Recently, a friend and I were singing the praises of the 'Mesa' range of small Salvia, some of which have done brilliantly in a local park planting that we are involved with, proving to be incredibly robust and flowering well for many months. However, we bemoaned how hard they seem to be to propagate. Their very thin stems seem to make cuttings very difficult to strike. My friend suggested that 'layering' might be the answer and my interest was piqued in this ancient form of propagation. This week I have put it into practice with my own 'Mesa' plants to see how it goes.
Layering often happens naturally when a low branch of a shrub or shrubby perennial lies on or somehow touches the ground (perhaps by being partially broken) and becomes covered with soil, old leaves or other organic matter. In time, due to totipotency - the genetic potential of a plant cell to produce the entire plant - the point at which the branch touches the ground forms roots and becomes an independent specimen. Plants that I have noticed in my garden that have a tendency to do this on their own include shrubby Plectranthus, many Salvia, Iresine, Justicia brandegeeana, Odontonema tubaeform, Streptosolen jamesonii and Viburnum tinus. Many groundcovering plants layer themselves as they spread; examples include Verbena hybrids, Lamium maculatum, Plectranthus ciliatus, Plectranthus 'Nicoletta' - and indeed most other Plectranthus groundcovers. Other plants that can be induced to layer include Daphne odora, lavender, Cistus, rosemary, Buxus, Elaeagnus species and cultivars, Magnolia, Trachelospermum jasminoides and azaleas.
The basic technique is to improve the soil a bit in the place where you plan to grow your layered plant, by digging it over and adding some compost. Then remove a sliver of the bark near a node on the underside of a flexible stem that is growing in such a way that it can be anchored to the soil. Bend it over without breaking it, pin it down firmly, then cover the spot with some soil or compost, and water with some diluted seaweed extract. Probably the best stems to use are young, whippy stems but I am trying at the moment with more mature ones, which is all I have! Remove any foliage from the stem that will be buried by the soil. I used metal irrigation pins to peg the stems down, but a tent peg, a bent piece of a wire coat hanger, or a sturdy forked twig can suffice. Keep the area around the layer reasonably moist. All that needs to be done then is to wait patiently for the layer to produce roots. This may take some time! Once the roots have formed, cut the layer free from its parent but leave it in position for a while until it appears to be growing strongly, then dig it up sometime later and replant where you want it to grow.
Shrubs that have very upright branches are hard to layer with this method, but luckily there is an alternative technique called 'air layering' that can be used. Again, young, strong stems are ideal to use but it can be tried on older ones too. A sliver of bark is again removed from one side of the stem, then moist, water-holding material such as sphagnum moss or coco-peat is wrapped around a section of the stem, including a node, then enclosed in a layer of opaque, waterproof plastic sheeting, which is securely sealed with tape, to make a strange type of package. This keeps rain out yet retains the moisture in the sphagnum moss around the stem whilst roots form. Once roots have formed, the branch is cut off and potted up individually, to be grown on for a while before being planted out in the garden. Suitable subjects include Camellia, Magnolia, Pieris and Rhododendron. This method can also be used with indoor plants, especially those that develop little roots at nodes anyway, such as various Monstera, Philodendron and Syngonium species and cultivars.
I'd love to hear of your experiences with this method of propagation!
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