Propagating Sea Kale - from Thongs and Seed

Someone on Twitter helpfully tweeted a reminder that this is the time of year to dig up plants to take root cuttings. I immediately thought of my sea kale as it is one of those plants which are easier and quicker to propagate from cuttings than seed.

Sea kale in flower
Sea kale in flower

Last year I decided to set out half a bed of sea kale plants on the allotment (see this post from last May) which we will hopefully harvest for shoots and leaves for several years to come. My original sea kale plant is still growing beside the pond in an area which I'm planning to make into a bog garden. An ideal candidate for sacrificing for use as root cuttings! I got stuck in and did my best to dig up as much of the root system as I could.

Excavating sea kale roots
Excavating the sea kale root

Excavated sea kale root
The result!

It was a somewhat sorry looking plant. I've had it up once before to harvest for root cuttings (which probably accounts for the truncated main root) and it's also been in a weedy corner for a year. You can't make them out in the photos above but there are several pink buds topping some portions of rather corky white stem at the top of the plant. The main root descends below the stem portions and long lateral roots grow from it (in this case they all head off under the fence into the neighbours plot for an unknown distance!) I've read that in the wild these lateral roots can be up to two metres long. (Wild plants can get very big - individual plants of up to five metres diameter have been recorded growing by the Baltic Sea in Germany).

The main root had some rot. According to this detailed study of the plant in the Journal of Ecology, this is very common in wild and cultivated plants as a result of poor soil and water-logging. The authors didn't consider it to impair the plants' vigour - which is just as well; the clay soil I'm growing my plants in doesn't get ravaged by the tides but it is considerably less well drained than the shingly or sandy banks of sea kale's native habitat. (Nevertheless, having read the study, I did take the precaution of clearing any dead vegetation from around the crowns of my plants.)

I've propagated sea kale successfully from short bits of root before but this time I followed the 'proper' method of cutting 15cm 'thongs' from the roots. You make a straight cut at the end closest to the plant and a slanting cut at the farther end so that you don't forget which end is which. Then the cuttings are tied into bundles and stored upright in slightly damp sand - with their tops just below the surface - in a cool place, for planting the following March.

Bundle of thongs and root for forcing
Bundle of thongs, remaining root for forcing and sea kale root nibbles!

Stored sea kale thongs
Stored sea kale thongs

Well if it's best to plant them in March, why not lift and cut them just before this? I think the reason for this is that traditionally you take cuttings at the same time as you lift plants for indoor forcing, i.e. after the first frosts in autumn. They also make a bit of growth prior to planting (the buds should be just breaking) and grow away quickly in the spring. The RHS advises that you rub out all but the strongest bud at the top of each cutting and plant the cuttings 38cm apart with the buds 2.5cm below the soil surface. I'll be potting most of mine up so I can offer a few sea kale plants for sale next year.

I decided to try forcing the remaining root (in the middle of the top photo above) to provide some blanched sea kale shoots for a meal over the winter. This was very easy - all I had to do was plant the root in a large pot of potting compost and upturn a light-excluding pot over it and place it in a coolish, frost-free place. Our cellar is at 51 degrees F at present which is slightly cooler than the RHS recommends for sea kale (59 - 70 degrees F) but I think it will do fine and the shoots should be ready to harvest in a few weeks time.

Potted sea kale root in cellar for forcing
Sea kale for forcing - beside Stew's Woodforde Wherry brew!

That left me with a few bits of lateral roots. Sea kale root is not exactly raved over but it is edible. I was interested to try eating some. Raw, it was quite sweet, just a little fibrous and brought both parsnip and celariac to mind whilst not having the strong tastes of either. I could imagine enjoying it grated with other roots in a winter salad. It seemed to take a long time to become tender when boiled - at least 25 minutes - the taste didn't change. Roasting it was a bit of a disaster the way I did it, more frazzling than roasting, but might well yield good results in more capable hands! If you grow sea kale and are tempted to feast on the root you can find a recipe for sea kale root rostis here.

I think it's also a good time to sow seed. Sea kale seeds come with their own little buoyancy jackets; the spherical structures in the picture below are sea kale fruits - the seed rattles around in an airspace inside  them and the fruit wall has a spongy open texture - all of which enables the seed of wild plants to be carried by the sea to new growing sites.

I think I've probably done better with autumn than spring sowing in the past because the prolonged moisture breaks down the corky fruit wall so that the seed can germinate. You can also break open the fruit before sowing to increase the germination rate. I sow them in a very sandy compost. They don't seem to appreciate transplanting whilst they are young so this year I shall sow two fruits to a pot in individual pots and weed out one if both germinate. Sowing seeds in open ground would be a good idea too - the plants always seem much happier once they can get their roots down.

And you can eat the seeds too! In summer those corky fruits, in the words of Mark Williams in this delightful post on his Galloway Wild Foods blog, "look like peas and taste like cabbage." I must remember to try some next year!

N.B. I sell a range of perennial vegetable plants on my website.