Its easy to think that taking cuttings is a thing you do in the summer or maybe in the autumn, when the plant is in full growth. For a particular type of cutting though, you want the plant to be dormant and that is for root cuttings. The best time to do this type of propagation is therefore in the winter months from December to March. Root cuttings aren’t difficult and if you master the technique this is a great way to get plants for free and to be sure that the plants you grow will be exactly like the parent plant.
There is a surprisingly long list of perennial plants that can be propagated in this way, including: Anchusa, Acanthus, Brunnera, Dicentra (Bleeding Heart), Crambe maritima, Echinops (Globe Thistle), Eryngium (Sea Holly), Campanula, Campsis (Trumpet Vine), Chaemomeles (Japanese Quince), Clerodendron, Japanese Anemones, Pulsatilla (Pasque Flower), Phlox, Primula denticulata (Drumstick Primula), Passion flower, Papavar orientales (Oriental Poppy) and some of the hardy Geraniums such as Geranium praetense and sanguineum. You can even take root cuttings from some fruit such as Raspberries, Blackberries and Figs.
Root cuttings are simple, but there are a few things to think about; although you want to do this when the plant is dormant you need to avoid periods when the ground and plant might be frozen. You also need to be careful how much of the root you cut off if you want the original plant to continue to thrive, as a general rule never take more than a third of the root system. Some of these plants which have a major tap root will not respond well to being dug out of the ground so for plants like the Sea Holly Acanthus or the Pasque Flower for example, you need to excavate soil at the side of the main root ball and snip off roots from the side without causing major disturbance to the existing plant.
For plants with a vigorous network of roots that form a definite root ball you can dig up the whole plant, wash off the soil so you can see what you are doing then cut off 4 – 5 inch pieces of the thicker roots close to the crown of the plant before replanting the donor plant back into the soil.
Once you have your root cuttings, like all cuttings, you need to prepare and pot them up straight away for the best chance of success. To prepare your root cuttings firstly make sure you know which way up they need to be planted in the pot. To do this, as you cut them off the plant, make a straight cut across the top of the root (i.e. the part nearest the centre of the plant) and a diagonal cut across the other end of the root section. Take off any small side roots and any very thin ends with a sharp knife. For plants with thick fleshy roots, like poppies put 4 or 5 cuttings about 2″ apart around the edge of a large 2 litre pot filled with a 50:50 mix of compost and fine grit/sand or perlite. Push the root cuttings into the pot so that they are just below the surface then cover with grit or vermiculite. Water well when you plant them and then sparingly until the spring, overwatering will lead to them rotting. Put the pots in a cold frame or sheltered spot where they won’t get frosted or waterlogged. For plants with thinner roots where you would struggle to push them into a pot vertically, lay slightly shorter root sections 2″ – 3 ” long horizontally onto the surface of a seed tray cover lightly with the compost/grit or perlite mix or with vermiculite and then cover with a sheet of glass or put the tray into a plastic bag into a plastic bag and leave in a cold frame or unheated greenhouse.