The brassicas are a huge component of vegetable gardens: many, many of our garden vegetables are in this family. These plants are also sometimes called “crucifers” or “coles”. Included are:
many other Asian greens
and probably others I can’t remember at the moment
Most gardeners want to be able to grow at least some of these plants: their absence makes a huge hole in the vegetable garden as well as in the diet, as many of them are nutritional powerhouses. Many are also really delicious when home-grown.
The brassicas are, basically, cool season (spring and fall) plants although there are some that can be coaxed along through summer, certainly in areas with relatively cool summers. I can grow mizuna, other Asian greens, collards, bok choy, broccoli and others through the summers here in northern Pennsylvania in the mountains. But I don’t think it could be done in, say, Georgia. The hot-summer places typically have longer springs and falls, though, so that affords sufficient time to grow these plants in those areas.
Brassicas are occasionally subject to some nasty soil-borne problems but as a container gardener, you avoid those completely. They are also subject to damage from flea beetles, but – at least in my experience – flea beetles stay close to the ground and do not jump high enough to pester container-grown plants. (I have had no flea beetle damage in container-grown plants: none, zero, never.) So right away, you’re ahead of the game.
However, even container-grown brassicas are subject to the depredations of Evil Butterflies and Evil Moths! (Enter the villains of the piece….). The cabbage looper moth and the cabbage butterfly cause the same problem, and the solutions are the same too – a solution effective for one is also effective for the other – so I’m mostly just going to refer to them both as “cabbage butterflies.”
Brassicas and cabbage family plants
You may see small white butterflies flitting innocently and delicately over your plants. Them’s the bad guys! (You’re less apt to see the moths as they do their evil business at night). The butterfly (or moth) lays eggs on the brassicas. The eggs hatch into larvae (worms or caterpillars). The larvae of both the butterfly and moth are green, by the way. These larvae eat the leaves of the plants. Left alone, they will completely destroy the plants. When the leaves are sufficiently riddled with holes, the plants collapses and dies.
This is one of the very few insect problems that container gardeners really need to solve. I have spoken with gardeners who claim that they never have this problem. I think they’re very lucky indeed, or maybe their area has some unusual climatic or geographic feature that prevents the butterflies from living there. I can only say that I have experienced the Evil Butterfly Problem in Delaware, New Jersey, and Pennsylvania (places in which I’ve grown brassicas), and in containers as well as in the in-ground garden. The Encyclopedia of Natural Insect and Disease Control states that all 50 states in the USA have them (even Alaska!), so presumably Canada is troubled by them as well. I don’t know whether they exist on other continents or not.
Fortunately, there are three fairly simple things that will solve the problem and none of them involve the use of broad-spectrum insecticides or heavy chemicals. I use all three solutions: which one I use depends on the circumstances. So I’ll tell you about all three solutions and you can choose the solution(s) that seems suitable for your circumstances.
First, some brassicas can be planted in early enough spring that you’ll harvest them before the butterflies appear. I can do this with several of the very fast growing Asian greens such as baby bok choy, choy sum, and hon tai tsai. I think you could do it with radishes too (I seldom bother to grow radishes, however, as I don’t like them much.) You can also grow some plants late into fall and winter (kale, for one) after the butterflies have left for the season or gone into dormancy or died off (whatever butterflies do when the weather turns cold). So this is one solution.
Second, you can spray your plants with a solution containing Bacillus thuringiensis, usually abbreviated as Bt. Bt is a bacteria that infects and kills the larvae of butterflies and moths. It is harmless to other organisms (including humans). Bt can be sprayed on your plants up to the day you harvest them. You do need to spray the Bt at the correct point in the larvae’s life cycle, so if you use this solution, read the label and follow the directions. It may need to be resprayed after rain, too.
Bt is available from GardensAlive, other online sources, and local garden centers. This is my solution of choice for decorative containers: containers that I want to look pretty. It’s effective, it works, it’s a fine solution to a nasty problem.
The third solution is what I usually use: that is, to cover the plants with either floating row cover or nylon netting. The openings in the nylon net are small enough to keep out the butterflies and moths, so in this case it works just as well as the row cover. Nylon net is also cheap and available in fabric stores and the fabric department of discount department stores. Row cover comes in fairly large quantities, perhaps more than you, as a container gardener, would want, so the nylon net would be a better choice for you in that case.
In the case of the brassicas, we don’t want pollination: we don’t need these plants to produce fruit as we eat the leaves (cabbage, etc.), flower buds (broccoli, etc.), stalks and leaves (bok choy, etc.) or roots (turnips, etc.). Since we don’t need bees or other insects pollinating these plants, the netting or row covering can be left on throughout the entire life cycle of the plants, just being pulled back for harvesting. You can water right through either row covering or nylon net, and sunlight will enter through the coverings too, so that’s not a problem.
You can drape floating row cover loosely directly over the plants, fastening it loosely down at the edges with soil or with ground staples (long u-shaped pieces of heavy wire). For containers, you can also clothespin it to the container’s rim. The plants will push it up as they grow. I don’t like to do this though, because I believe it restricts the plant’s growth somewhat and encourages mold and fungus by being closely draped around the plant and soil, especially in a wet season.
So this is what I do for container plants that need to be covered: I make a cage that will fit just inside the container’s rim. I use 1″ mesh chicken wire to make these cages. The 1″ mesh chicken wire is self-supporting (2″ mesh chicken wire is too floppy for this purpose). I make the cage taller than the plant will eventually grow. For the sake of simplicity, I have standardized on using 3′ chicken wire although in the case of some of the brassicas you could manage with 2′ chicken wire. The chicken wire cages are reusable for successive seasons, and the netting or row cover is also reusable. If you have no chicken wire, but have some woven wire fencing left from a project, or tomato cage wire, they would also work here. Or you could construct a frame out of light pieces of wood. You just need something that will support the netting or row cover.
I put the cage inside the container when I transplant the little plants out, fastening the cage down to the soil with ground staples. I then cover the cage (right away!) with nylon net or floating row cover. I fasten the net or row cover to the soil in the container with ground staples at the bottom, or I use clothes pins (UK: clothes pegs) to fasten the net to the container rim. I fasten the net to the cage’s top with clothes pins. Voila! The Evil Butterflies can flutter all around the container, but they’re not going to get in to lay their eggs on my plants. Villains foiled, problem solved!
So there you have it: three different ways to solve this problem: all are very effective. You may want to use all three (as I do), choosing which is best on a case-by-case basis.