Brassica oleracea var. Botrytis
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You may have heard that it’s difficult to grow, but that’s only because it has specific requirements that need to be met in order to produce robust and delicious flower heads. Read on to learn what they are!
What You’ll Learn
- Colorful and Nutritious
- Growing a Winner
- Pests and Disease
- Meeting the Challenges
Colorful and Nutritious
Cauliflower is a cool-weather crop often referred to as a “brassica” or “cole crop.” It has edible leaves, stems, and dense flower heads that are a substantial source of B, C, and K vitamins and fiber.
The flower heads are made up of many tiny buds, or “curds” that are eaten before they bloom. A cross-like, four-petaled blossom inside each bud further classifies cauliflower as a “cruciferous” vegetable.
Folks have been growing white flower head varieties for generations, but today we also have vibrant green, orange, and purple cultivars. Purple curds contain the antioxidant anthocyanin, and orange, or “cheddar,” as they are commonly known, are rich in beta carotene, an excellent source of vitamin A.
Let’s find out how to plant for success!
Growing a Winner
Growing cauliflower reminds me of “Goldilocks and the Three Bears” and their bowls of porridge. This veggie doesn’t like air that’s too hot or too cold, preferring instead temperatures that are consistently “just right.”
If you’re in a zone where you have two to three months of temps that average in the 60s, you’re in prime cauliflower-growing territory. The rest of us must work a bit harder.
A Cool Annual
Cauliflower is a half-hardy biennial that is usually grown as an annual in USDA Hardiness Zones 2 to 11.
How confusing is that?
Half-hardy means it’s able to withstand some frost. The leaves may “burn,” but a maturing flower head may continue to grow. However, if a cold spell comes suddenly, the temperature fluctuation may cause a plant to bolt, finishing its life cycle prematurely, and likely producing an inedible crop. And a biennial is a plant that takes two seasons to mature. However, if cauliflower gets the cool weather it craves, and produces a flower head in one season, it’s an annual.
The number of days to maturity varies from approximately 50 to 100, so pay close attention to seed packets when making your selections. Choose a length of time that suits your average weather.
In warm climates, plant in the fall for an early spring crop. In colder zones, you have the option of planting indoors in early spring, or outdoors in late summer, to avoid peak heat and cold.
Here in Southeastern Pennsylvania, we sometimes have crazy days in April when temperatures suddenly soar to 90 ° F. This may cause plants to” button,” producing multiple tiny heads, or “bolt,” forming curds that spread and go to seed. It’s much better to plant in late summer for a fall crop in locations like mine.
For an early summer harvest, Rodale’s Ultimate Encyclopedia of Organic Gardening recommends starting seeds indoors in peat pots about four to six weeks before the last expected frost date.
Sow seeds 1/4- to 1/2-inch deep in peat pots. This way, you can plant entire pots instead of plucked seedlings, and avoid root damage. Be sure to use sanitary tools and supplies to avoid exposing your germinating seeds to disease.
Place the pots on a 70° F warming tray and set it near the sunniest window in your home. Keep the soil moist, but not soggy.
And as we’ve said, in cool climates, you may also sow seeds in late summer for a fall harvest. Place them directly in the ground two to three months before the average first frost date.
When the seedlings have sprouted not only cotyledons, or “seed” leaves, but several sets of true leaves, begin to “harden them off.” This simply means setting the pots outside for a few hours each day, increasing to all day, before transplanting them into the garden.
Choose a planting location with full sun to partial shade. Full sun is recommended by many seed packets however, a partially shaded placement offers protection in the event of a sudden spike in temperature.
You may want to have a soil sample tested to determine its acidity and nutrient content. Soil with a nearly neutral to slightly acidic pH is best. Transplant during a cool time of the day, morning or evening.
Preparing the Soil
Cauliflower does best in good soil that drains well. Per the results of your test, you may work amendments such as organically-rich compost, bone meal, or lime into it as recommended by the testing laboratory.
Work your soil to a depth of at least six inches. Plant entire peat pots at least 24 inches apart. Some seed packets recommend closer plantings, but this doesn’t allow for maximum air circulation. Mature plants generally reach a height and girth of about two feet, and overcrowding increases vulnerability to pests and disease.
Theories differ on fertilizer. Carla Emery, in her comprehensive Encyclopedia of Country Living, warns against commercial fertilizers that may burn cauliflower’s tender roots. Her instructive book is available from Amazon.
The folks at the Missouri Botanical Garden recommend high-nitrogen varieties.
And the pros at the University of Nebraska-Lincoln Institute of Agriculture and Natural Resources Nebraska Extension recommend using phosphorus-rich 33-0-0 starter fertilizer at transplant time, with a side-dressing three weeks later.
I like a slow-release all-purpose granular type like Miracle-Gro Shake ‘N Feed All Purpose Continuous Release Plant Food, a balanced nutrient supplement that promises not to burn roots if used as directed. It’s available from Amazon in 4.5- and 8-pound containers. Apply it at transplant time, and it works throughout the growing season.
If you choose to fertilize and don’t use a slow-release product, apply it at transplant, and then as a side dressing per package instructions during the growing season. Side dressing is simply applying it around the perimeter of plants, just outside the edge of the largest leaves, to avoid direct contact with foliage.
Cauliflower requires even moisture, so don’t let it dry out. To increase moisture retention, make a narrow moat around each plant by mounding soil up in a ridge around it. Mix some mulch into this soil ridge to further aid in moisture retention, protect delicate roots, keep the ground cool, and inhibit weed growth. The less you weed, the better, as the roots are shallow and fragile.
Water deeply once a week with a gentle spray nozzle aimed at the soil over the roots. Do this in the morning or evening, when temperatures are at their coolest. Watering by hand plus rainfall should amount to between one and two inches per week.
In early spring, most of your garden is likely to be in full sun, however, as the season comes into full bloom, trees begin to leaf out and cast some shade.
Consider this as you choose a planting site. If partial shade is unavailable, be prepared with a supply of lightweight floating row covers that you can quickly set up if the sun’s rays become intense. Place them as high as possible and leave the ends of the rows open to ensure adequate air circulation.
For fall crops, the converse is true. Cold snaps are not uncommon, so keep row covers of a heavier material on hand. Place them a little lower and close off the ends, to create a snug environment. Be sure to open the ends or remove them entirely when temps rise.
In addition to providing some temperature control, row covers help deter unwanted pests.
Pests and Disease
As with all cabbage relatives, cauliflower is prone to pests and disease, posing another challenge to successful growing.
If you notice discoloration, wilting, or holes in the leaves; damage to stems or roots; insect infestation or eggs, take immediate action. Some pests may reduce leaves to skeletons before burrowing into flower heads, while others attack at the root level. And pests are a primary source of the spread of disease.
Here are some pests you may encounter:
The aphid is a tiny, sap-sucking insect that eats through leaves and flower heads.
It spreads plant diseases and leave a trail of honeydew that promotes the growth of a fungus called sooty mold. If you see eggs on the undersides of leaves, and tell-tale clumps of stacked up aphids, try to rinse them away with a steady and stream of water.
If this prove ineffective, use a product such as neem oil, a natural insecticide and fungicide. It’s available from Amazon in a variety of sizes.
For further reading on organic methods to deter this insect pest, consult our article on aphids.
The cabbage looper, Trichoplusia ni, is a leafeater that can chew a crop down to nothing in no time.
Per the pros in the University of California Agriculture and Natural Resources Statewide Integrated Pest Management System, this green caterpillar is unmistakable, with its distinctive inch-worm-like gait, green body, and white stripe. Adults are brown moths with a distinguishing silver figure eight, and eggs laid on the undersides of leaves are domed and ridged.
Cabbage loopers do their worst damage to mature plants, tearing through leaves and right into the flower heads. A treatment with organic Bacillus thuringiensis is recommended. It won’t hurt beneficial insects like the tachinid fly, that feeds on several caterpillar pests.
Thuricide by Bonide is available from Amazon in concentrated liquid form in 8-ounce bottles.
Or, you may try a home remedy by Sharon Lovejoy, horticulturist and author of Trowel & Error (see it on Amazon), a collection of gardening tips. She recommends dousing plants with white flour (not self-rising) early in the morning. Dew plus flour equals petrified bugs that may be rinsed off the following day.
Per the experts at the Michigan State University’s MSU Extension, the cabbage moth, aka Diamondback moth, Plutella xylostella, is one of the most destructive insects when it comes to brassica crops.
Easily recognized by the white diamond visible on its folded brown wings, the larva and adult of this species are voracious feeders that decimate entire plants. If you notice the moth, look for eggs on the undersides of leaves.
This is a difficult insect to deal with, as it has developed resistance to some pesticides. Natural predators include the parasitic wasp, a beneficial insect. Try neem oil or Bacillus thuringiensis, but you may find them ineffective.
You may also try a practice called “trap cropping,” as recommended by the University of Connecticut Pest Management Program Department of Plant Science and Landscape Architecture, Department of Extension. This practice involves planting a barrier of another plant the pest likes around your brassica. In this case, collard greens are recommended.
The idea is that the cabbage moths will chew the collards to bits before attacking your cauliflower. Best case scenario – you enjoy both crops at harvest time.
Cabbage Root Fly
If you see an inordinate number of flies around your crops, apply diatomaceous earth to the soil over the roots to discourage egg laying. And if your plants are showing signs of distress, dig down, examine the roots, and discard infested plants.
Alternatively, you may try an application of nematodes, microscopic worms that attack soil-borne pests. Bug Sales Live Beneficial Nematodes are available from Amazon in packages containing from 5 to 250 million.
There’s something else you may want to try – a cabbage collar. This is a circle of felt, cardboard, or a similar material that goes around a plant at the soil level to prevent flies from laying eggs near the roots. Find it in garden centers or make your own.
Cabbage White Caterpillar
The cabbage white butterfly, Pieris rapae, lays eggs that become voracious larvae.
Also called cabbage worms or imported cabbage worms, these caterpillars devour leaves and bore into flower heads, ruining entire crops.
Bacillus thuringiensis or pyrethrum are the treatments of choice for this pest.
PyGanic Gardening’s Botanical Insecticide Pyrethrin Concentrate for Organic Gardening is available from Amazon in 8-ounce bottles.
Another pest you may see is the cabbage whitefly, Aleyrodes proletella. This tiny white fly and its young scaly nymphs infest the undersides of leaves, feeding on leaf sap, excreting “honeydew” that promotes sooty mold growth.
But while this type of whitefly disfigures a plant’s leaves, it doesn’t damage the flower heads, so many growers simply put up with it.
The Royal Horticultural Society is of the opinion that unless an infestation is severe, it probably doesn’t need to be addressed with pesticides. However, if you go that route, know that treating the undersides of leaves is a temporary fix, and product instructions must be followed diligently with reference to the right one for the right crop, as well as safe harvest intervals.
Per the pros at the University of Massachusetts Amherst Center for Agriculture, Food, and the Environment, the cross-striped cabbage worm, Evergestis rimosalis, is easily distinguished from other brassica pests in the egg stage because it is the only species to lay eggs in clusters.
This caterpillar is blue-gray with black stripes on top, and solid green underneath. It feeds on leaves and works its way into flower heads, before maturing to the brown moth you may notice fluttering around your plants.
The crucifer flea beetle, Phyllotreta cruciferae, and the striped flea beetle, Phyllotreta striolata, chew holes in the leaves of brassicas that don’t pierce all the way through the leaves.
The Virginia Cooperative Extension says you can recognize them by their extra-large hind leg that enables them to jump like a flea. Pyrethroid foliar sprays are the recommended chemical treatment. There is no organic product for flea beetles, so the Extension recommends row covers, or planting around the life cycle of the beetles, avoiding their peak feeding time (that’s May to June in Virginia).
You may also try a practice called “trap cropping,” as recommended by the University of Connecticut Pest Management Program Department of Plant Science and Landscape Architecture, Department of Extension and mentioned above. It involves the planting of mustard, a favorite of flea beetles, as a first line of defense.
In addition to pests, there are diseases to which brassicas are prone, including:
Blackleg, Leptosphaeria maculans, is a fungus that causes erosion of leaves, stem blackening, and root rotting. It may affect plants as young as seedling stage. The best ways to avoid blackleg are with quality, disease-free seed, good drainage and air circulation, and regular crop rotation.
You may try an application of a fungicide like concentrated Organocide Plant Doctor Systemic Fungicde, which is available from Amazon in 1-pint and 1-quart containers.
Clubroot, Plasmodiophora brassicae, is a fungal disease that likes acidic, moist soil. It causes roots to fill with mold spores that deform them into ineffective, club-like appendages. If you find your plants failing and dig down to find smelly, slippery, deformed roots, remove entire plants and discard them in the trash. And as this is a pathogen that lives in soil, don’t plant brassicas in the same location next year.
Be sure your soil is not overly acidic, and that it drains well. A fungicide such as mentioned above may be worth a try before declaring a total loss.
Brassica seedlings may fall victim to various soil-borne fungi like Pythium and Phytophthora that feed on roots and stems. Everything may be fine one day, and the next, your new shoots keel over and die a slimy death.
The best ways to avoid damping off are by using clean containers with good drainage and providing good air circulation between plants. You may even find seeds that are pre-treated with fungicide. Otherwise, once the damage is done, no treatment will help.
Downy mildew, Peronospora parasitica, is a fungus with the ability to destroy crops. Per the folks in the University of California Agriculture & Natural Resources Statewide Integrated Pest Management System, the telltale signs to watch for are yellow patches that turn brown, and fluffy white on the undersides of leaves. Infected seedlings may not survive damage to their cotyledons (first leaves), and disease progression leads to stem and flower head damage.
If your plants show signs of trouble, try a product like Safer Gro Mildew Cure. This is an organic fungicide that is available from Amazon in 16-ounce bottles of concentrated liquid.
There are quite a few pests and diseases lurking in the garden, but you’re not alone out there. Beneficial insects and hungry birds are your best friends when it comes to devouring pests and preventing the transfer of disease from plant to plant.
Inspect your brassicas regularly for signs of trouble. Consider using row covers as a preventative measure, and discard severely infested plants by throwing them away, not composting them.
Sanitize tools after use when dealing with infestations, and rotate crops to new locations every year, because pests winter over and stand ready to attack the next crop that comes along.
Not sure what is affecting your crop?
As your brassica crops grow, the leaves will become voluminous, and in the center of each plant, you’ll see a flower head beginning to form.
When it’s a few inches across, it may be time to “blanch.” This is a simple task that involves binding the leaves up and over the developing head to keep the color pristine and the flavor at its peak.
Some cultivars are self-blanching, with leaves that curl naturally up and over the flower heads. Others must be manipulated manually.
To blanch cauliflower, simply gather the leaves in your hands as if you were making a bouquet and bind them together above the flower head. Use rubber bands or twine and be sure to leave room for air circulation. The idea isn’t to snug them up, but to shade them.
Peek in and check on them every couple of days. It may be another week or more before heads reach the diameter specified on seed packets, at which time you may unbind the leaves and prepare to harvest.
Use seed packet information as your guide to the approximate number of days to maturity, and head size. When these benchmarks have been reached, and you have large a large head of dense, closed buds, it’s time to harvest.
Make a clean cut across the stem a few inches below the head.
Some folks like to leave a good length of stem and some leaves attached, as they are good to eat. Others leave most of the stem and all the leaves behind with the hope that side shoots may sprout. While this is likely with broccoli, cauliflower is usually a one-and-done plant.
Meeting the Challenges
In addition to growing in the garden, the plant’s shallow roots make it a good container crop. Just remember that it must have consistently moist soil, and this poses an additional challenge, as a container dries out faster than ground soil.
When you select cauliflower seeds, gauge the length of time your climate stays “just right” for plants to mature. And while it may be tempting to choose one of today’s fast-maturing cultivars for spring planting and a summer harvest, some folks swear that a fall crop of a tried and true slow-growing variety is the only way to go when it comes to the best temperatures and outstanding flavor.
Protect your crops from the start with quality seed and sanitary practices. Sow in soil that’s not too acidic, ensure adequate drainage and air circulation, and consider using row covers for an added layer of protection from pests and disease.
Make room for a few cauliflower plants in the vegetable garden this year. You know how to meet the challenges and are ready for success.
Want more information on growing cauliflower? Be sure to check out all of our guides including:
- The 13 Best Cauliflower Varieties for the Home Veggie Garden
- Why Is My Cauliflower Turning Purple?
- 9 Cauliflower Head Disorders and How to Avoid Them
- Why Is My Cauliflower Fuzzy? Troubleshooting Tips for Ricing in Curds
About Nan Schiller
Nan Schiller is a writer with deep roots in the soil of southeastern Pennsylvania. Her background includes landscape and floral design, a BS in business from Villanova University, and a Certificate of Merit in floral design from Longwood Gardens. An advocate of organic gardening with native plants, she’s always got dirt under her nails and freckles on her nose. With wit and hopefully some wisdom, she shares what she’s learned and is always ready to dig into a new project!