Lettuce Brassia Production

Lettuce and Brassica Seed Production (notes)
Organic Seed Alliance field day, July 19th, Philomath, OR.

These notes are a record of some of the information shared at Gathering Together Farm, where the field day focussed on seed production by Frank Morton, a specialty lettuce and brassica seed producer, and farmer-breeder.

by Patrick Steiner

Frank Morton’s philosophy and approach to seedgrowing. In the early 1980’s Frank was a mixed salad grower; started growing seed for lettuces and other salad greens for self-sufficiency – many not available except in Italian catalogues. Chance crosses produced expansion of diversity in his garden, which he used in his salads. Eventually the growing out of these crosses led to unique new salad greens that people asked for, and his seed company was born.

Maintains that growing seed for own use can be very beneficial for a farmer. Your own seed will quickly adapt to your farm micro-environment, giving you faster germinating, more vigorous plants. Claims that within 3 seasons you will see a performance difference between your seed and identical cultivar of commercial seed. Additionally, it is important to grow seed for the varieties important to us so that we have it when these varieties are dropped, or only available as treated seed, etc.

Frank strives to see small, organic farmers grow organic seed, not to see organic seed grown by previously conventional growers who have decided to pursue a market niche. Debunks myth that large companies grow good quality seed and small organic growers are hokey – reminds us that conventional seed companies not always keeping seed perfectly disease free, or free from off-types, etc. Example: Frank grew out a hybrid pepper to begin stabilizing it as an o.p. Out of 50 plants growing, only 4 were what he considered ideally uniform. Summary – we can grow seeds for plants that are as high quality a conventional seed, even better if we are growing for our own needs which we know best.

Variety trialling

The first stage of any breeding project, or even of just growing out a vegetable variety for seed production is screening the germplasm. This simply means growing out several cultivars, or several lines of a specific cultivar in order to observe differences and see strengths and weaknesses of each line. By investing a season in doing this you can then go on to grow seed of a particular variety or line, confident that you are starting with the best variety or genetic material you can find.

Once you have identified a line/cultivar or selection of a particular variety that you like, this becomes your stock seed, from which you do all growouts for seed. You may do several generations of growing out seed from this stock seed, using the resulting harvest mainly for vegetative growouts, ie sale as fresh market produce. Always go back to your stock seed for seed growouts, because this is a known quantity. This is important because a variety is not a static thing. Even in self-pollinating plants there is a gradual accumulation of variation that over time will make the variety much different from what you started with. You can do selections on your stock seed, thus improving it, and replace your old stock seed with this new selection. This new selection will now be your stock seed.

Selection for desired characteristics – both in vegetative and reproductive stages

You can select from one plant for desired characteristics through “spacial selection”. This involves harvesting seed from specific areas of the plant, to isolate different traits. For example, in brassicas to select for latest bolting characteristics you select seedpods from the lower branches of the plant, and even more specifically from the tips of those branches. These seedpods will have formed from some of the latest flowers in your plants and will include genetic material that has “self-selected” for late bolting.

While making selections or rogueing your plants to improve your final lot, you can do selection at different stages of the plant’s growth. You can make selections that effect the vegetative form of the plant during that phase of its growth. For example, select for single centers in romaine lettuce during the late stage of it’s vegetative growth, when heads are filling out. You can make selections for the reproductive stage of a plant during that phase of its life. Experienced growers will note that some lettuces produce straggling, or trailing seedstalks that fall to the ground. Other lettuces have multiple side shoots with seedstalks. No amount of selection at this stage will improve the characteristics of the plant in it’s vegetative stage, but you can improve the plants in their reproductive stage. For example in lettuce select for straight, upright seedstalks that make harvesting easier and minimizes chances of seed loss.

Sometimes our selection for desired characteristics can have unforeseen consequences. For example, usually we think it is a good idea to select the last bolting lettuces in order to get seed from plants that have “bolt resistance”. However, Frank experienced problems with late-bolting romaine lettuce. Those heads, because they stayed in their tightly wrapped leaves for longer before bolting then got botrytis (a fungal disease that causes rotting). While in Frank’s field we saw this, and other plant breeders present suggested stripping the leaves from the bottom stalk of the plant in order to expose the grey mold to air flow and let it dry out. If the weather is dry Franks’ lettuce should be able to survive the botrytis attack.

Planting and timing

Timing for planting of seed or vegetative crops can be quite different. For example with cabbages the technique is to plant seed cabbage late in the season. One strives to get the plant to a stage in its life where it is a large-leaved rosette at wintertime, but without the head having yet formed. The plant thus survives the winter nicely in the ground, with no blanched leaves in the cabbage head to freeze out. In the spring, flower shoots readily come out of the plant and form seed. It is important to have grown the seed lot to maturity previously and ascertained if the heads from this seed are uniform and do not require much selection. Also, this technique for cabbage seed production may only work in areas where there are mild winters, such as BC’s coast.

Harvest techniques – Lettuce

Frank has developed a unique harvest method for lettuce seed that is efficient and economical. Frank watches his lettuce begin to flower, and waits until the first seeds are dried down on the plant, almost about to fall off. At this point he harvests the entire plant, including the root ball. Carrying them from the field he lays the plants out on long rows of landscape fabric, also called geotextile fabric. This fabric is also used for underlay on asphalt roads and can be found at hardware stores or through contractor supply outlets. It is more durable than remay/floating row cover, and still allows rain or moisture to pass through, unlike plastic tarps which can pool water that will ruin seedheads. He is careful to place the rootball on the ground (off the fabric) with the seedheads lying in the middle of the fabric. Two rows of lettuce can be placed on the fabric this way, both with heads toward the centre of the strip, rootballs off the end of the fabric. The fabric is commercially bought for approximately $100 for a 300 foot length that is 5 feet wide. The fabric allows moisture and rain to go through, but not seeds, so plants can be left to further dry in the field for several days after harvest. This is critical since not all the seeds have fully matured or dried down at harvest time, but will slowly do so over the course of a week or so on the fabric. This is why Frank harvests the lettuce with rootball intact, to encourage continued growth of the seeds.


Once the seed has matured and dried, Frank moves the plants onto a plastic tarp, still making sure the rootball is not on the tarp. At this point he can beat the plants with a stick, effectively threshing the seed from the plant. After removing the threshed seedstalks he has a tarp full of seeds, lettuce chaffe, leaves and aphids, etc. He screens all this through simple half-inch screening available at any hardware store. He then spreads all this out on the tarp to dry, in shade, under a roof for several days, occasionally stirring the material to ensure it dries evenly. Once it has dried he will resift it through finer screens and winnow it with the wind to eventually have a completely clean seed that usually germinates between 90%-95%.

Brassica seed production

Only fully mature brassica seed should be harvested as it does not mature after harvesting the way that lettuce does. Seedpods should be dried down in the field and shatter fairly easily.

Note that Frank uses this same seedcleaning process for all of his brassicas that has been described for lettuce, with the exception being the method for threshing. He uses a stick or walks all over the seedpods to crush them and release the seed, or he drives over the whole lot with his pickup truck, back and forth until the seedpods are crushed. This causes no damage to dried seed. Note that the tarps and seed are laid out on grass or earth to do this, not concrete.

To clean brassica seed from chaffe Frank uses three screen sizes in the field: 3/16″, 1/8″, 1/16″. This allows him to bring home almost completely cleaned seed for further drying before his final cleaning. Once the first cleaning stage is done in the field, Frank puts the seed in paper bags or cardboard boxes, or on a tarp to dry for a further 3-5 days. This needs to be in the shade, and covered at night to keep dew off the drying seed. He puts a paper bag or envelope buried in the seed pile to monitor seed moisture levels. After a few days he checks the bag/envelope. If it feels damp, or doesn’t make a crumpling sound when he squishes it he knows the seed is still too moist and need further drying. If the bag feels dry or makes crumpling noises when squished he knows the seed is dry enough to put into airtight storage for short/long term. In storage he also keeps a paper envelope with harvest/varietal records in the seed at all times for identification purposes, as well as for use as a handy moisture indicator. Alternately one can buy a moisture meter that digitally reads moisture levels.

Diseases – identification and control

What controls the prevelance of disease? There are three major categories of control:

  1. 1. Environment – We can control disease through modifications to the environment that plants grow in, for example:

    • use drip irrigation, not overhead, to limit standing moisture on plants
    • use wider row spacing to increase air flow
    • align rows with the prevailing winds
    • remove diseased plant matter from plants or field
    • break “green bridges” that allow insects or disease to travel between different areas of field (knowing the alternate host plants for diseases can help us reduce incidence of disease, ie: over 15 common weeds are hosts to powdery or downy mildew, which can then spread to our crops)
    • soil testing to make sure soil has proper amounts of trace elements, which are critical for plants to withstand disease pressure
  2. 2. Pathogen- Some pathogens are more virulent than others, and knowing and identifying your diseases quickly can make the difference between success or failure in seedgrowing. To reduce pathogen problems:

    • check crops regularly for early signs and identify problem and take steps to control it, early control can limit pathogen population and reduce or avoid yield losses
    • create environmental conditions not conducive to disease (see above)
  3. 3. Host – The crop you grow can be more or less susceptible to disease.
    If possible, choose:

    • disease resistant cultivars
    • seed free of seed-borne diseases

Both Oregon State University and Washington State University have plant diseasediagnostic clinics. At Oregon State U., Melody Putnam will accept plant or seed samples and run pathology tests for a fee of USD$20. There is a downloadable form on the OSU website for application.

Common lettuce diseases
Tip Burn

Tip Burn on lettuces is generally a sign of calcium difficiency, and can be exacerbated by weather conditions, especially hot, dry periods. This is because as soil dries out it is harder for the lettuce plant to uptake calcium from the soil, thus resulting in tip burn. Keeping soil moist, through irrigation or mulching can reduce incidents of tip burn . Also, ensuring your soil has appropriate levels of calcium is important. Frank uses agricultural gypsum as an ammendment to increase calcium levels in his soil. Frank also noted that overhead watering of full, mature lettuce heads on a hot day seemed to result in increased tip-burn, and recommended drip irrigation to avoid this.

Lettuce Mosaic Virus

A common disease affecting lettuce is lettuce mosaic virus (LMV). It appears as yellow/green mottling (discolouring) on the leaves of plants, and as necrosis on the edges of the leaves. The disease can be spread by green aphids, which pierce the leaves and spread infection. This disease does not survive outside the living host plant or vectors like aphids. This means you cannot spread the disease yourself through handling or touching infected plants. Controlling aphids, and reducing “green bridges” in your field can stop LMV. Green bridges are other plants that can also host the LMV virus, which doesn’t only attack lettuces. This disease can be spread through lettuce seed, if you planted diseased seed you would see distorted, mis-shaped seedlings grow.


This is a fungal disease which attacks lettuce plants in their reproductive stage only, thus it is not a problem for market growers harvesting heads before they bolt. For seedgrowers, however, this disease will become a challenge to control. It appears as dried up, wilted, browned lettuce leaves that eventually become so dry they crumble from the plant. The fungus invades the plant stem, weakening it and perhaps killing or toppling the plant before seed production is completed. To control the disease strip the base leaves from the plant, for approximately the bottom twelve inches of the stalk. This increases airflow and dries the fungus out. It is permissable to leave the stripped leaves on the ground, they don’t have to be carried from the field.

Reducing weather related risk

Frank spoke briefly about reducing harvest loss due to adverse weather conditions, something he thinks will be important as climate change creates more erratic weather patterns. The Organic Seed Alliance has published a paper outlining some of the techniques Frank and others have developed to help farmers reduce weather related risk. It is available as a pdf on the seed alliance’s website at http://www.seedalliance.org/uploads/pdf/weatherrelatedriskguidelines.pdf

Recommended Online Seed Resource:
Saving our seeds, Brassica Seed Production http://www.savingourseeds.org (site also contains organic seed production guides for Bean, Cucurbit, Pepper and Tomato crops)

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