Growing Cauliflower in a Greenhouse: Perfect Conditions All Year Round


Another Reason to Love the Greenhouse: Perfect Cauliflower Growth

Lennie tracked me down at a party. “It’s my cauliflowers,” she sighed. “They are small and button-like instead of big like at the store.”


Donna's Grandkids Mali, Kale and Cohen with greenhouse grown cauliflower- it's a big one

Donna's grandkids Mali, Kale and Cohen with greenhouse grown cauliflower

Cauliflower: The Wonder Food

The popularity of cauliflower is skyrocketing. It is called the new wonder food and whole books are being written about cooking cauliflower. Meanwhile, the cost of organically raised cauliflower at the market this week is approaching $10 per head. It’s fair to say global interest in cauliflower is bigger than ever and Lennie is on-trend and trying to grow it.

Why Cauliflower is More Challenging to Grow Outside

And I am right there with her - nodding and sympathetic – “It’s the weather outdoors”, I tell her “the same thing is happening to my outdoor cauliflowers this year.”

I usually grow beautiful heads of cauliflower outdoors and last summer I even won the top prize at the local fair with my green Susanna cauliflower.

But this year, in our area, it got too hot too fast and this tricked the plants into maturing early. So they went from seedlings to flowering plants almost overnight. (p.s. the flower on cauliflower starts as the “head” we normally eat.) When heads form and start to open up while the plant is still small they won’t get any bigger. You’ll need to pick them at once and probably need to eat your whole crop in one sitting to get enough for the family. And then what will you do for the rest of the summer?

Greenhouse Growing Conditions for Perfect Cauliflower


Luckily Lennie’s story reminds me of another reason I love my Greenhouse Garden The climate. And by this I don’t mean just climate extension: we expect earlier springs and longer falls in a greenhouse. But it’s the ongoing steady greenhouse climate that promotes perfect cauliflower growth because of the even growing conditions.

In a covered growing area you can get A+++ cauliflower. Steady temperature, even light levels, evenly moist soil and steady nutrient supply because the weather inside your greenhouse is always perfect!

In my greenhouse, I started cauliflower seeds on February 22 and planted them in the ground inside the greenhouse on March 20. I planted the extra seedlings outdoors in April once the weather was settled but still cool at night because cauliflowers tolerate frost.

In my Northern latitude, it takes about four months from seeding to harvesting cauliflower in my greenhouse so I have already picked my first cauliflower crop this year and it is so sweet and tasty it is hard to believe it is a vegetable.

The Perfect Timing to Plant Cauliflower in a Greenhouse


Outdoors, my cauliflower takes about five months from seed started in my greenhouse and transplanted outdoors. In southern growing zones and inside my modestly heated greenhouse, the fall crop of cauliflower will be planted in later summer and into early fall.  I am watching daily to see when the seeds, just planted, will emerge. It has only been four days since seeding and the first seeds are through the soil. I will let them grow until they get 4-6 leaves and then plant them by mid to late July in my greenhouse beds as I remove my larger zucchini plants. (I do this every year: once my outdoor zucchinis are producing well enough I pull the zucchinis growing in my greenhouse out of the ground and compost them because they are no longer needed.) From the plants I seeded this week, I will harvest beautiful heads of cauliflower in my greenhouse from November into January.

Cauliflowers tolerate frost so in Northern climates they are planted outside in spring before any of the more tender plants like tomatoes are planted. Then a second crop is started in May and finally, a third crop is started as time and space allow. This third crop, the fall crop, needs the steady conditions a greenhouse offers.

Warning! Last July I discovered a flaw in my system. No single-family can eat twenty cauliflowers all in the same week. So this year I am being careful. In spring I only seeded eight cauliflowers at once: four in the greenhouse and four outside. Each cauliflower can grow to four feet (1.25 metres) across if space allows.  Planting closer will also trigger smaller heads.

Cauliflower Crop Planning and Tips for Greenhouse Growing

In the greenhouse, I use a drip irrigation system to keep the soil evenly moist.  I provide a gentle breeze from an overhead fan and I shade the greenhouse in summer with overhead fabric (see last month’s article about shade cloth.) Before I plant anything in the soil I amend it to make sure minerals are at the perfect level (using the Complete Organic fertilizer recipe on page 84 of Steve Solomon’s book The Intelligent Gardener).

Conditions are perfect indoors and my greenhouse cauliflowers are gorgeous. But like Lennie, I failed outdoors this year. All four spring-seeded heads matured early and made tiny heads barely worth steaming. If there is one thing I know it is this: do not take a holiday or even a weekend away if you are manually managing cauliflowers outdoors. They need even moisture, light shade and consistent temperatures. A heatwave or holiday-induced dry spell means disaster.

So I quietly pat Lennie on the shoulder and tell her to try again. In a greenhouse, seeds planted this week will surely mature by late November. And with any luck, she can order a greenhouse for fall delivery – just in time to install her fourth crop, the overwintering cauliflowers.

For more information about cauliflower varieties worth trying, check out

Flame star cauliflower had so much potential.... but the colour was pale yellow once cooked and not as pretty

Flame star cauliflower had so much potential.... but the color was pale yellow once cooked and not as pretty.

So many kinds of cauliflower seed are available - play around a bit in your greenhouse!

So many kinds of cauliflower seed are available - play around a bit in your greenhouse!

Past prime

Cauliflower Past Prime: once the head starts to get loose or "rice" it is past its prime. I still eat them like this anyway, but it would never be sold this way.


More From Donna

For more great tips from Donna, visit

You can also read Donna’s gardening books: No Guff Vegetable Gardening with Steven Biggs and her just-released Gardener’s Gratitude Journal:  Part Diary, Part Personal Growing Guide.

Donna Balzer