Many plants can produce stems (or shoots) from buds on their roots; by taking root cuttings, gardeners can propagate their favourite plants with little effort and a lot less time than by growing them from seed. The new specimens will be genetically identical to the parent plant, and cuttings of herbaceous perennials often flower during their first year of growth.
The trick to propagating from root cuttings is to take the cuttings when the parent plant is dormant: either in late autumn or first thing in spring. Woody plant material that is still young enough to handle easily is also well suited to this propagation technique.
How to do it:
1. Using a sharp spade or garden fork, lift the parent plant out of the soil (cut back excessive top growth by half for easier handling). Wash the soil from the root ball with a hose to expose the individual roots.
2. With a sharp knife, cut off the selected root pieces as close to the crown as possible (don’t take all the roots of the parent, though; your should leave up to half intact). As you remove each one, make a flat cut, at right angles to the root, across the top (shown at top right).
Next, trim off the other end (the bottom) with a sloping cut so the length is between five and eight centimetres (shown middle right). Remove any fibrous lateral roots on the cutting. Note: a single root piece can yield several cuttings depending on its size. Just make sure you trim each piece so the top is flat and the bottom is sloped .
3. Fill 12- to 15-centimetre-deep pots with moistened seed-starting or houseplant soilless mix to three centimetres below the rim. Make several holes using a pencil or knitting needle three to four centimetres apart, and insert cuttings vertically, making sure they are right-side up; the top of each cutting should be level with the soil surface (shown bottom right). Firm the soil back around them and cover with one centimetre of horticultural sand or fine gravel (e.g., rinsed aquarium gravel) to provide good aeration for the buds that will develop at the top of the cuttings.
4. Return the parent plant to its original hole, if desired; replacement roots will grow once it breaks dormancy.