I recently had a question about nasturtiums (Tropaeolum majus). A lot of gardeners don’t bother with these ‘easy’ annuals, leaving them for kids to grow. Anything so ridiculously easy to grow is not really suitable for serious gardeners, is it? I do use them here and there and, although they can self-seed too freely, I appreciate their volunteer seedlings, many of which I leave to grow. They are easy to identify and to pull out unwanted seedlings.
But are they actually easy to grow? The gist of this enquiry was ‘Over the last couple of years, I have nothing but disasters with my nasturtiums. One year black fly devastated them, and then cabbage white butterfly caterpillars destroyed them. This year I appear to have yet another problem, but I am not sure what is causing this.’
You can’t see the latest problem but it looked as though they were battered by wind or cold and the reason was probably caused by the plants being grown under cover, possibly on a windowsill, and then being planted out without being ‘hardened off’. Any ‘soft’ plant, coddled in warm, low-light conditions and then planted outside without being conditioned. can be damaged by cold, wind or scorching sun. Often the plants recover but it can be a check to growth. But back to nasturtiums specifically.
Because the plants contain similar, sulphurous chemicals to brassicas (to which they are not related), they attract some of the same pests. [the common name nasturtium is the same as the botanical name for watercress – which is a brassica – and means ‘nose twister’ because of the peppery taste – of both].
So nasturtiums are prone to cabbage white caterpillars and blackfly (aphids). I think that part of the problem lies in the oft-given advice that nasturtiums should be grown in poor, dry soil. This dates back to older kinds that have large leaves. Because they had large leaves, when grown in rich soil the leaves swamped the flowers, which were on short stems. This didn’t bother the bumblebees which flit among the flowers under the canopy but it does reduce their colourful impact in the garden. Plant breeders have worked hard to improve this state of affairs, most notably with the, now old, ‘Gleam’ hybrids with flowers that are better displayed. If you browse through any seed catalogue you can see new nasturtiums added every year so they must be more popular than I intuitively believe. There are now very dwarf kinds and the range of flower colours is quite compelling – who wouldn’t want to grow them?
Much of this is surely because of the belief that they are easy to grow and partly because they are the most edible of the edible flowers, which you would believe, if you listen to TV chefs, are an essential part of any meal! Take a piece of meat, vacuum-pack it in plastic, put it in a water bath so it is luke warm, throw away the plastic, flick a blow torch over it, burn a lettuce, cut tiny spheres out of an apple and compress them in another plastic bag and chuck the rest away, shave truffle on top, cover it in ‘cat sick’ (foam) and two drops of the litre of tarragon oil you made and sprinkle on some begonia flowers (and call them apple blossom if it is Masterchef) and voila – a Michelin star! Yes – can you tell it bugs me!
So we don’t need to grow nasturtiums in the poorest soil because they are now likely to be colourful even in rich soil. And then they will be less stressed and less likely to suffer from pests. But it remains a fact that these plants do get attacked by aphids and caterpillars. It is for this reason that they are often suggested for companion planting – planted among cabbage they may attract the butterflies away from your crop onto the ‘sacrificial’ nasturtiums. I am not sure. I will not get started on companion planting. But if you like the idea then give it a go – dwarf nasturtiums are unlikely to smother or harm cabbages and are better than bare soil.
Having said all this, although I did have some blackfly on nasturtiums in the first year, in this garden, I have not had the problem for the past two years and last year I didn’t even have any on the broad beans. And I had more nasturtiums in the garden last year than any other year and there was not even any caterpillars, though there were on the brassicas. How do I explain this? Well the nasturtiums are all in good soil or, in the case of the raised bed at the top of this post, well watered and fed. Maybe it is because I don’t spray (except for lily beetle when necessary) and I feed the birds. Blue- and great tits flit among the shrubs in the garden all year round. I have a spindle tree (Euonymus europaeus) in the garden that is the winter host of the black bean aphid. But I suspect that the tits eat these over the winter. I noticed overwintered aphids in clusters on a twisted willow last year, in dense clusters on the stems, but they were gone by spring. Although I often seem sceptical about ‘green gardening’, I am sure that tits and wrens are useful in the garden, mopping up insects – probably both good and bad.
I have rambled. The quick answer to the original question is that nasturtiums are generally easy but don’t abuse them just because they are easy. Give them a decent chance and if you do raise them under cover, harden them off gradually before planting them out in the garden.
And one more point. Although they are often classified as hardy annuals, they are killed, stone dead, by frost. The seeds will survive freezing soil, and they will self seed, but if seedlings appear too early, or if plants are put out too early in spring these will die.