Broccoli plants want around 15-18" diameter of soil to themselves. If you're doing
container gardening like I am then this means you probably won't be growing many
plants. Mine were Waltham broccoli.
2008 crop - Waltham Broccoli, seeds certified by Ecocert Canada
Broccoli germination (see photos below) happens like a lot of other plants. Plant the
seeds about 1/4-1/2" deep in soil but place the soil lightly over the seeds. You want
the seeds to be able to get air. I kept the soil warm by putting it on a south facing
window sill and moving it to an inside shelf during the night. I also kept it
wet but not overwatered. I was pessimistic and planted too many seeds
close together. They all
germinated and I ended up separating them
soon after the photos below into their own small containers and gave all but
two away. I started my seeds at the beginning of April thinking I'd transplant
them at the end of April but realized that it was the end of May that I
wanted to transplant them. So middle to late April would have been
good enough to start the seeds.
I transplanted the broccoli to a large outdoor bin around May 31 (in Ottawa,
Ontario, Canada.) The above plants were about 8 to 10" tall by then.
Over the next few months, as the photos below show, there were a lot of leaves
for weeks, so many for so long that I began to wonder if I'd get any broccoli.
This was while the temperature was always 22C or more. Finally at the beginning of August
we had two weeks in a row where the temperature
was a little cooler during the days and at night went below 20C. It was during those
two weeks that the broccoli first appeared and grew rapidly all the way to what you see below.
So the next time I grow broccoli I'll start them closer to the fall so I don't waste
so much time and nutrients growing leaves.
About a week after cutting the above broccoli from the plant, side shoots started
growing broccoli too (see the photo below.) The side shoot broccolis are smaller
as you can see, but they add up. After you cut those off, more should grow
lower down but that was it for mine.