Broccoli is one of the most nutritious vegetables you can grow, and though the average family eats some twenty-six pounds of broccoli a year, only about half of American gardeners grow it. It is a cool-season crop. In the Far North broccoli is grown as a spring-sown, summer-harvested crop, but from USDA zone 4-8 it can be sown both for a spring and fall crop; mid-summer crops do not usually produce heads of sufficient quality to be worth the time and space they occupy. In the Deep South, spring plants should be started before Christmas and set out by Valentine’s Day so that they have a chance to head up before the weather turns hot. Perhaps the best climate for broccoli (and its relatives) in the United States is in the Pacific Northwest, where the combination of cool summers and mild wet winters make broccoli almost a year-round crop.
Since the part of the plant we eat is its flowering shoots, you might think it would belong in the “fruits” part of the rotation. But all the members of the cabbage family, (also known as the brassicas), including broccoli, are relatively nutrient-hungry plants, so we put them in the first year of our rotation, when nutrient levels are at their highest. Also, since the soil-borne diseases to which all brassicas are susceptible are able to survive long periods in the soil, we want to keep all the brassicas in the same part of the rotation, so that the time between repeated plantings in the same plot is maximized.
There are basically two types of broccoli cultivars: those which are adapted for production of a single central sprout, and those which will produce a lot of lateral shoots after the terminal shoot is cut. New research has led to three different methods of growing broccoli, depending on what kind of harvest you want (see below). There are also some unusual forms that sort of span the classification of broccoli and cauliflower — two very closely related plants — and produce purple or orange heads…one Italian type (see photo on left) even produces startling “Fibonacci” heads if grown properly.
Growing Broccoli – Method 1
If what you want is a long harvest of small, eminently usable side shoots, choose a variety that is known to produce a lot of side shoots, and start the plants six to eight weeks before the last frost, and set them out two weeks before the frost-free date, two feet apart in rows spaced three feet apart. In intensive beds like ours that translates to a single row down the center of the bed. Set the plants with their first leaves just above ground level and water them in well. A month or so later, when the central bud begins to form, side-dress the plants with a bit of extra fertilizer; we use a tablespoon of fish emulsion in a gallon of water.
Cut the central head as soon as it reaches three inches across. That will shift the hormonal balance of the plant and send its growth energy to the side, or lateral shoots. Cut that first, early head up high on the stem, to keep from shocking the plant, and do the same with the side shoots so the plant is stimulated to produce as many laterals as possible. In both these cases you need a big plant, so start early and make sure that nothing slows their growth.
Growing Broccoli - Method 2
If you want to go for those big, blue-ribbon heads you’ve seen in the catalogs, start your plants six to eight weeks before the last frost, and set them out two weeks before the frost-free date, two feet apart in rows spaced three feet apart. In intensive beds like ours that translates to a single row down the center of the bed. Set the plants with their first leaves just above ground level and water them in well. A month or so later, when the central bud begins to form, side-dress the plants with a bit of extra fertilizer; we use a tablespoon of fish emulsion in a gallon of water. Let the head grow to full size and cut just before the florets open.
Growing Broccoli - Method 3
If your aim is to get the most broccoli in the least space, with the least effort, here’s how: start five times as many plants, in flats, using a variety that has been selected for producing single shoots. Set them out only eight to twelve inches apart in intensive beds. The individual heads will be much smaller—only about four inches across—and the crop will mature all at once, but if you are freezing broccoli, that’s a boon, and total yields are double that of the regular methods. Just make sure that there is no shortage of nutrients, and be prepared to side-dress with fish emulsion at bud formation time.
This method also works well if you are direct-seeding spring broccoli. You can either sow the seed 1/4-inch deep in rows and thin at the four-leaf stage, or place a few seeds in each spot where you want a plant and then remove all but the strongest once they are established. I’m going to try growing it in hills: I’ll sow eight to ten seeds per hill, with two or three feet between hills, then thin to the strongest five.
In the North, seed fall broccoli ten to twelve weeks before the first fall frosts, but by mid-July at the latest. In mild winter areas of the South, August is the time to plant, but you’ll probably need to shade the beds to help with germination and nurse the plants through their first few weeks. If you wait until the weather cools down, they won’t set buds before temperatures and day lengths get too low to mature a head. October is planting time in the desert Southwest, where much of the country’s winter crop is grown.
Pests and Diseases of Broccoli
We cover our spring broccoli with a floating row cover immediately after sowing or setting out both to temper the weather a bit and to keep off flying insects. Flea beetles can decimate tiny, sprouting seedlings but the real danger to transplants is from the cabbage root maggot. These are the larvae of a small housefly-like insect that appears around the time dogwood trees are in bud. It spends about two weeks laying its eggs at the base of young plants. When the maggots hatch they tunnel into the roots of the broccoli, and in the process do enough damage that the plants wilt or, in severe cases, break off at the ground. Once the plants are infested, it’s hard to do much for them, as removing the larvae involves digging up the plants. Row covers prevent the cabbage fly from reaching the plants to lay her eggs.
My grandfather, gardening before the advent of row covers, used wood ash to control this pest. A few days after transplanting he would sprinkle dry wood ashes around the base of each plant so that the area was completely covered, out to a distance of four inches or so. He didn’t have an explanation as to why this should work, but his garden was proof that it did. My guess is that either the ash, which is highly alkaline, changes the pH of the soil so radically in the exact area where the fly lays her eggs that they won’t hatch, or that the ash is so powdery and dry it desiccates the eggs. It is possible, though, that the ash simply supplied enough potassium to ensure that root growth on his broccoli was vigorous enough to withstand some resident maggots. At least that was the conclusion reportedly reached by Blair Adams, a Washington State researcher who studied the problem some years ago. In fact, he was said to have found that the wood ashes actually attracted cabbage flies!
The other traditional methods of interrupting this fly’s life cycle are collars and mulch. Collars are three to four-inch circles cut from tar paper or cardboard that have a slit from the edge to the center, so that they can be placed on the ground at the base of the plants, completely surrounding the stem and preventing the fly from reaching the soil to lay her eggs. This is the same idea as mulching. While you could simply mulch the entire bed, the most effective material seems to be sawdust. As a whole-bed mulch, sawdust is too acidic and nutrient-hungry, but placed in a six-to eight-inch circle surrounding the stem, at a depth of one to two inches, it prevents the fly from reaching the soil. Hay is not as effective, perhaps because its porosity allows the fly to climb down through it to the soil.
Once the plants are up and growing, their major enemies are the cabbageworms. These are pale green caterpillars, 1 to 1 1/2 inches long, that eat everything cabbagelike in sight, including broccoli. They are the larvae of a number of related species of moths, and the most effective modern control is Bacillus thuringiensis, or Bt (see below).
Before the development of Bt, my grandfather had a great method of controlling cabbageworms: me. My brother and I (and an occasional friend) were given old, warped tennis rackets and paid a bounty of a nickel each for the dusty white butterflies that are the adult form of the cabbageworm that was prevalent in our area. This may still work well if you have energetic kids, or need the exercise yourself, but it’s not the most efficient method out there. You can also hand-pick or crush the eggs before they hatch, but effective control is almost as time-consuming as swatting the butterflies.
Hand-picking is more effective after they hatch, though it means you’ll have to put up with some damage to the plants. Young worms seem to prefer the upper side of the leaves near the midrib, so that’s the easiest time to find and crush them. Later they work their way down the leaves, and they eventually hide inside the head, at which point they are really difficult to control. You can expect to see the first young caterpillars about a week after you notice the moths have arrived in your garden.
Probably the most effective method of controlling these pests is by the use of what old-time organic gardeners call “bug spray,” an unappetizing concoction that uses statistics the way they ought to be used. This is essentially the same technique as using Bt, but it is home-made, and free. Here’s how to make it.
Once the caterpillars appear, find a few that look abnormal or that seem more sluggish than the others (what you are after is sick or parasitized individuals), plus a dozen or so normal ones. If you can’t find any sick ones gather three or four dozen total, the more the better. Now here’s the revolting part: take the caterpillars and put them in an old blender with a cup of tepid water and make bug soup. The water should not be chlorinated; if you are part of a community water system, use water from a pond, stream, or mud puddle. If you don’t have a blender you’re willing to sacrifice for this purpose, you can crush the caterpillars by hand or with a mortar and pestle. Add another cup of tepid water, pour the “soup” into a canning jar and set it in a warm place, say the laundry room, for a couple of days. Then take the contents of the jar, dilute with a further amount of water appropriate to the size of your garden, and put it in a garden sprayer, straining it if necessary. Use this spray to thoroughly coat the leaves of the plants affected. With any luck, the majority of the caterpillars will soon sicken and die.
Why should this work? Because you have “cultured” — using a kitchen-table form of genetic engineering — whatever disease or parasite the sick and dying caterpillars you selected had, and then spread it all over the food supply of the remaining caterpillars. The reason for getting a large number of individuals if none of them look sick is that it is statistically likely that some of them were ill, but just not showing the symptoms. Any parent of school age children will recognize this process immediately! By giving the existing disease good conditions to spread — warm, unsterilized water with crushed caterpillar bodies in it — you helped along a thoroughly natural process, and that is the essence of organic gardening. The principle involved here is simple, and applicable to any number of garden pests, as long as you can catch them at the feeding stage. If this method is too down-and-dirty for you, though, there are commercially prepared biological pesticides available.
Bacillus thuringiensis (Bt) is a naturally occurring bacterium that infects, and eventually kills, a wide range of soft-bodied caterpillars. It is harmless to other kinds of animals, including people (but also to adults of the same species as the caterpillars, which means that timing of applications is critical). If you use this spray, which is sold under a number of trade names such as Dipel or Thuricide, you need to begin spraying within a few days after the butterflies appear, and repeat the sprays every week or two while the butterflies are around, to make sure that none of the eggs hatch onto untreated leaves. Once the caterpillars catch the Bt infection they stop eating, but it takes three or four days for them to die.
There are several seed-borne diseases of the whole cabbage family that affect broccoli, but if you buy quality seed from a reputable seed house they won’t concern you. Club root, however, is a soil-borne fungus that can be brought into your garden on the roots of purchased transplants, or with a load of manure from livestock that fed on infected plants, or even on the soles of your shoes. Its first symptom is wilted plants in the heat of the day that recover overnight. Pull one of the affected plants and look at the roots; the deformity associated with this disease will quickly explain its name! The best way to avoid a repeat (if you do see the symptoms) is to destroy any infected plants and keep all brassica family crops out of that area for at least four years. Seven years is better, though impractical for home gardeners. You can help prevent club root with an application of wood ash around the base of the plants, as that will raise the pH of the soil beyond the range that supports the fungus. For this use, mix the wood ash into the soil instead of just dusting it on the surface.
Whichever method you use, broccoli should be harvested just before the florets open. Cut with a sharp knife, preferably at an angle so that rain or irrigation water can’t collect on top of the cut stem, which could lead to stem rot if the season is wet. With Method 1, keep the buds cut off to extend the harvest, because once the plant begins to flower, it forgets about you and your needs! With Method 2 you can remove the plants immediately after harvest and plant something else; the same is true of Method 3, as both of these are once-over affairs.