Conifers can be pretty! Flowers like these help to relieve otherwise ratehr monotonous foliage. Picture by Anne Burgess
Conifers can be pretty! Flowers like these help to relieve otherwise rather monotonous foliage. Picture by Anne Burgess

An interesting question about propagating from hardwood cuttings, this week, from Gary Oakeshott of Dorset:

‘Some conifer cuttings I took during the summer have [produced a hard knobbly base but not roots. what has caused this and will affect rooting?’

Hmm.. Gary, this knobbly surface is called callus and usually develops around a wound when favourable conditions for rooting are provided. It seems to be essential in the process of forming roots. The acidity of the soil can affect the production of callus: too much lime and the callus may be hard and prevent roots from breaking through.

I suspect the cause of your problem might be that you’re checking your conifer cuttings for root growth too often? A case of ‘digging up the plant to see if it’s growing’!! Each time you lift the cutting, another tiny wound may have been made and this will have had to callus over before rooting can occur. I suggest that you remove the hard callus with a clean, sharp knife and replant your cuttings- but this time be patient and leave them alone fora  good 2-3 months! Here’s a simple video of the conifer propagation process- useful if you want to extend a hedge with your own cuttings, for example.

The process of wounding cuttings to encourage rooting is an interesting one. You might think it opens up the risk of letting in disease, and whilst this is a possibility, the wounding of the base of woody cuttings seems to be beneficial, especially with those species that are difficult to root, such as Rhododendrons. the wound appears to stimulate root formation, and the cut area allows the roots to emerge from the stem more readily. For the greatest benefit, the cuttings should be treated with a hormone rooting compound after wounding prior to sinking them into compost.

Further information:

Taking hardwood cuttings- RHS advice

Old School Gardener