There are a number of methods of increasing your stock of shrubs. The most common way is from cuttings, and there are basically three types: softwood, heel and hardwood.
Softwood cuttings These are taken from the tips of the shoots, and should be from 2.5 — 15cm (1 – 6in) in length, depending on the plant. Trim each cutting to leave a straight, clean cut below a leaf joint, and take off leaves from the bottom half. Dip the base of the cutting in hormone rooting powder and tap it lightly to remove any surplus. This method is also used for basal cuttings (these are shoots coming from the base of the plant, and are gently pulled away).
Heel cuttings This is the most often used method of increasing shrubs. They are taken from semi-ripe material, I.e. green at the top and woody where it joins the main stem. The method of taking these is to gently pull the chosen cutting material down. It will come away with a small ‘heel’ of outer bark attached. Trim the cutting, leaving some of the heel, and dip it in hormone powder as before.
In both cases it is important to prepare the compost well. It should be of an equal mix of sharp sand and peat. Fill a pot with the compost, making a hole for each cutting with a small dibber. Insert each one, ensuring no air spaces are left (firming the cutting in place, with your fingers or a pencil, will ensure this). Water gently and place them in a closed garden frame. Shade from hot sunshine and ventilate well during the day. Cover the frame if the weather turns frosty. When well rooted, the cuttings can be potted individually to grow on. Alternatively, plant them out into a nursery bed. They are ready to go into their permanent position in the autumn or following spring.
Hardwood cuttings This method is used on a number of shrubs. It is a longer process and normally takes a year or more before the young stock is ready for planting out. Cuttings from well-ripened shoots of the current year’s growth are taken in late autumn. They should be 20-30cm (9-12in) long when trimmed. The top should be prepared with a sloping cut immediately above a bud. The base should have a straight cut immediately below a bud.
Dip the base in hormone rooting powder. Select a well-drained, lightly shaded part of the garden and with a spade, take out a small trench with one edge vertical. The bottom of the trench should have a 2.5cm (1 in) layer of equal parts course sand/peat mix, to provide a good medium for the roots to grow into. Lay the cuttings around 15cm (6in) apart, against the straight side, and gradually fill and firm theas you go. When finished, a third of the cutting should be above soil level.
Heavy winter frost can loosen the soil, so you may need to firm them again. It is essential to keep them watered in dry weather. In around 12 months the cuttings should have rooted sufficiently to plant them into their permanent positions. Hardwood cuttings can also be inserted into a suitably prepared garden frame.
Many shrubs can be increased by. Select a young healthy shoot from the plant, and it should be flexible as well, as it needs to be bent over and down to the soil level. With a trowel, take out a small piece of soil where you wish it to root. Place a small amount of sharp sand and peat, in equal amount, into the base of this hole.
Then, make a 2.5cm (1 in) long sloping cut on the bottom side of the stem, but take care not to cut through completely and sever it. A matchstick should be placed in the cut to keep it open. Bend the stem down so that the cut area is pushed into the compost mix, and then peg it in place. Cover the area with more of the rooting mixture. Tie the end of the cutting that is above ground level to a small support, to stop it from moving in the wind, or springing back into its normal position. Rooting can take anything from nine months to two years, depending on the type of plant.
Some shrubs can be increased by division. This should be done in early winter when soil conditions are suitable. Look out for suckers; these are shoots arising from below the soil surface and from around the base of the plant. Remove these by cutting or pulling from the parent plant, and replant them immediately. Plant them into a similar rooting mixture as described above.
Only a few subjects can be raised successfully from seed. Many have problems with germination and can take some time. It is worth considering, however, particularly with forms of Cistus and. Seed sowing is usually carried out in the spring. Fill a pot with a good loam-based seed compost, firm gently and water, leave to drain. Sow the seed thinly Space the seed out by hand if they are large enough to handle. Cover larger seeds with a thin layer of compost; fine seed should be left uncovered.
Place a polythene bag over the top of the pot, and hold in place with an elastic band. Put the pot into a garden frame and shade it from strong sunlight. When the seedlings are large enough, prick them out individually into 7cm (3in) pots. Repot them into larger pots as required, until they are ready to plant out in the autumn or following spring.