I cleared Border 6 last weekend. In doing so I removed the giant solidago that was bullying everything else in the bed. This revealed a sickly looking eryngium. I wondered where that had got to! It was great last year, but has not done a thing this year, I thought it had died. I dug it up with the intention of discarding it, but noticed that it had plenty of nice fat roots. Eryngium, or sea holly, is a plant that can be propagated by root cuttings. The advice is to take these in mid to late Autumn, so I’m a bit early really.
The advice is also to remove no more than one third of the roots at a time, to give the parent plant a chance to recover when replanted. In my case I’ve taken all the roots as I thought the parent plant was a goner anyway. I cut the roots close as close to the crown as I could get. Fatter is better, pencil thickness is about right.
I removed the finer rootlets and trimmed off the flimsier end of the root, leaving me with fattish lengths of root. It’s important to keep track of which way up the root is – the new growth comes from the top of the root, the end that was closest to the crown. It’s common to read that a flat cut on the top and a slanted cut on the bottom is a way to identify which way up the root is but I’ve found it just as easy to carefully lay them out in a line on the bench, the top at the top, bottom at the bottom. I should have washed the roots, I forgot.
The longer fat roots were cut into two, so I had 10 or so bits of root to play with.
I used a gritty compost mix, roughly two parts grit to one part vermiculite, in a clean 9cm square pot. Setting the cuttings up is a simple matter of poking a hole in the compost, easier if the compost is damp, and pushing the root cutting in. Again, make sure the top of the cutting, the end that was closest to the crown, is at the top. It should be just under the surface of the compost. The new growth will emerge from the very top of the cutting.
The root portion has the reserves necessary to produce new growth quite quickly, but beware. This new growth is not a sign that new roots have developed. Resist the temptation to muck about with them, leave alone until you see new roots emerging from the bottom of the pot, and plenty of them. This might not be till the spring. The root cuttings need to be kept moist but will rot off if waterlogged, and any new growth will die if left to dry out entirely. Avoid overwatering, basically. In theory a cold-frame is sufficient protection, I’m going to leave mine on a unheated bench in the greenhouse for now, see what happens. In the spring I should be able to pot them on and feed till ready to harden off and plant out. I hope.
I decided in the end to pot up the parent plant, a bit of fresh compost and luxury accommodation in the greenhouse may encourage a resurrection next year. I’ve also read that a good way to get lots of roots to propagate from is to have a potted parent plant growing away on top of a bed of sand. The roots come through the pot and into the sand, at the end of the growing season the pot can be lifted and the roots trimmed back to the bottom of the pot, with the trimmings providing the cuttings material. This avoids the problem of disturbing the parent plant to get at the roots, some of which can object and sulk. I might try that next year.
I’ll be back soon with more propagation news.
Update 22-01-18. These cuttings have worked really well! I have done nothing since taking the cuttings, the pot has been minding its own business on the bench in a cool greenhouse. The larger pot on the left is the parent plant, which seems to be staging a recovery, somewhat to my surprise. I will leave the cuttings in their pot (right) until the spring when I shall pot them up. Very pleased with these…!