11 Reasons Why Your Cauliflower May Not Form Heads

Brassica oleracea var. botrytis

Cauliflower can be a challenging vegetable to grow in the home garden. It has very specific needs, and when they aren’t met, your harvest basket may be full of green leaves, but no heads. And while the foliage is delicious, it’s a disappointing season finale.

A close up of a cauliflower plant with large dark green leaves on the outside, with smaller leaves in the center but no sign of a head forming. To the center and bottom of the frame is green and white text.

In this article, we’ll consider 11 reasons for cauliflower not forming heads.

1. Wrong Seed

Sometimes a crop is doomed from the start. This is likely to be the case when you purchase seed that is not suited to your USDA Hardiness Zone. Cauliflower thrives best with consistent temperatures ranging from 60 to 70°F.

A close up image of light brown cauliflower seeds on a green background, fading to soft focus at the edges of the frame.

Be sure to read seed packets carefully and choose varieties with days to maturity that match your climate’s growing season. Decide if you’ll plant a spring or fall crop, or both. Explore the latest cultivars that have improved temperature tolerance and shortened maturation periods.

2. Seedling Stress

Cauliflower is temperamental throughout its development, especially during the germination and seedling phase.

For best results, start seeds indoors about four to six weeks before the last predicted frost date in spring. This is preferable to direct sowing, because it gives seedlings a chance to become established before facing outdoor conditions.

A hand from the right of the frame, with a dark blue gardening glove is holding a cauliflower seedling over a freshly dug hole, ready for planting. In the background are further seedlings and soil in soft focus.

Transplant seedlings about two weeks prior to the last average frost date in your area, when they have grown at least two sets of true leaves. The ground should be at least 50°F.

Don’t wait too long to transplant, or your seedlings may become pot-bound, with roots that wrap around and around fail to deliver water and essential nutrients to the developing plant

If your climate allows for a fall crop, wait until the average air temperature has dropped to at least 75°F, generally about eight weeks before the first frost.

Seedlings require a period of gradual acclimation to the outdoors called “hardening off.” Without it, cold shock may slow growth and have a detrimental effect on development.

Poorly tended seedlings may appear to thrive, but if they have suffered stress they might not form heads as expected.

3. Lack of Sun

Members of the Brassica genus like cauliflower, broccoli, cabbage, and kohlrabi require full sun to thrive. Without at least six hours of sunlight per day, results may be disappointing.

A close up of a small cauliflower seedling planted in rich dark earth in bright sunlight. The background is soft focus soil.

If your region has afternoons that are really too hot for cauliflower growing, you may try planting in partial shade. However, growth slows without sunlight, and you might find your plants are still putting on leaves when they should be forming heads.

4. Soil Deficiencies

Organically-rich soil is best for cauliflower. It’s a heavy feeder, so do a soil test and determine the nutrient content of your garden. Improve the soil as needed with the addition of compost, well-aged manure, or humus.

A close up, top down picture of a bright green cauliflower seedling in the ground, in bright sunlight. The bright green of the foliage contrasts with the dark earthy soil.

Soil contains macronutrients like nitrogen, phosphorous, and potassium, the N-P-K that you see on fertilizer labels. It also contains other macronutrients including calcium, and micronutrients such as copper. Micronutrients are typically found in lesser amounts.

Imbalances in the soil may result in inadequate nutrient uptake, resulting in stress that may cause failure to form heads.

One nutrient that’s difficult to measure is nitrogen. While cauliflower uses a good bit of it to grow, too much of this macronutrient is known to cause excess foliage production.

Therefore, if you fertilize your vegetables, you should choose a slow-release type in which the ratio of N is slightly less than the P and K components.

A soil test also determines pH, and serves as a measure of acidity or alkalinity. For cauliflower, the pH should be neutral to slightly acidic, or about 6.5 to 7.0. You may increase acidity with the addition of rich organic matter, or decrease it with an application of garden lime.

Poor soil that is devoid of nutritive organic matter, as well as soil with a pH that’s too acidic or too alkaline, may contribute to head formation failure.

5. Inadequate Drainage

While cauliflower requires consistent moisture, it should never stand in a puddle. Its roots need to take what they require to nourish the plant and let the rest drain away.

Poorly draining soil leaves roots vulnerable to nibbling nematodes, slugs, and snails that can impair the ability of the plant to take up water and nutrients. In addition, these insects may spread diseases to weakened plants.

If your cauliflower has consistently wet feet, it may fail to produce heads.

6. Insufficient Moisture

This veggie is one of the thirstier ones. It needs one to two inches of water each week, so get yourself a rain gauge to monitor rainfall, and prepare to supplement as needed.

To the right of the frame a hand holding a hosepipe with a spray attachment watering a newly planted cauliflower seedling into dark rich earth. To the left of the frame is a black plastic punnet with further seedlings ready to plant. The background is soil in soft focus.

With some vegetables, you can get away with keeping them moist during the germination and seedling phases, and then let Mother Nature provide the rain they need.

But this is not so with cauliflower. If you let it dry out, it’s likely to suffer stress that can lead to bolting, buttoning, or no head formation.

Keep in mind that it’s not only a lack of sufficient rainfall and failure to irrigate with supplemental water as needed that may leave your crops at risk of drying out. Wind may accelerate moisture evaporation as well. So, if the weather forecast is a gusty one, protect plants with well-anchored floating row covers.

7. Overcrowding

When transplanting seedlings, space them out with 24 inches between plants, and 30 to 36 inches between rows. This allows for ample airflow and root formation, essentials for healthy growth.

Two rows of cauliflower plants growing in the garden, in between the rows is soil, contrasting with the green leaves. The background is vegetation in soft focus, and the image is bathed in light sunshine.

Circulating air stays cooler and less humid, helping to inhibit fungal diseases that are detrimental to cole crop development.

Roots that can spread without competition from neighbors are better able to hydrate and nourish a plant.

8. Pests and Disease

Healthy plants are less vulnerable to the ravages of infestation or infection.

A close up of a cauliflower plant with its foliage damaged by pests. The leaves are pock marked and have holes in them. The background is vegetation in soft focus.

In addition to meeting light, soil, water, drainage, temperature, and spacing requirements, cauliflower growers need to be vigilant about keeping weeds to a minimum. Thick weed growth creates competition for water, and invites insects who can hide out and be near their favorite vegetable at the same time.

Please consult our article on growing cauliflower for details on how to manage common pests and diseases, as they can cause enough stress to result in failure to form heads.

9. Failure to Rotate Crops

Rotating crops isn’t just for farmers.

Growing vegetables feed on soil throughout the growing season, depleting its nutrients. Changing locations from season to season allows soil to replenish. As an added bonus, it also helps to keep pests and disease at bay.

If you’re not rotating your crops, your soil may become spent, and thus unable to provide adequate nutrition with poor head formation as a result.

10. Immaturity

Sometimes what seems like a plant’s failure to form a head is actually due to a misunderstanding of the number of days to maturity.

A close up, top down picture of green cauliflower foliage, the white veins and stems clearly visible against the light green of the leaves.

Depending on the variety, cauliflower needs between 50 and 100 growing days to be harvest-ready.

While this information is provided on seed packets, it’s easy to forget. If you’ve met the plants’ needs so far, be patient and hope for the best.

11. Temperature Fluctuations

You need to be a bit of a weather junkie to grow good cauliflower, because this is one stubborn vegetable. It just won’t budge when it comes to demanding temperatures that aren’t too cold or too hot.

So, once you’ve chosen seed that’s appropriate for your region, monitor weather predictions and be proactive.

Mulch is going to be your new best friend. It keeps plants cool when the weather warms up, and retains heat when temperatures dip. It also helps with moisture retention.

In addition to mulch, you could place lightweight shade cloth over plants to deflect the sun’s rays during a heatwave.

And conversely, during a cold snap, use floating row covers with their ends snugly closed to form a warm cocoon. These also inhibit wind-driven moisture evaporation.

Favorable Odds for a Successful Crop (With a Bonus Tip)

At any stage from seedling to flush with foliage, a cauliflower plant may experience stress that could alter the course and outcome of its development.

A top down close up image of a cauliflower plant with a very small head developing, between the small leaves in the center of the plant. The white of the head contrasts with the deep green foliage.

Along the way, you might have plants bolt in the heat and go to seed. Or, they may button or rice, leaving you with loose little curds. And finally, they could fail to set a head altogether.

Despite these challenges, or maybe because of them, cauliflower’s allure for home gardeners is strong. Knowing the 11 potential problems outlined above – and avoiding them – puts you ahead of the game.

When you finally see the crowning glory of your efforts nestled in the voluminous foliage, go back to that seed packet and see if you have a self-blanching kind.

If not, there’s one more crucial step to success, and that brings us to our Bonus Tip:

You must gently wrap several of the longest leaves over the developing head to protect it from “blanching” in the sunlight that has sustained it for so long. Loosely join them with clothespins so you can still peer in to watch it reach the size indicated on that all-important seed packet.

Not losing a head to sunburn is the final hurdle, and then you’re home free… barring a sudden hard frost, or a late-season heatwave.

A close up of harvested cauliflower heads, tightly packed together with their leaves trimmed.

Once you’ve got your precious harvest, why not visit our sister site, Foodal for innovative cauliflower recipes?

It’s time to choose your favorite cauliflower varieties! Start planning for the season ahead. This year’s vegetable garden is sure to be your best yet.

Have you run into any hurdles while growing your own cauliflower at home? Share your stories, suggestions, and questions in the comments below. We love hearing from you!

If you found this article informative, you’re sure to enjoy:

© Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Uncredited photos: Shutterstock.

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!

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