One of the great things about gardening on a new plot is discovering what is in the soil. When I took over at Myddelton House, aeons ago, the first year was a voyage of discovery and every month revealed new surprises, rare and beautiful snowdrops in spring, billions of crocus, majestic martagon lilies in large drifts in summer and dense carpets of cyclamen in autumn. It wasn’t a totally smooth journey but there were lots of nice surprises.
This one has been a bumpier ride, starting with the revelation that I have the unholy trinity of weeds; ground elder, bindweed and mare’s tail – oh with a clump of Japanese knotweed thrown in for good measure!
In the walled garden, that has not been intensively cultivated for years, I had hoped that there would not be too many nasties laying in wait for me. Last summer things started well but I then found that carrot root flies had been waiting for me to start growing their favourite food. Onions grew well at first but then I found that some of them were affected by white rot and then I found out I had the full set when clubroot reared it’s ugly head.
When it comes to being difficult, cabbages, along with their cousins; Brussels sprouts, cauliflower, kale, turnips, swede, (or, here in Ireland, white turnips and turnips) calabrese and broccoli, just about win hands down. The things that can go wrong with them is legion. If the slugs and snails don’t eat them as seedlings, the pigeons will have a go, or caterpillars (two species) or whitefly, or mealy aphid or even, if you are unlucky white blister. And as for those cute little bunnies…!
Anyway, last year all was going well when I looked at one batch in a raised bed and they looked a bit stressed and dry. Then their leaves looked a bit purple round the edges, as though they were starved and they just were not growing as they should. Fearing the worst I pulled one up and I was right – I had clubroot.
What is clubroot?
Clubroot is a fascinating thing. It (Plasmodiophora brassicae) is related to fungi and slime mould and infects the roots of all these crops plus wallflowers and stocks as well as related weeds such as shepherd’s purse. As it does so the roots swell and they lose their root hairs so the plants cannot take up water or grow properly. This is bad enough but you should not grow any of these affected plants in the soil until the spores in the soil die through lack of host plant. And the really bad news? That can take up to 20 years!
So what do you do if, like me, you have the disease?
1 Grow spinach
2 Grow your plants in large pots and only plant them out when they are pretty big and they can complete their life cycle before they succumb.
3 Improve drainage. In theory, clubroot is more prevalent in moist conditions and the soil in the garden here is badly drained but this happened in a raised bed in dry weather so that is not a cure.
4 Add lime to the soil. Clubroot thrives in acid soil. The soil here is acid and probably has not been limed for many years. The beds the clubroot was in had not been improved before planting (most of the garden had mushroom compost added). I have now made a new brassica bed which has been fallow for years and I have added lime. I also use and will use calcified seaweed (substitute).
5 Grow resistant varieties. Thank you plant breeders. Thanks to you we now have resistant cabbages and cauliflowers such as ‘Kilaton’ (http://www.unwins.co.uk/cabbage-kilaton-seeds-pid3913.html ), ‘Clarify’ (http://www.unwins.co.uk/cauliflower-clarify-seeds-pid3927.html )and ‘Clapton’ (http://www.suttons.co.uk/Gardening/Vegetable+Seeds/Popular+Vegetable+Seeds/Cauliflower+Seeds/Cauliflower+Clapton+F1_158233.htm ).
There is no chemical control of clubroot.
Free is not good value
Clubroot is usually worse on allotments than in gardens because you can spread the disease from one area to another simply on your boots or if you accept diseased plants from a fellow gardener. Always by or accept plants that have been grown in pots or trays, not from the soil (and that can include wallflowers).