Brassica Seed

Winter 2001-2002

By Nicolas Lindholm

Supported primarily through a grant from the Maine Dept. of Agriculture, this is the fourth in a series of five articles covering some of the most commonly produced and potentially profitable seed crops being grown by small-scale organic and biodynamic farmers in the Northeast. Nicolas Lindholm, co-founder and Executive Director of the Maine Seed Saving Network, studied almost 30 farms in New England and New York state, including large retail and small farm-based seed companies, market gardeners and family farms, CSAs, nonprofit groups, and a USDA farm that is part of our National Plant Germplasm System. Other articles in the series cover cucurbits, tomatoes, beans/peas, and lettuce.

Introduction and Overview

My study and these articles are meant to promote dialogue and develop interest in a niche market opportunity that a growing group of farmers and industry supporters has been quietly developing over the past 10 to 20 years: seed crop production on small farms in the Northeast. By this, I mean growing and marketing seeds of vegetable, herb and flower varieties for other farmers and gardeners to purchase, plant and grow, either directly marketed to the consumer or sold wholesale to regional seed companies. Current popular interests and trends, including preserving genetic diversity, growing and saving heirloom and open-pollinated varieties, organic gardening, and even anti-GMO concerns, have contributed recently to the rise of this largely untapped, potentially profitable niche market for small-scale, diversified organic farmers.

Most of the research and development efforts in organic seed crop growing and marketing to date has been done by the seed companies in the Northeast and by a few farmers, mostly in isolation from one another, each independently testing and overcoming production and marketing techniques and challenges. I believe that my study is the first economic viability study of seed growing for small farmers in the Northeast, and the first attempt to coordinate independent findings from these experienced growers and producers. The results are encouraging, at least for entrepreneurial farmers who are interested in exploring new markets and growing new kinds of crops, are able to remain diversified, and make sound marketing decisions based on economic analyses.

The Many Faces of the Brassica Family

Our culture uses many varieties and types of plants within the brassica family, from broccoli, cabbage, cauliflower and radishes, to old-time favorites such as turnip and rutabaga, to contemporary favorites such as arugula and many of the Asian greens that are common in mesclun mixes (such as tot soi and mizuna). This family of vegetables offers tremendous health and nutritional benefits to humans. Their popularity is further enhanced by the diversity with which they can be used in the kitchen and the relative ease with which they can be grown in the garden.

Known also as “cruciferous” or “cole crops,” the brassicas adapt well to our Northeast climate, as many are native to similar temperate climates (i.e., England, France, and parts of China and eastern Asia), where summers are not exceedingly hot or humid, and a moderate – not excessively cold – winter is typical. This makes them good candidates for seed crop production, as the need for season-extenders or other types of weather protection for the seed crop is minimal.

Seed of both annual and biennial brassicas is being produced and marketed by numerous growers in the Northeast, with both rewards and challenges. The favorable characteristics cited by growers who successfully save brassica seeds include the relatively large volume of seed typically produced by the plants within a relatively small space, the ease with which the mature seed is threshed from the dry pods, and, given proper selection of varieties, the adaptability to our climate for properly setting and maturing seed. What’s more, in today’s seed market, the availability of open-pollinated varieties of most brassicas is very limited (due to the heavy concentration of hybrid breeding programs), so growing quality seed of a quality open-pollinated brassica variety can be quite lucrative within a favorable supply and demand scenario.

Yet, brassicas are not the easiest crops to grow for seed. One of the greatest challenges is isolation, for brassicas cross freely within the same species, and even different species cross with each other to some extent. Insect pollinators are required to fertilize brassica flowers, which are for the most part self-incompatible, requiring pollen from another plant to achieve proper pollination.

A grower must know what species a given variety is and must properly isolate that seed crop from any other flowering brassicas within that species; to ensure complete purity, the variety should also be isolated from all other flowering brassicas, including wild mustards (a common field weed in the Northeast). Several methods of isolation exist, but the most economically viable is, as with other cross-pollinating crops, physical distance.

Most sources agree that a distance of one mile is required to ensure purity of a brassica variety. Therefore, only one seed crop of a given species is typically grown per year, and all adjacent fields and neighboring fields within a mile must be clean of any flowering brassicas. Note that isolation need only be from other flowering brassicas, not from vegetable crops harvested before any flowering occurs. (Most brassicas grown for vegetable use, such as cabbage, kale, cauliflower, turnip, radishes, etc., are harvested before they flower.) A seed grower needs only to look for wild mustard in weedy spots and brassica vegetable crops that can bolt or go by quickly, such as broccoli, radishes or hon tsai tai.

Another option, though not practiced by any current seed grower in the Northeast as far as I’m aware, is alternate-day caging. Here, two or more varieties can be grown near each other, but they must be enclosed within an insect-proof cage, made either of screen or of a row cover material like Reemay. On one day during flowering, one variety is uncaged or uncovered, and native insects pollinate these plants. That night, the variety is covered or caged again, and the next day, a different variety is uncovered. This alternating uncovering from day to day proceeds throughout the blooming period.

Caging can be used more efficiently and effectively on a larger scale by introducing your own bees into the cage for the blooming period. Here, the variety is never uncovered or uncaged, but is kept completely isolated within its own cage, and domesticated pollinators are brought into the cage and kept there for the duration of flowering.

Being strong outbreeding plants and largely self-incompatible, brassicas also require a population size that is generally larger than some of the easier seed crops. A good rule of thumb is to save seed from at least 100 plants for most brassicas, to maintain a healthy genetic diversity within a variety. Since winter-kill or other losses may occur within the two-year growing cycle, starting with 200 to 300 plants in the first year is not atypical.

This generally does not present a space problem for small-scale growers, as mature, flowering brassica plants typically need only about 2 square feet of space, similar to most cabbage, kale, or broccoli spacings. However, the mature plants are rather sprawling, with lots of thin branches, and do need to be staked and trellised to avoid physical damage from lodging or disease problems from lack of air flow through the plants.

One of the greatest challenges for seed growers in the Northeast is overwintering the biennials. To avoid a genetic drift toward a tendency for early bolting, a biennial seed crop needs to be grown in a full two-year cycle, where the first year the seed is planted and grown to a suitable sized plant that goes dormant over winter, then produces its flowers and seed pods in the second summer. A biennial brassica can be “tricked” into flowering and producing seed within a single year, but all sources and growers consulted agree that a two-year seed-to-seed growing method is best.

Problems inherent in this two-year system include the loss of plants to insects, disease, roguing, etc., and the loss of plants over the winter to various fungal, viral or bacterial problems, rodents, extreme cold, etc. Most brassicas need to be dug in the fall of the first year, stored in ideal conditions for the dormant winter months, then transplanted back into the field the second year. A grower must account for these labor and space costs (both in the field and in a root cellar or other controlled atmosphere storage room) to determine the economic viability of the crop.

These challenges are best overcome by selecting a proper planting and growing site (good drainage and tilth, balanced pH, proper nutrient levels – brassicas are heavy feeders) and selecting the proper crop and variety for the time and resources available. If no root cellar or storage area exists, then overwintering in place – in the ground – is an option for some crops. Kale is the best option here and is one of the crops of choice in my example below.

A biennial crop can be interplanted with some other cash crop (especially that first year) to subsidize the costs of the first-year growing. An early planting of lettuce either between plants or between rows of the brassicas is a good option. Some biennial brassicas can be sown or transplanted in mid- to late summer, perhaps after an early lettuce, spinach or other cash crop has been harvested.

Also, if part of the plant can be harvested before flowering, then the returns will be greater. Some small kale or tot soi leaves can be picked to add to a mesclun mix; one grower is experimenting with harvesting the whole head of a cabbage in the early fall, allowing some resprouting to occur before winter, then digging the plant. This may work because the whole head need not be on the plant (most of that will rot in storage anyway); only the crown is needed for survival and flower stalk and seed pod production in the second year.

A final challenge that all brassica seed growers face is protecting the seed and seed pods on mature, dried plants from excessive moisture and/or wind. Being dry-seeded crops, brassicas can be damaged irreversibly by rain if dry seed pods are exposed to long wet weather without a chance to dry out again quickly. What’s more, seed pod shattering is as big a problem around harvest time as is the disease pressure brought on by fall rains. Wind and continued drying weather can cause the seed pods to split and crack open, spilling the seeds onto the ground.

Timely and regular harvests are essential, especially as brassica seed matures unevenly upon the plant. Most growers will expect at least three separate harvests from a given brassica planting: first when the biggest branches are dry enough (before shattering), then when a large proportion of seed pods are ready, and then once or twice more when the last branches on the plants are ready. As with lettuce, the preferred method is to clip the plant using scissors or pruners, continue to dry the clipped branches inside under cover on a large sheet or tarp, then thresh them. Harvesting in the early morning with the dew still on the plants minimizes shattering the pods and spilling the mature seed.

For threshing and cleaning, many growers utilize simple hand tools at home, while others rely upon mechanical seed cleaners (such as a small, electric winnower with adjustable wind and screening capabilities – machines that some seed companies in the Northeast have and let their seed growers use). In either case, most experienced brassica seed growers make every effort to harvest quality seed pods and not get the seed too mixed up with chaff and dirt and weeds to begin with. Threshing can be quick and rustic by stamping, jumping, dancing or walking on the dried branches and pods on a large sheet or tarp. Brassica pods shatter very easily, so after most of the pods have been crushed and their seeds released, the bigger chaff can be gathered and lifted off by hand, then the smaller chaff can be screened and winnowed.

Given the above challenges, growers should experiment for a few years to discover what works best on their own farms. Incorporating brassica seed crops into a small-scale vegetable operation can certainly be economically viable.

Getting Seeds into the Soil

Table A shows both an annual brassica (bok choi) and a biennial brassica (kale) economic analysis. The example is neither a composite of the farms and growers I visited nor a case study of one particular grower, but a generic model for adaptation and study. A reader can look at this “budget” and say, “Well, I don’t have flea beetle problems, so I don’t need to use any row covers,” or, “I would need to overwinter the biennials using a different method,” or whatever variations might be evident on his or her own farm.

This hypothetical farm has 2 acres in vegetable production, managed by two full-time employees with some basic equipment, including a rototiller, hand tools, and a hoophouse. For the example, they use three 4′ x 100′ beds. Kale is grown in two of these beds from mid-July of the first year to September of the second year. Bok choi, an annual, is in the third bed from May till September of a single year.

Both crops are spaced 18″ apart in the row, two rows per bed, with the rows 30″ apart. This allows 132 plants per bed, an adequate population for bok choi and a generous amount for the two beds of kale.

In our example, bok choi is started in flats in the hoophouse in the early spring, then is transplanted into the growing bed by mid-spring. Like all brassicas, the crop will need high fertility, even moisture, proper weed control and pest protection to produce sizeable, healthy, prolific plants. These needs will vary from farm to farm. The same methods are used for the seed crop as for raising any brassica vegetable crop.

Kale, being a biennial, is grown differently from its annual cousin. Most sources and experienced growers cite better results by starting the crop in the summer, usually in July, rather than in the spring of the first year. This allows a cash crop, such as an early transplanting of lettuce, to be grown in the same beds from May till late June. Also, it eliminates having large, tall plants at the end of the first year; on the contrary, small plants produced from a July sowing are easier to mulch and have fewer setbacks from weather and pests as they overwinter. The plan is to keep the kale in the ground for the winter – not to have to dig it and re-plant it in the spring – a technique that is very successful with kale but is riskier with many other biennial brassicas in the Northeast.

Though many growers prefer to grow transplants, the farmers in our example direct seed this kale crop to save money (producing transplants is much more expensive than direct seeding). Also, direct seeding allows a much larger number of seeds to be sown, so an early roguing can be performed when the plants are thinned at about four to six weeks of age.

As with bok choi, kale requires specific cultural techniques to ensure a good crop, and our example provides for adequate weed, pest, fertility and soil moisture management. We know, for example, that a floating row cover like Reemay has proven invaluable for most brassica growers in the Northeast, so it is also frequently used for brassica seed production to protect against insect pests, both in the first and flowering years.

Once the first heavy frost has hit the small kale plants, usually in October, a heavy layer of clean oat straw mulch or other materials should be applied. Some growers have had success without mulch on overwintering kale, though many factors could spell disaster in this scenario – especially hungry deer and mice; a layer of chicken wire laid over a mulched bed will usually do the trick. Cold temperatures and freezing and thawing cycles usually cause some damage. Without mulch, a loss of even 50% of a planting could occur; with mulch, a loss of 10% to 25% may be expected. Our example allows for a loss of about 33% (starting with 264 kale plants and harvesting seed from 175) from winter-kill, wildlife damage, pest damage, and roguing.

Both kale and bok choi will have gangly, ranging branches of flowers and seed pods once they start maturing. A simple trellis should keep the plants from being knocked down by wind and rain and should help support the weakening plant stem and branches as they dry. The most common system is a stake and twine tie-up, similar to a basket-weave technique frequently used with tomatoes in a field, where stakes (in this case, short pieces of rebar or thin wooden stakes) are driven into the ground every 10′ to 12′, then a heavy twine (such as masonry twine) is tied from one post to the next, down both sides of the plants, holding the plants gently but securely within a brace of twine.

Any genetic tendency toward early bolting must be monitored. With crops like tomatoes or melons, particularly in a cool climate, plants that flower and set seed earliest are desirable, and a seed grower can select and save seed from the earliest ones to develop an earlier strain. With brassicas, however, selection should be away from early bolting. Some growers even rogue out the first bolting plants or, at least, any plants that diverge from the norm of the population as a whole.

Note that the farmers in our example purchase all of their inputs (soil mix, compost, straw mulch, etc.) as well as row covers and staking materials. Many of the growers I visited either produced their own compost, did not use row covers or mulch, cut their own wooden stakes (or did not stake at all. Thus, the bottom line of the Variable Costs column in Table A should be calculated for individual growers.

Growers should develop clear goals and plans with their intended buyer before a brassica seed crop is started. When wholesaling to seed companies, you must have a variety that they know will be in high demand. Either the farmer or the seed company should trial and assess each variety prior to initiating commercial seed crop production to become familiar with the plant and to determine a balance and selection of varieties that work. Low-yielding, less popular or otherwise challenging varieties can be grown successfully if, in advance, the grower has arranged for price premiums or selected other high-yielding or more profitable varieties to “subsidize” the other.

Table A

Looking at the Numbers

I have used three sets of figures for both bok choi and kale to represent a range of yields that reflects growers’ experience and harvest data gathered in this study. As with most vegetable seed crops, yield and wholesale prices for seed vary among varieties and species, so the tables show a range of possibilities.

Table B shows a simple cost/benefit analysis for our brassica seed crops. The fixed and variable costs of our hypothetical farm (Table A) for bok choi and kale are added together respectively to determine the total cost of production for each crop. Individual costs per square foot and per plant are then proportionately made. The expected income can then be compared using the three different yield figures and a typical, current wholesale price. The benefit tables then show the total gross sales, the gross sales per square foot, and the gross sales per plant for each of these possible yields. These sales are based on a current wholesale price of $65.00/lb. for both bok choi and kale seed, a price that is near median, though some seed companies do pay more or less, and some varieties can be worth more or less.

Table B

The yield-to-sales relationships in the cost/benefit analysis help define what can or cannot be profitable. The net income (the last three columns in the benefit tables) is calculated by subtracting the respective costs from the gross sales.

For bok choi, a low yield of .02 lbs. of seed per plant (about 1/3 oz. per plant or 2.6 lbs. per 132 plants) results in a total loss of $89.14. For good yields of .03 lbs. per plant (about 1/2 oz., or 4 lbs. of seed per 132 plants), we nearly break even at $1.86 net (which can still be viewed favorably, for the costs covered here include all fixed and variable costs, including labor). Yields close to .05 lbs. per plant (about 3/4 oz., or about 6.6 lbs. per 132 plants) are most profitable under this model, as gross sales are well above costs, resulting in a $170.86 net.

For kale, the lowest yield figure generates gross sales that fall below the total costs, while the highest yield figure demonstrates a highly profitable net return. In the middle, a moderate yield of .06 lbs. per plant (about 1 oz. per plant, or 10.5 lbs. of seed per 175 plants) covers all costs, with a $47.59 net.

Table C shows a simple break-even analysis, which is used to produce two separate calculations: first, a selling price (at the given yields and costs) at which the grower will “break even” (i.e., cover costs but not make a profit; then, the quantity needed to be sold at a given price (in relation to the costs) to break even. Higher selling prices or yields result in a profit.

Table C

The break-even selling price calculations for bok choi show that a yield of .03 lbs. per plant is near the break-even point for the “average” wholesale price of $65.00/lb., as the calculated selling price is $64.54. A slightly lower yield of .02 lbs. per plant would be unprofitable if the wholesale price is $65.00/lb.; however, if the grower can negotiate or attain a wholesale price of $99.28/lb. or higher, then the crop will break even or be profitable at this yield. For a good yield of .05 lbs. per plant, the calculated break-even selling price is well below the average wholesale price, indicating certain potential for profit. Our best scenario, with .05 lbs. of seed per plant, breaking even at $39.11/lb., can provide a $25.89/lb. profit if sold at $65.00/pound.

Likewise, with kale, our low yield of .05 lbs. requires a selling price of $72.56 to break even, while yields of .06 lbs. and .08 lbs. of seed per plant can provide moderate to excellent profits for the farm if sold at $65.00/pound. Note that these calculations can and should be used to determine or negotiate any appropriate selling price, higher or lower than the average, whichever may be required or desired by the grower and/or the buyer.

Our final analysis, the break-even quantity sold, suggests a range of profitable models based on three selling prices. The current average wholesale price for bok choi and kale seed ($65.00/lb.) makes modest yields of about .03 lbs. of seed per bok choi plant and .056 lbs. of seed per kale plant economically viable. These yields are well within the range of experience and data collected in this study. Prices as high as $75.00/lb. can allow a grower to break even at lower yields per plant (.026 lbs. for bok choi and .049 lbs. for kale), and yields above these figures should be quite profitable. In the other direction, prices as low as $55.00/lb. will require a yield of at least .036 lbs. per bok choi plant and .066 lbs. per kale plant to break even.


Seed for open-pollinated varieties of broccoli, cabbage, kale, and other brassicas is in demand. Entrepreneurial farmers in the Northeast can use this opportunity to open new markets, further diversify their family farms, and remain economically viable.

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