Propagating plants by root cuttings
Propagating plants by root cuttings is one of the easiest ways to multiply plants and the cuttings almost look after themselves!
There are a couple of times in the year when root cuttings are most successful and November is one of those.
The other time is in early spring but I find that there is so many other gardening tasks then calling for my attention that late autumn is the best time for me.So why is this much neglected propagation method so easy?
Well roots lose little moisture when detached from the parent plant. Whereas the tops of plants, and especially parts that have leaves, are losing water from the minute your sharp knife cuts it from the plant that you want to multiply!
Now we do everything we can to slow this moisture loss down.
But until new roots grow and the cutting is able to replace any lost water through its new root system, it is going to be under some stress.
And stressed cuttings do not root well.
There is however an important catch and that is unfortunately not every plant can be propagated this way!
Nevertheless there are plenty of good plants to increase by this method. Whether you just want one to give to a friend or several to create a bolder display in your border, this can produce great results!
Plants that are successfully propagated by root cuttingsThere are many hardy perennial plants that are regularly propagated this way.
Some herbaceous but also some that are woody!
Often an indication of a plant that can be propagated from root cuttings is that it produces a new plant if you accidentally chop through a root!
The stag’s horn sumach [Rhus typhina] is a good example and in this case I suggest that you try propagating the cut leaf form ‘dissectum’ this way.
It is in any case a far more attractive and better behaved garden plant!
But it is primarily herbaceous perennials and particularly those that disappear underground for winter where there are most successes.
The Primrose Family
Many plants in the primrose family [Primula] can be propagated this way.
The drumstick primrose Primula denticulata is a prime example but there are others such as Primula rosea and many of the lovely candelabra types that flourish in damp and streamside plantings.
Other herbaceous perennials
Pulsatilla the pasque flower is another early bloomer to propagate this way.
Dicentra – that popular early spring bloomer – can be propagated this way too. It’s sometimes called Lady in the Bath or Dutchman’s Breeches because of the novel flower shape.
And talking of breeches, Acanthus or Bear’s Breeches is mostly propagated this way.
Sea holly [Eryngium], with its lovely steely blue flowers and prickly leaves, is another prime contender to be multiplied.
A new Eryngium called ‘Neptune’s Gold’ was launched at the 2014 Chelsea Flower Show. This is a very exciting addition to this beautiful group of plants.
They are so well suited to well drained and sunny places.
A word of caution seems appropriate at this stage. Some of the latest and most exciting new plants are subject to breeder’s rights. For these propagation for sale is expressly prohibited. You might care to read more on Neptune’s Gold and its introduction here.
Mullein [Verbascum] likes similar conditions to sea holly. Many can be raised from seed but the best varieties can only be perpetuated by asexual reproduction. Propagation by root cuttings is a prime example of asexual propagation.
So, you can be sure that the plant that grows from the root cutting that you take will produce exactly the same colour bloom and plant shape as its parent.
Poppies and more
This is especially so with Oriental poppies [Papaver orientalis hybrids]. Grown from seed most will bloom various shades of red. But propagated by root cuttings the flower colour will be exactly the same as ‘mum’! These produce large cuttings as thick as a pencil and are easy to handle.Some have much finer roots but are well worth the fiddle.
I’m thinking in particular of the beautiful scented and showy border phlox [Phlox paniculata].
Some other plants that are worth trying are Japanese anemone and Campanula.
More woody plants that can be propagated by root cuttings include Catalpa, Clerodendron, lilac, Aralia and Chaenomeles. Climbing plants such as passion flowers, Solanum and Campsis will root this way.
Beware that many lilac are grafted onto dull flowering seedling rootstocks.
Other benefits of Root Cuttings
Well to take root cuttings you first need to get at a plant’s roots!
But before you get carried away with that spade just give a thought to how healthy the plant is. Were the leaves mottled? Was the flower the right shape and colour? Did the stems grow naturally?
All these can be indications of whether your plant is healthy or not.
Old plants sometimes become infected by virus diseases. Any plants propagated from them will also be adversely affected by the virus.Sometimes root cuttings can reduce the chance of a problem.
Take for instance border phlox. They are prone to leaf and stem eelworm infestation and there is no real cure for this.
But these eelworms rarely venture down into the root system. So that plants arising from root cuttings will often be free of this major pest!
How to take Root Cuttings
Okay, you’ve checked that the plant is healthy and that it is a type of plant that will propagate with root cuttings and so you are ready to start.
Dig all the plant out of the ground but with woody plants it is better to just expose a few good roots. Wash the soil away so that you can see what you are doing.
Polarity is important
Use a sharp knife to cut off good healthy roots. Remember which end is the root tip and which was attached to the top of the plant. This is terrible important for cuttings that are thick! You are going to need to insert them into the compost so that the root tip end is at the bottom.
But with plants with thin roots, such as Primula and Phlox, it is far less important as these can be laid flat on their sides in rows and then covered with compost.
The roots will emerge from one end and the shoots from the other!
There are no real hard and fast rules but root cuttings should be about 5-7 cms long. The thick ones should be pushed into compost so that the top is flush with the compost surface.
A useful tip is to always cut the top of the root at a right angle. Cut the bottom, which is nearest to the shoot tip, at 45 degrees.
At a glance you can then see which the top is and the slanted cut helps insertion of the cutting.
What to put your cuttings in
Use pots or trays filled with well-draining compost mix. Add up to 50% by volume of sharp sand or horticultural grit. This will ensure that it is free draining.
Water well and periodically ensure that the compost remains moist.
You won’t need plastic or glass covering.
If you have a heated surface on which you can stand these pots and trays that will encourage rooting but the tops should be kept cool and frost free.
Light is not needed until the first shoots emerge.
In spring shoots will appear but be patient as roots take longer to get going.
It may be mid-summer before you have little rooted cuttings to pot up and grow on.
Find out more
Have you had success propagating plants by root cuttings? If so, which varieties have worked for you?
Enjoyed learning about root cuttings? You might then be interested to read about hardwood cuttings too.
How about softwood cuttings in late summer? Read more here.