Advice
RHS Help & Advice
Root cuttings
Images: Tim Sandall
Some herbaceous plants, such as Acanthus, Anemone hupehensis, A. x hybrida, Echinops, Papaver orientale, Phlox, Primula denticulata and Verbascum, can be propagated from root cuttings at this time of year
Choose vigorous clumps to propagate. Good roots can be obtained from older plants by lifting them in autumn and trimming top and root growth to within 5–10cm (2-4in) of the crown. Replant in prepared soil to encourage young, vigorous roots for propagating the following autumn. Root cuttings cannot be used to propagate variegated plants as the new plants will have plain leaves.
Lift the plant when dormant (here Papaver), which is usually in winter, and wash the roots. Select young, vigorous pencil thick roots and cut them off close to the crown with a sharp knife or secateurs. Remove no more than one-third of the root system, and replant them as soon as possible.
Cut each root into 5-10cm (2-4in) lengths making a horizontal
cut at the upper end and an angled cut at the lower end. Insert them into pots or trays of compost so that the top
of the root is just below the surface of the compost and top
dress with grit. For the compost use a mix of equal parts
peat substitute and gritty sand. Water the compost lightly
and place the pots or trays in a cold frame. Pot up individually when the cuttings show signs of growth
and are well rooted.
Grow plants on and plant out the following year. Some genera such as Eryngium and Pulsatilla have long taproots and resent root disturbance.
Carefully dig down the side of these plants to access a few
roots. Alternatively, in spring, place containerised plants
on a 15cm (6in) layer of sand in a box and sever the roots
produced in the sand in autumn for use as cuttings.
Many perennials, such as Japanese anemones, Campanula and Phlox, have thinner roots. Root cuttings should contain enough food reserves (carbohydrates)
to ensure survival and regeneration; thin-rooted species therefore
require longer root sections of 7.5-12.5cm (3-5in). Lay these horizontally, 2.5cm (1in) apart, cover with 1cm (1/2in) of compost and topdress with grit.