Broccoli is categorized as a cool-season crop, and the best-flavored broccoli forms heads during mild weather. In our Napa Valley climate, we have two prime times to grow it in home gardens: early spring and fall/winter.
With that in mind, the field-testing group of the Napa County Master Gardeners decided to grow broccoli twice: in the fall of 2021 and again in the spring of 2022.
I like broccoli. I consider it a staple of my winter vegetable patch. My favorite varieties produce a large head at the beginning of the season, and then produce smaller side shoots over the next two or three months (or even longer). I jumped at the chance to trial it with other growers.
Location and preparation of the planting area is important. All vegetables need plenty of sunlight to produce a crop, and fall-planted broccoli in particular needs to be in full sun for optimum growth.
Master Gardeners who planted in shadier locations reported much slower growth than other growers. These plants are also considered heavy feeders, so amend your garden soil with compost and add fertilizer formulated for vegetables.
Broccoli is typically grown from young seedlings transplanted into the garden. These starts are usually available from local nurseries in February or March and again in September and October.
For our fall trial, we agreed to start seeds in August. It takes about six weeks under good growing conditions to get an optimally sized transplant. Planting transplants in the first half of September allowed about two months of growing time before the short and cold days of winter slowed them down.
August heat can be challenging for cool-season crops. Although warm days facilitate seed sprouting, baby broccoli plants do not like temperatures above 90F. With careful attention to watering and keeping plants shaded in extreme weather, we were able to get decent transplants.
We chose three varieties that seed catalogs said would produce multiple side shoots after the main head was harvested. These were Apollo F1 sprouting broccoli, De Cicco Crown Italian heirloom broccoli, and Marathon F1. We should have looked more closely at the descriptions, as it turned out that “sprouting” broccoli doesn't form much of a central head, and the heirloom Italian broccoli formed small heads.
Our fall-planted broccoli produced small amounts of edible shoots starting in mid-November, but significant production began in January. Once main heads were harvested, all types produced edible shoots into April.
Our spring growing trial commenced with starting seeds in January. Again, you need at least six weeks to go from seed to transplant, and broccoli seed started in mid-January was ready to set out in March.
Weather was less of an issue for these starts, as broccoli plants do not mind cold weather. Some growers started seed using heat mats which resulted in sprouts in three to four days. However, everyone had sprouts within a week or 10 days.
Transplants set out in March started producing edible shoots and heads in May. Just like the fall trials, multiple side shoots followed. It is worth noting that the broccoli harvested during July and August had a stronger taste than broccoli that matured when it was cool.
Broccoli is not entirely trouble-free for home gardeners. Many of the Master Gardeners use row cover or other physical barriers to keep flying pests off the plants. Besides deterring birds, which like to eat the leaves, row cover protects from the imported cabbage worm (the larvae of a small white butterfly) and cabbage loopers (larvae of a small brown moth). Both of these green caterpillars are the exact same shade of the leaves they eat and can skeletonize leaves in short order.
In some gardens and at some times of the year, especially spring, aphids can be problematic. Monitor plants closely so you can take action before the aphids multiply.
If gophers are active in your garden, they will love your broccoli. Grow in gopher-proof baskets, containers or raised beds.
Every participant in the broccoli trials confronted at least one of these pests. For addressing these pests and others, we highly recommend integrated pest management practices.
At the trials' conclusion, participants had different favorites. Some really liked Apollo F1 Sprouting with its slender, tender stalks. Others preferred the more traditional Marathon F1 broccoli. De Cicco Crown was somewhere in the middle in size.
While we didn't settle on a favorite variety, we can assure you that broccoli grows well in Napa Valley. In our mild climate, if you plot the planting times correctly, you can harvest broccoli most of the year. Of course, you might have to contend with pushback from the rest of your household. One spouse of a participant reportedly asked, “Do we have to eat broccoli every night?”
Workshop: Join UC Master Gardeners of Napa County for a workshop on “Garden - Garden Ergonomics: Using the Right Tool the Right Way,” on Saturday, January 28, from 10 am to noon, at Las Flores Community Center, 4300 Linda Vista Avenue, Napa. Learn proper body mechanics and how to avoid common gardening habits or activities that are risk factories for injury.
Library Talk: Join UC Master Gardeners of Napa County and Napa County Library for a free talk on “Love Your Rose Garden” on Thursday, February 2, from 7 pm to 8 pm via Zoom. Learn more about finding the right rose for your garden, planting roses and basic care. Register at https://ucanr.edu/2023FebRosesLibraryTalk
Food Growing Forum: Join UC Master Gardeners of Napa County for a seminar on “Winter Seed Starting and Planning” on Sunday, February 12, from 3 pm to 4 pm via Zoom. Learn about selecting spring seeds, seasonal timelines for crops, succession planting, soil preparation, special supplies and tips for success. Register to receive the Zoom link: http://ucanr.edu/2023FoodForumFeb
Help Desk: The Master Gardener Help Desk is available to answer your garden questions on Mondays and Fridays from 10 a.m. until 1 p.m. Send your questions to firstname.lastname@example.org. Include your name, address, phone number and a brief description of the problem. For best results, attach a photo of the plant. You may also leave a voicemail message with the same information at 707-253-4143.