Layering
Some plants will naturally propagate themselves by layering. The runners which grow out of strawberry plants, for example, will often root themselves at points where the runner touches the soil. This natural tendency can be used to propagate plants in a more controlled way. Once the stem is rooted it can be severed from the parent plant, so the new plant grows on separately. Layering is a very easy way to create new plants because the parent continues to provide nourishment, until severed, so it requires less care and attention than, for example, stem cuttings.
There are several different ways of layering plants:
Simple layering
This is a quick and easy way of propagating a few new plants from an existing shrub, climber or herbaceous perennial (which has a propensity to grow aventitious roots), which is generally done in autumn (although herbs are layered from ripe shoots in summer). Select a pliable stem which is no more than 2 years old and growing close to the ground. Prepare the ground where you are going to layer the plant by removing all weeds and debris, digging it over lightly and adding some free draining organic matter (such as garden compost) ensuring it is mixed thoroughly with the soil.
When you are ready to layer the stem, trim any leaves or side stems from the section you are going to layer, to at least 30cm below the tip (retaining a few leaves at the tip if you wish). Carefully wound the stem where it will touch the ground; ideally this should be where the 1 year old growth meets older growth, but if in doubt do it about 15cm from the tip. The stem can be wounded by making a slanting cut about 2.5cm long on the underside, removing 2.5cm of bark from the underside, or twisting the stem tightly to damage the outer layers. If you have cut the stem, you may wish to dust it/dip it in a hormone rooting compound to encourage rooting.
Pin the stem, wound side down, onto the soil to ensure that it makes good contact with the soil surface. If you don’t have appropriate pins for doing this, you can use a wide hair pin or the hook of a wire coat hanger. Cover the stem, where it touches the soil, with about 8cm of soil to form a small mound, and firm gently. Put a stake or cane in the soil next to the layered area and tie the tip of the stem to it, to encourage upwards growth. If the stem you are layering isn’t growing very horizontally, you can dig a small trench to layer the stem in, then covering it up, to ensure it remains under the soil.
As the stem takes root, ensure that you check that the ties on the stake aren’t too tight, and loosen them as approprate. Water regularly in dry periods and keep the area weed free. If the plant is sensitive to cold weather, cover the layering area with fleece of straw in colder periods.
When the stem has rooted (this will generally take about a year), cut the stem joining the new plant to the parent and dig it up, taking care not to damage the delicate new root system. Re-plant or pot up as required.
Tip layering
Tip layering is very similar to simple layering, only the point of root growth is at the stem tip, rather than in the middle of the stem. Rubus species, for example, tip layer readily. Prepare the soil in the same way as simple layering. Choosing a vigorous, healthy stem, bury the tip into a 10-15cm hole. The stem can be pinned down to keep it in the hole. Back fill the hole and firm down, ensuring you do not damage the stem.
Keep the soil moist and weed free. When the tip has rooted (this may take as little as a few weeks) cut it from the parent plant, leaving about 25cm of the old stem. Move the new plant to its new location or pot it up.
Serpentine layering
Where the plant has lengthy stems (eg climbers) serpentine layering can be used. The basic method is the same as for simple layering, but instead of wounding and pinning down the stem at only one point, you select several points along the stem to do this.
Mound layering
The mound layering propagation technique is often used for perennials which are past their best, such as lavenders,violas and rosemary. A mixture of one third soil, one third peat or coir and one third sand should be piled over the plant to a depth of around 10cm so it covers the bottom half of the stems. Keep the mound maintained (particularly check it after hard rain) and top it up as necessary. After between 6 and 12 weeks the stems should have started to form roots. They can then be detached from the main plant (cut them just below the lowest new root) and potted on/planted out. The parent plant is then disposed of.
Stooling
Stooling works on the same principle as mound layering, whereby the parent plant’s stems are covered with soil in situ to encourage rooting. Stooling is often used with shrubs or trees to provide rootstocks for grafting.
Select a healthy, 1 to 2 year old plant to use as the parent which has plenty of stems shooting up from ground level. In late winter or early spring cut the stems back to about 8cm in length to encourage new shoots to grow (technically it is this part of the process which is called stooling). In spring, when the new shoots are about 15cm long, pile earth up against the base of the shrub to about 10cm. Add another layer of soil in late spring/early summer and another in late summer; each layer added should encourage further root growth from the stems.
In late autumn, careful ease the soil mound away from the plant using a rake or fork. Use your hands or a hand fork to carefully tease out the new roots so you can see clearly where the new roots are growing from the earthed up stems. Taking care not to damage the roots, cut the rooted stems from the parent plant, just above the neck of the original plant. Plant out or pot up the stems to grow them on and re-cover the roots of the original plant (which should re-grow).
Dropping
Dropping works in the same way as mound layering and stooling, but instead of piling soil up around the plant, the plant is ‘dropped’ into a hole. This is commonly used in the propagation of heathers.
The plant should be dug up and a new hole created which is two-thirds the depth of the entire plant (ie from the base of the rootball to the tip of the stems). The plant should be placed in the hole and the soil carefully back filled to cover the roots (ensuring good contact with the soil). Continue to fill the hole to soil level (ie to cover part of the top growth) with half grit and half peat or coir.
Keep the plant watered during dry periods. Once rooted (which should take about 6 months) lift the whole plant carefully. Brush off the soil and cut the rooted stems from the parent plant. Plant up or pot on the stems in a sheltered location to grow on.
French layering
This is a very reliable layering method for shrubs. Cut back the plant you wish to layer to about 5cm in spring, which will encourage new shoots to grow. Early in the following spring, trim the growing tips from the stems you want to layer (to encourage side growth) and pin the stems down on the soil surface. You can do this with multiple stems from around the outside of the plant, so they radiate out from the parent plant in all directions. Side shoots should grow upwards from the stems. When they are around 8cm tall cover them with soil so that only their tips are protruding. Repeat this again in the summer to a depth of 15cm. Ensure that you keep both the parent plant and layered stems watered and weed free.
In the autumn, carefully remove the mounded soil to reveal the new roots and cut each rooted stem free from each other and from the parent plant. Plant or pot up each stem to grow on.
