Published in Spring 2022
By: Heidi Noordijk, Small Farms Program, Oregon State University
Spring time brings freshly harvested purple sprouting broccoli and cauliflower to market booths and CSA shares throughout Western Oregon. The current climactic conditions of the Willamette Valley are suitable for overwintering cauliflower and purple sprouting broccoli production. Much of the knowledge on production of these crops comes from the UK, Coastal France, Spain, and Italy which are known for these winter crops. OSU Extension and the Organic Seed
Alliance have been doing trials for suitably of these crops in the Pacific Northwest. Overwintering cauliflower and purple sprouting broccoli require less irrigation during their production cycle than fall maturing varieties, create more opportunities for farms to retain year-round employees, and have high market demand from consumers looking for fresh local produce from late winter through spring.
Inspired by the increase in production and demand for winter vegetables, variety demonstrations for overwintering cauliflower and purple sprouting broccoli began in 2015 at OSU’s North Willamette Research and Extension Center (NWREC) in Aurora, Oregon. Outcomes from these demonstrations and information from experienced winter vegetable farmers and plant breeders will be shared in this article.
Crop planning and growth responses to temperature
Experienced farmers, researchers, seed breeders, seed distributors, market managers, and wholesale distributors were consulted on crop planning, field management, and variety selection. The first year of the demonstrations looked at potential planting dates for production in the North Willamette Valley. Both overwintering cauliflower and purple sprouting broccoli had plant spacings of 18 inches in row and 24 inches between row. Planting dates of August 18, September 1, September 16 and September 30 were selected with the goal of having a plant that is 2/3-3/4 full vegetative size going into winter. Planting too early can lead to large, lush plants that are more susceptible to disease and cold injury and planting too late leads to small plants that won’t form viable heads and curds. Plants from the September 16 and 30 planting dates were too small going into winter and did not produce a marketable crop. In 2018 the project continued with planting dates of August 7, 17, and 28. The best results were from the August 7 and 17 dates. Mid-August was selected as a transplant date that worked for Aurora, Oregon and was used for the 2019-2021 plantings. Farmers throughout the Willamette Valley transplant in the fields between mid-July and mid-August, with greenhouse seeding occurring four weeks earlier.
Cauliflower goes through several growth stages before developing a marketable curd, three of the stages are: juvenile, curd initiation, and curd growth. The juvenile stage is when leaves are developed and the framework of the plant is formed, this stage ends when the plant has developed a certain number of leaves and has met a temperature requirement to begin curd and head initiation. In cauliflower this can range from 32 and 112 leaves, depending on variety and seasonal weather conditions. Curd and head initiation of cauliflower and purple sprouting broccoli is triggered by vernalization, a response to prolonged cold temperatures. Once the chilling requirement is satisfied, the curd and head can begin to grow and expand. Without receiving these cold temperatures viable curds and heads will not form.
Temperatures that are too cold can damage the plants. Most of the common winter cauliflower varieties are hardy to about 19°F and hybrids have survived temperatures of 10°F. NWREC is currently in USDA Plant Hardiness Zone 8b with low temperatures expected between 15-20°F. All varieties are transplanted on or around the same day, however their harvest times will vary depending on their cold requirements and seasonal temperatures. Breeders have modified overwintering cauliflower so they will form curds with varying degrees of cold requirement. When crop planning, select varieties that work with your market and CSA needs, some farmers will have an early, mid, and late variety for each crop. If weather is warm during the growth period, some of the varieties may have overlapping harvest windows. Changes in weather can lead to differences in harvest times from year to year.
Nutrient management and irrigation
The recommended soil pH for Brassicas is 6.3, if there’s a history of clubroot in the field a pH above 6.5 can be helpful. Take a soil sample of your fields before planting, use those results and follow guidelines from OSU Extension’s publication on Nutrient Management for Sustainable Vegetable Cropping Systems in Western Oregon to create a plan. Boron deficiency can lead to hollow stems in cauliflower and broccoli, boron can be applied as a preplant application or with split foliar applications starting around 4 true leaves. A soil nitrate-N test taken a week or two before planting will help in calculating the nitrogen needs to establish the crop. The NWREC demonstration plantings aimed for preplant N levels of 50 lb/A. Excess nitrate will leach with the fall and winter rains, so don’t apply more than necessary. Dale Hemphill, a former vegetable researcher at NWREC conducted overwintering cauliflower trials in the late 1970’s and early 1980’s. Hemphill noted that “winter cauliflower has consistently responded to spring nitrogen application with increased yield, greater head size, and better foliage cover of the curd. Greatest yields have been obtained with side dress application of 100 lb/A of N in early February and again in early March”. The 2020/21 trials at NWREC received one side-dressing of feather meal at a rate of 50 lb/A of N in early March for the later maturing cauliflower varieties. The purple sprouting broccoli demonstrations at NWREC were not side-dressed. Experienced winter vegetable farmers with high levels of soil organic matter do not side-dress their cauliflower or purple sprouting broccoli and have been satisfied with the results. More research could be done on nutrient management of overwintering Brassicas in the Willamette Valley. Transplanting occurs in mid-July to mid-August, often hot and dry conditions in the Willamette Valley, pre-irrigation and supplemental irrigation for plant establishment are needed until fall rains arrive.
Results from 2019-21 variety demonstrations
OSU Metro Small Farms Program partnered with the OSU Vegetable Program and the Culinary Breeding Network in 2019 on a project to promote awareness and consumption of winter vegetables in Oregon. Included in this project were community outreach events, fields days, development of a project website for farmers and market managers, and overwintering cauliflower and purple sprouting broccoli variety demonstrations at NWREC. Varieties were selected using results from past NWREC trials and recommendations from farmers and seed companies. Most varieties had two replicated plots each year and results are summarized in the
graphs and tables below.
Challenges
Producing overwintering vegetables can be challenging and hurdles can change from year to year. Late July to mid-August is a busy time on many farms, having enough time and a large enough crew to transplant winter vegetables while in peak summer harvest has been a struggle for growers. Unpredictable weather with extreme heat events, ice storms, and frosts can impact survival and development of these crops. There are few seed companies that offer overwintering cauliflower for the PNW, consistent availability of varieties has been a challenge for growers in the region. Geese have destroyed fields of overwintering purple sprouting broccoli and rodents (voles and field mice) have also damaged this crop. Pests haven’t caused too many problems in these winter crops. Aphids, cabbage looper, diamond back moth, and imported cabbage worm can cause slight damage to young plants. Slugs and cabbage maggot have made cauliflower curds unmarketable in spring. Brassica crops are grown in all seasons in the PNW, having enough ground for rotations to avoid disease and insect pests can be an issue.
Farmer advice and resources
Experienced winter vegetable farmers shared guidance throughout the NWREC variety demonstrations and they’ve provided advice for farmers thinking about adding winter vegetable production to their farms.
• Know your market and why you want to do this. Do your customers want winter vegetables? Do you have enough acreage? Do you have the labor? When you plant these there are lots of other things to do on the farm in July and August. Do you have enough labor to handle this?
• Winter vegetables make sense for direct market growers at the small to mid-size farm range, but you need to be careful. Cashflow and retention of customers and crew is good, but it is challenging and really hard. Winter vegetables fall mid-range in terms of profitability
• Dealing with the wet and muddy fields slows down harvest, to help alleviate muddy conditions in the field interseed cover crops in September to provide a cover in the pathways so the field doesn’t become a mud bog
• Some varieties are difficult to get a hold of because winter vegetables are a niche product for seed companies. Work closely with your seed companies to select varieties that fit your needs. Look for hardy, tasty, and productive varieties.
• There’s nothing like seeing purple sprouting broccoli or winter cauliflower reach maturity in late winter or early spring after all you’ve had for a while is leafy greens and root vegetables
• Visit the Eat Winter Vegetables website: https://www.eatwintervegetables.com for recipes, cooking videos, and variety information. Share this resource with your customers.
• Check out Purple Sprouting Broccoli: A Guide to Growing for Fresh Market and Seed in the Pacific Northwest from Organic Seed Alliance that was published in November of 2021.
• Reach out to Heidi Noordijk if you’re interested in joining a winter vegetable farmer network.