Clumber Gardener: Take root cuttings now and reap the rewards next spring

Chris Margrave, head gardener at Clumber Park
Chris Margrave, head gardener at Clumber Park
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Propagating herbaceous plants from root cuttings is something even the keenest of gardeners is often reluctant to try, favouring instead increasing stock by stem cuttings or by dividing clumps of perennials during the dormant season.

Each method has its pros and cons.

Root cuttings can be taken between now and February whilst the plants are dormant.

Lots of plants can be produced from a single parent plant using this method and those which have foliage pests, such as stem and leaf nematodes are given a clean start.

Disadvantages are that roots develop underground, so you can’t see what’s happening as there are no developments above ground until shoots start to grow.

Also, variegated plants will revert to their plain green-leaved form.

Plants which naturally produce new shoots from their roots will respond to this method.

This includes phlox and verbascum and drumstick primula (Primula denticulata) and oriental poppy, neither of which respond to being propagated as stem cuttings.

The parent plants chosen to be propagated should be dug out of the ground with a garden fork, taking care not to damage the roots.

Use secateurs to cut off sections of root and re-plant the parent plant.

Wash the cut off roots in water to remove any soil.

There are two distinct methods, depending on how thick the roots are.

Thicker rooted plants, such as verbascum and oriental poppy, should be cut into lengths of about 7.5cm.

It is important to remember which way up the root was on the parent plant, as the top of the root cutting is cut horizontally, and the bottom at an angle of 45 degrees.

Cuttings are inserted vertically, about 2.5cm into a pot with a suitable cuttings compost such as equal parts peat substitute and sand.

The end with the angled cut is at the bottom, the horizontal cut end is just below the surface of the compost.

Roots will form at the end which was furthest away from the crown of the parent plant.

Cover the compost with a thin layer of horticultural grit.

This will discourage moss and algae growing on the surface.

Water the compost, label what’s in the pot and put it in a cold frame.

In the spring the cuttings will start to produce shoots.

These can be potted up individually into a suitable sized pot and grown on for planting out the following year.

Plants with thinner roots, such as Japanese anemones and phlox should be cut into longer sections of around 10cm.

These are laid horizontally on the cuttings compost, again about 2.5cm apart and covered with about one centimetre of compost, which is gently firmed, covered with grit and watered.

If you are propagating large numbers of these thinner root cuttings, a seed tray can be used rather than a pot.

Although usually associated with herbaceous perennials, some shrubs can also be propagated using root cuttings.

These include the tree poppy (Romneya coulteri), stag’s horn sumach (Rhus typhina) – although be careful when handling this, as some people are allergic to its sap, and the ornamental brambles.

With these shrubs, especially if they are large, it is better to dig carefully at the base of the plant to reveal suitable root material, rather than dig up the whole shrub.

December is now upon us and tools and gadgets such as secateurs, max-min thermometers and a stainless steel spade, and gardening books all make suitable Christmas gifts and can be tactfully suggested to family and loved ones.

You can now also order seeds from the new catalogues or online.

Look out for new varieties and have a go at growing one or two next year.

November has been very mild. Clumber had its first frost over the weekend November 21 and 22m blackening the dahlias in the Walled Kitchen Garden.

These can be cut back and, if your soil is free draining and they are growing in a sheltered site, have their crowns covered with straw to protect them from the frosts.

Alternatively, on heavier soils and colder localities, lift the tubers and store them over winter in a frost-free greenhouse or shed in a tray with old compost packed round the tubers.

Make sure all frost protection is in place and pots with outdoor plants are protected with bubble pack.

Outdoor taps and pipes should be insulated or turned off and drained.