Being in zone 9 makes growing cool weather crops a bit of a challenge, especially if you are trying to follow the instructions usually given on seed packets. I finally gave up and used science as my guide. What do you know, it worked.
Most planting guides will tell you to grow crops like broccoli starting in February or March, but by then it’s really too late. Sudden warm streaks, or sooner than expected summer temperatures tell the plant to bolt (go to seed), and you wind up with spindly heads, if any at all. However, broccoli doesn’t start well in cold temperatures so trying to get an earlier start doesn’t work well, either.
A handy growing summary chart is at the end of the article.
My breakthrough came in the form of a seed catalog that showed the best germinating temperatures for various seeds. It turns out broccoli likes warm soil to start (about 70-80 F), then cool temperatures to mature. That means starting them at the end of summer or early fall for an early winter harvest. If you want a spring crop you could plant in mid-fall and let them overwinter to mature in spring, or start indoors in pots in mid-winter and transplant once they are about 3-4 inches tall.
Of course, there is always the option of buying pre-started plants, but they are not always available in the summer for a fall harvest. You will typically see them in late winter for a spring crop. Be sure to get them in the ground by mid-February in warm climates, otherwise they will get caught by the heat and you will have lost your chance!
I like to put 2-3 seeds per hole, and space holes about 18 inches apart on all sides. The holes should be no more than 1/2 inch deep. Once the seedlings emerge and are about 1 inch tall, thin them by pinching out all but the strongest plant from each hole. Don’t pull them because the roots from all seedlings will be tangled and you could rip them all by accident. I have been pretty successful at digging up all the seedlings from each hole and GENTLY teasing apart the roots in order to use the extras to fill in spaces where seedlings didn’t emerge or got nibbled by other critters. It requires being very gentle and very patient to make it work!
Pests to watch out for are snails/slugs, cabbage moth larvae, and sometimes even pill-bugs will go after the stems of seedlings. Watch out for birds, too! My poor plants got nibbled until I protected them by putting strawberry baskets over the seedling to keep the birds away.
Broccoli prefers evenly moist soil and full sun. The soil should also drain well and will have the best production if there is a good nutrient balance. A good layer of compost will help greatly for both quantity of flower heads as well as taste.
Harvest your heads when the little florets are just starting to loosen, but before they open up. If you miss that window and you start to see tiny yellow flowers appearing, no problem, they are still good, but get to them right away. Don’t be too quick to cut off the heads, though, as you may get them before they reach their best size. Cut them with a sharp pair of scissors at the base of the central head, but watch out for any side shoots that may be forming. Be sure to leave those on the plant, as they will also start to fill out. They are typically not as big, but they will be just as tasty. In fact, some varieties of broccoli are known for producing a lot of side shoots which extends your harvest well through the season.
Broccoli can take light freezes with no problems and still continue to produce. I had one that had been planted in late summer that kept producing side shoots all throughout the winter. However it’s preferred range is above 40 and below 80 F. Once temperatures start getting hot, it’s time to pull out the plant. The heads will start getting spindly and won’t taste good if formed during hot weather. If you have not had soil problems you can put your old plants into compost. Otherwise put the roots in your green waste garbage and the tops can be composted.
- Height: up to 2-3 feet, depending on the variety
- Width: up to 2-3 feet, depending on the variety
- Sun: full sun, or part shade in warm weather
- Water: keep soil moist, but not soggy
- Soil pH: 6.5 – 7.5
- Soil type: loose, amend with organic material if soil is either very sandy or heavy clay
- Key nutrients: balanced, preferably suited for flowers since that’s what broccoli heads really are
- Planting time: zones 8+ in early fall or early spring