By Frank Morton
If you want to try seed growing, or if you want to specifically grow a seed that is easy, valuable, and a worthwhile contribution to your food security, Lactuca sativa (“lettuce of cultivation”) is a very good place to begin.
Most growers have seen the beginnings of lettuce coming of age. When the stem begins to elongate, we know it’s salad game over; the goodness has bolted. The stem develops a flowering head of small yellow blossoms; each blossom lasts a day and is followed in 2-3 weeks by a dandelion-like puff of fluff, each bit of pappus attached to a single seed by a fine filament. Every yellow blossom matures in this way, and after 2 months of flowering, the entire head is one sizable white aggregation of seed capsules, each blossom now represented by a small cup holding 12-20 white or black seeds, each with a would-be ticket to ride the wind. If you are lucky, you collect that seed at that moment.
For most of us, growing lettuce for seed needs to be more intentional than the above. If you live in a humid climate, summer rain will make a mess of the seed head as it matures. If your growing season is short, or if you started your lettuce later in the season, the seed may never mature. If deer bite off the bolting stems, which they relish, the regrowth will mature a month behind schedule. If stem rotting bacteria or fungi blight the maturing plant, it may die before setting or ripening seed. If a period of rain arrives just as the seed matures, the entire head may dissolve into a gray fuzzy fungus, or the seeds may sprout while sitting in little cups of water. Or, if everything else goes right, and you are just waiting for the last of the seeds to ripen, goldfinches may arrive hungry on their southerly migration and consume every seed in an afternoon. There are a lot of opportunities for failure in any seed-growing endeavor, and you only get one opportunity per year to learn all the ways. But really, except for all of this, lettuce seed is easy.
The proper planting time and growing situation are entirely dependent on your location. Most commercial lettuce is grown for seed in arid climates, like the western United States. If grown in the humid eastern US, it is advantageous if the ripening period in late summer is generally dry. The ripening heads can be rained on without damage if there are also dry periods between storms. If prolonged wet spells are expected during the ripening season, the best plan is to grow under plastic tunnels with sidewalls rolled up.
Planting time is probably earlier than you think. Because our heat units (a measure of daily temperature versus the minimum temperature required for growth) accumulate so slowly in western Oregon, and because my target dry spell is August, I plant no later than February 20th for a successful harvest. Summercrisp and crisphead varieties are the slowest to mature, and leafy types generally the fastest, with romaine and butterheads mixed up in the middle. Every variety has its individual number of heat units to maturity. I suspect seeding in April would give the same maturity date in the hot and humid East as ours.
One lettuce plant may produce 25,000 seeds, plus or minus 25,000. Seriously. But if you only grow one plant for seed, there’s a real risk you might get nothing because of the many challenges mentioned between the market-ready salad head and the mature seed head. I like to start with a minimum of 27 plants of a variety, which allows the selection of some “best performers” and some to eat. I select my favorites by putting a small stick on the north side of each plant I prefer. Strangely, it happens too often that these sticks are like curses, especially for the very favorite one. The plants really do die; of bacterial wilt, or sclerotinia, or some damned virus vectored by aphids, or a gopher, or ground squirrels. This is why you need to start with enough plants so that all the whittling down by you and nature still leaves you with a “best performer” to produce seed.
In many other crops, one or several plants are never enough to maintain an essential level of genetic diversity in the crop population. This is the case for all the normally outcrossing species (ie, those that require breeding with other members of the population, rather than themselves): corn, brassica, carrots (and all umbels), beets, onions, radish, spinach, etc. Natural inbreeders, like lettuce, beans, peas, wheat, and sweet peppers, can be selected down to a limited parentage (indeed, to a single parent) without the phenomenon of “inbreeding depression” coming into play. This “depression” of plant vigor and fecundity isn’t well understood on the genetic/physiological level, but it is well documented and has frustrated many seed savers of corn and cabbage. The natural inbreeders are “used to” this genetic bottlenecking, an evolutionary adaptation allowing individual preadapted plants to colonize large uniform areas without any associated pollinators. Dandelions have gone even further, adopting apomixis, or cloning, their windblown seeds formed in unfertilized ovules. Outcrossing crops, in contrast, require 60-300 pollinating individuals in a population to keep the population vigorous and reproductive, and they need a means to cross-pollinate. Seed savers do need to consider this as they steward their outcrossing crops.
The final plant spacing for lettuce seed plants should be at least 12” apart in rows at least 24” apart. Wider spacing allows better airflow for better plant health. Lettuce seed plants can take dramatically differing forms as they mature, varying by individual and variety. Many of the heirlooms and old commercial standards are large branching plants, nearly bushes in some cases (‘Red Sails’ red leaf and ‘Waldmann’s Green Leaf’ come to mind), while lettuces of the modern era tend to be tidy, single-stemmed, unbranched, short-statured seed plants. Those big old-style plants could produce ounces of seed each but are difficult to harvest and prone to late-stage diseases. The more compact single-head style plant produces an ounce or less seed but is efficient for harvesting and managing in the field. Some growers use stakes and string to trellis the bolting lettuce rows, especially where wind is a factor. There’s a tendency toward top-heavy floppiness as the seedhead fills, especially if rain weighs them. Once the plants begin flopping over, this invites more dampness and mold because they don’t dry out thoroughly in the sun and wind.
Selection of the best plants doesn’t happen in a single observation. I’ve counted as many as a dozen selection opportunities from seedling to seed in lettuce. If I sow three seeds per cell and germinate them in February in an unheated greenhouse, the first to germinate in each cell has something I want. If dark pigments are important, seeing those pigments in cotyledons or first leaves is also something I want. So, thinning flats that were sown 3 times too thick is a selection event if you pay attention. If mildew or aphids come to call on the greenhouse flats, that can be a selection opportunity. When the same challenges are faced in the field, that is a selection opportunity. Which plants grow fastest, which get biggest before bolting, which tastes the best, which have the thickest leaves, the glossiest coat, and the deepest color saturation? Which reds are more red? Does it head up into a blanched heart? Is the heart tip burned (a big deal)? Does summer heat cook the heart? Does the bolting stem grow straight up, or does it want to snake sideways (very bad)? Is the bolting plant a tidy single stem or a branching beast? Does it form a symmetrical productive seedhead? Does the maturing plant maintain a healthy stem and base, or are fungi feeding there? Are there virus symptoms? Are there aphids and/or caterpillars in the seedhead (usually, yes)? Did the plant bolt and make seed early (not the best)? Did it bolt very late so that the seed will scarcely mature (also a problem)? Which plants made the most and the best seed? This last item can be a good overall assessment of mature plant growth and vigor. Where most people would be most focused on the look of the salad head on harvest day, a seedkeeper will focus on overall plant health up to the drying day. The vitality of the entire lifecycle of the plant gives the best sense of adaptive fitness for the long run.
Ripening of the lettuce seed is an accumulative process. There is not one perfect time that allows the harvest of the entire yield potential at once. The seed industry has two basic approaches to lettuce seed harvest that are instructive. The “shake method” is the original, best method to get the highest yield, best quality, and cleanest seed sorted by harvest into quality grades. As the name suggests, when the ripest seed begins to fall from the earliest pollinations, seed heads are leaned over/into bins/bags/buckets and shaken vigorously to collect fully ripened seed from the head. Care must be taken not to damage the unripened portions of the seedhead or to fling seed in all directions. This labor-intensive process is repeated at intervals determined by imminent seedfall. Ninety percent of the yield potential can be harvested in three shakes of the lettuce heads. The other harvest approach is the “one cut method,” when you wait a bit after the first seedfall, then cut whole plants onto fabric in the middle of the yield curve. Plants are threshed 7-10 days after ripening, preferably in shade. This is less work for less yield of a lower quality. My alternative to the one-cut method is the “one pull method,” where the plants are pulled with the roots (rather than cut), so they remain alive for nearly a week, maturing longer than severed plants. This improves both yield and germination over the cutting method. Another alternative (especially useful for trellised plants) is the “head-cut method,” where seedheads are snipped from the stems at optimal maturity and threshed at once.
After seed harvest, the seed is moist, metabolizing, and full of insects. It is important to spread the fresh harvest out to dry in a shaded, breezy location so that aphids, spiders, lady beetles, lygus and minute pirate bugs, micro wasps, and syrphid larvae can crawl out, which they will. After drying several days or a week, when all the creatures have evacuated and the leafy chaff is drying out, you may begin the cleaning process by rough winnowing in a soft breeze outdoors. Start this by rubbing handfuls of seed/fluff over a bin in a gentle breeze. The seed should fall into the bin; much of the fluff will drift away. Repeat this. Put the seed/leaf/stem mixture onto a 1/8” hardware cloth screen. The seeds and fine chaff will pass through. Winnow the seed and fine chaff in a breeze again, but this time with two bins side-by-side, so the seed falls into the upwind bin, and light chaff, dust, or any mistakes fall into the downwind bin. (Winnowing is an entire subject unto itself.)
Screening and winnowing are used in alternating cycles to clean the seed. After winnowing away fines and dust that clog up screens and are harmful to breathe, lettuce seed can be passed through a window screen (1/16th inch, square) with some determined, careful shaking and maybe “bouncing.” Sticks and flower parts will stay on top as the lettuce passes through. If you then pass the seed quickly back over the same screen without much shaking, fine seed, heavy dirt, and “crippy crap” will bottom out, leaving the bulk of the crop atop the screen fairly pristine. This is your prize.
This is the basic lettuce seed-to-seed process. There are variations and options, many more ways to complicate matters by collecting packets of single mothers for future comparison, selections of unique traits, or “off-types” that may be cool crosses. Lettuce was, for me, an inviting gateway to the world of seedkeeping.
Frank owns and operates the Wild Garden Seed company with Karen,
based in Philomath, Oregon. They are known for farm-original varieties of
salad greens, vegetables, herbs, and flowers.
This full article can be found and was originally published on the Wild Garden Seed Company’s website, wildgardenseed.com/articles/how-to-grow-yourself-some-lettuce-seed.
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