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More plants layer by layer
7:00am Saturday 12th May 2012 in Homes & Gardens
Tips on how to increase stocks of plants such as rhododendrons, camellias and magnolias - plus, find out what else needs doing in the garden this week.
By Hannah Stephenson.
It's cuttings season, when gardeners nationwide take cuttings from their plants to increase stocks of their favourites, but not all plants root well from cuttings.
Some plants, including acer, forsythia, daphne, viburnum, rhododendron, azalea and camellia, may do better through layering, a technique in which layers of healthy stems remain attached to the parent until roots have formed.
Layers occur naturally in the garden when low-growing plants are heavily mulched, thus partially burying some of the branches.
Plants including ivy, campsis and Hydrangea anomala subsp. petiolaris naturally self-layer, with shoots touching the ground rooting and forming new plants, but in most cases the gardener has to provide some input into layering chosen species successfully.
Spring is the best time for layering, although it can be done at any time of year apart from winter.
Choose a flexible young shoot of your chosen plant which can be bent down to ground level, preparing the soil where it is going to touch by digging in well-rotted organic matter, such as compost mixed with sharp sand. Strip the leaves from the area of stem to be layered.
Make a long, sloping cut towards the shoot tip, cutting only about a third of the way through the stem at a suitable point in the underside of the branch, then wedge the cut open with a matchstick and dust it with rooting hormone.
Make a shallow depression in the soil just below the shoot, then bury that section of the stem into the prepared soil 5-7.5cm (2-3in) deep and peg it firmly in place with two strong wire hoops, one each side of the cut, then secure the growing tip to an upright cane and cover it with compost.
As the layering is done at the base of the shrub, the greatest danger to rooting layers is lack of water, so give it a thorough watering and, if necessary, work some water-retaining material into the soil.
Leave it for at least a year until new strong growth is visible and the plant resists when tugged, which shows that it is well rooted.
Most layers should have rooted by the following autumn, when they can be severed from the parent plant and grown on in pots or a nursery bed until large enough to plant in their final positions.
Stocks of climbers, such as honeysuckles and clematis, can be increased by serpentine layering, which is similar to simple layering, but multiple layers are made from one stem. It's ideal for using with climbers with long, supple stems.
Lay the trailing shoot along the ground, stripping the leaves and sideshoots from every second or third leaf cluster, then wound the stem close to the points where the leaves have been stripped and apply rooting hormone before pegging these sections down in shallow trenches in well-prepared soil. Thin-stemmed climbers need not be wounded.
Leave the intermediate leaf clusters above the ground so that the stem snakes in and out of the ground. In time, the pegged down sections should root and produce shoots. When growing strongly the new plants can be severed and grown on independently. This method can also be used for houseplants which are hard to root, such as ficus.
A third method is air layering, which is ideal for plants which often lack low-growing shoots suitable for conventional layering, such as magnolia, hazel, cotinus and flowering cornus species.
Instead of taking the stem down to the ground, choose a healthy upright stem and trim off the side shoots and leaves from a 30cm (1ft) section, making an upward-slanting cut below the leaf joint, but not cutting more than half way through the stem.
Brush the wound with rooting hormone compound and wedge a matchstick into the cut, then tape a sleeve of polythene around the bottom of the cut, plugging the sleeve with sphagnum moss for the roots to grow into and then seal the top. Keep the moss moist.
Leave the wrapping in place for up to a year, opening and checking it occasionally for signs of rooting. When strong new roots are visible through the moss, remove the plastic sleeve and cut through the stem just below the rooted section, which can then be potted up into compost, but don't remove the moss from the roots. Water, label and grow on until large enough to plant outside.
In little more than a year, you could have doubled the collection of your favourite plants.
Best of the bunch - Lily-of-the-valley (Convallaria majalis) If you want spring scent in a natural setting, colonise these sweetly scented, white-flowered beauties in a moist, shaded spot, ideally a woodland garden, or under deciduous shrubs so that their small bell-shaped flowers stand out against a background of newly opening spring leaves.
Within a few years, one or two small plants will have spread to a sizeable mass, growing to around 23cm (9in) tall, their fragrant flowers appearing between dark green leaves.
They make ideal ground-cover plants for shady, damp situations, spreading quickly by means of creeping roots.
Good varieties include 'Albostriata', with its gold-striped leaves and 'Fortin's Giant', which is slightly taller, growing to around 30cm (1ft).
Be warned, though, don't put lily-of-the-valley into tightly contained beds as they are vigorous spreaders and once you have them, it will be difficult to dig them all out.
Lift some of the rhizomes and pot them in autumn for a display of fragrant flowers indoors.
Good enough to eat - Planting globe artichokes These easy-to-grow veg are grown for their tasty flowerbuds before the flowers open, but are also a valuable architectural addition to the vegetable garden, growing up to 1.5m (5ft) tall with silvery leaves rather like a thistle, although you shouldn't need to support them.
Sow them on a warm windowsill in February, pricking out the strongest seedlings into individual pots and gradually harden them off. Plant out young plants in mid spring, spacing them 90cm (3ft) apart with a little more space between rows.
Globe artichokes grow well in a warm, sheltered, sunny spot in well drained, rich soil and will need a year to establish before you can reap a harvest, but cut off the buds and don't allow them to flower in the first year. That way, they'll store up their energy for a good crop the following year.
Water them well in summer, especially during dry spells, and feed them with a slow-release fertiliser each spring.
When the plants die down in autumn they can be cut right back. 'Green Globe' is the variety most commonly available for growing from seed, although you can also buy small plants from nurseries and garden centres.
Three ways to... Make your veg plot pretty 1. Grow sweet peas and climbing beans up wigwams in the centre of a uniform plot to add height and colour.
2. Use ornamental herbs such as sage and thyme at the front of the veg border as a colourful but neat edging, or lavender and rosemary which can be clipped to achieve a more formal look to the border.
3. Plant a mixture of vegetables and flowers to give a cottage garden effect. Flowers which will complement some vegetables include cosmos, pot marigolds, achillea and zinnias.
What to do this week :: Sow fast-maturing and late-flowering annuals, herbs and vegetables including parsnips, early carrots and runner beans.
:: Harden off summer bedding, checking the forecast and covering the plants with horticultural fleece if frost is forecast.
:: Thin out hardy annuals, vegetables and other seedlings sown outdoors.
:: Take basal cuttings of border plants such as lupins and delphiniums before they develop pithy stems which won't be suitable for cuttings.
:: Prune spring-flowering clematis after flowering.
:: Finish planting permanent containers so plants have the summer to establish themselves.
:: Prune winter-flowering heathers.
:: Earth up early and maincrop potatoes.
:: Cut lawns with naturalised bulbs growing in them, keeping the mower blades high.
:: Protect young plants from slugs.
:: Replenish water plants with aquatic fertiliser.
:: Divide and cut back spring-flowering perennials.
:: Trim box and other formal hedging lightly.