back, into the crown of the plant and force the forks apart.
Fig. 5 Cuttings: (a) nodal: make a straight cut below a pair of leaves (b) heel: strip the cutting from wood of the previous year (c) root: cut tops horizontally and bases diagonally.
Fig. 6 Layering: use a peg to hold down the branch. Cover stem with about 20mm of soil.