At least for me, onthe roof.
The Problem with brocolli, is that it is a cool season crop, but it takes a fairly long time to mature. Last year I put my transplants into their raised beds in early to mid April. The seemed to grow fast, big, and hardy. But by late June or early July when they began to develop their heads, the temperature of the soil was often above 80 degrees. I tried to cool things down with shade-cloth, but the ambient temperature of the roof (it was a hot June, too) overwhelmed any coolness the soil might have retained. On the roof, the soil will be the same temperature as the air, or warmer, as the roof surface can go well into the 100’s–hot enough to burn skin.
I am devoted to brocolli. When my wife and I used to get our veggies primarily from the grocery store, we ate brocolli almost every night. One way or another, I determined, I would grow good roof-top brocolli. So I started my seeds inside in mid-January, and planted good sized seedlings in the middle of February. This brocolli would not suffer from over-heating.
About two weeks ago the first tight heads began to form and grew steadily larger and fuller. But about a week ago something else happened. Instead of growing large and tight, the earliest ones began to open and spread. They was about to flower, even though the soil temperature dips into the 50s at night, rising to the 70’s, only, during the day. Perfect brocolli growing temperatures. What happened?
Apparently prolonged exposure to cold weather can cause brocolli to flower prematurely, to create “buttons.” While still tasty, unlike the heat-caused bolting, these were paltry looking little sprouts–the brassilica version of Charlie Brown’s Christmast tree. I included them in the CSA boxes this week. I hope my subscribers remember the experimental nature of my project as they nibble on these gangly little guys.
The good news is there is another round of brocolli, about 2 or 3 weeks behind this one, just starting to form its heads. They look tight. They didn’t suffer the cold nights of February. Perhaps they will grow large and tight.