By Brett Grohsgal
The number of mother plants you use to keep your seed stocks healthy and vigorous is a key issue but one that is readily resolved by using rules of thumb for each crop. On farms with more than a 1/4 acre per cultivar, you should have plenty of mother plants available to select enough superior individuals to avoid inbreeding depression. Don’t limit yourself by collecting from too few superior mother plants. The following is a list of some crops followed by each one’s recommended bare minimum of mother plants for seed collection, plus the rough number, in parentheses, that our own farm harvests annually for seed:
arugula: 50 (1200)
other Brassicaceae: 30 (1200 per genetic line)
chili: 10 (20)
cucumbers: 20 (30)
cutting flowers: highly variable, but minima of 10- 50 (10-200)
lettuces: 20 (200 per line)
musk melon: 20 (30)
squashes: 10 (50 per line)
sweet peppers: 20 (30)
tomatoes: 30 (75 per line)
watermelon: 30 (100 per line).
Choosing the best mother plants from which to collect seed is only slightly harder than normal harvesting. There is a great overlap in this area and in the selection step in more rigorous genetic management. We select mother plants based on their size, their vigor or amount of fruit set, their fruit quality, and/or their tolerance of problem diseases. Leafy greens are easy: I decide how many pounds of seed I need from each line, and from that what percentage of the beds need be seed-harvested. I then walk through, assess flower-stalk thicknesses as my primary measure of vigor, and estimate what thickness will delineate the best 10%, 30%, or 50% of mother plants. At this point the farmer could delegate by telling a worker, for example, “Please cut and gather all the collard stems at ground level that are thicker than a pencil at 2” above the soil surface. And only harvest stems that have ceased flowering and have seed bulges in most of the pods.” So in leafy greens vigor is approximated by survival of the prior winter and then by stem thickness. The harvesting itself is done with machete or sturdy flower snips; bundles of stalks are placed in the traffic row to be picked up later with a vehicle.
Tomatoes and other fruit-bearing summer crops should not be delegated and are more difficult. One of our goals is incremental improvement in tolerance to microbial pests such as the wilts in tomatoes and mildews in squashes and cukes. All tomato or pepper plants with any TMV (endemic in our area) or with zero tolerance of the wilt fungi are destroyed early, as are more mildew-prone squash or cuke plants. Later, fruits are harvested only from those mother plants showing the least, if any, infection, and with excellent fruit quality, and with superior fruit production or size, and with excellent general vigor. Harvesting of fruit for seed only occurs twice or so per line per summer, but remember on those days to get your seed fruit ahead of market fruit. Regardless of the crop, you, the farmer, know what you want to see in vigorous survivors, in superior mother plants, and can adapt your criteria accordingly.
Types of seed
For the purposes of farm-level seed processing, vegetables can be roughly grouped into 3 categories:
•The first group, the lettuces, the cole crops, and okra, are all taken from the field in the long flower-stalk form, spread out on plastic with good labels for days to air- and wind-dry, turned periodically to even out this drying, and then threshed manually by crushing bundles of the dry stalks (pod end only) on some surface or a thigh. The seed and chaff drop onto a collecting sheet of plastic. Lettuces can also be simply rubbed; their seed heads aren’t usually as resistant to crushing as are the brassica’s or okra. We then use sieves of screening or hardware cloth to get rid of stems and bigger chaff. Finally we pour the seed/fine chaff mix from one large wash tub into another about 4’ in front of a big industrial fan. The lighter chaff blows away and leaves you the heavier seed. Be aware that the difference in densities between seed and chaff is what drives this step; the closer the densities of seed versus waste (e.g., in lettuces), the easier it is to blow away the seed. I strongly recommend laying down a white sheet downwind of the big wash buckets. This lets you easily inspect what’s being blown away and adjust your fan speed, tub height, or distance from fan accordingly. You can also use prevailing winds in lieu of a fan, but changes in wind speed and direction can become both annoying and costly. Beans and peas could be handled in this way or can be directly gathered in the dry pod form. Incidentally, what I’ve described here is only how we do these vegetables now, for seed lots per line of 5 pounds or smaller. I long for the day that we have a mechanized, affordable, small-scale thresher.
•The second vegetable category includes most of the summer fruits: peppers, melons, cukes, and squashes. After harvesting full-ripe or over-ripe fruits, we store these in the shade in single layers for further curing. This period can last only a few days (e.g., in peppers) or as long as five weeks (e.g., in winter squashes). During this time those fruits are in emergency mode: they have been removed from their mother plant and are feverishly trying to further ripen, and devote resources to, their seed. A small amount of rot is usually acceptable, but proceed quickly to the next step once this is noticed. Cut the fruits in half to expose the seed cavity and strip the seeds from the fruit into large buckets. At the stripping stage two genera merit special care. Hot peppers require tight-fitting latex or nitrile gloves. Watermelons do not ripen a lot off the vine and you may want to let trusted friends or workers take home fully ripe, premium fruits from your best mother plants on the proviso that they save, wash and label those seed for you. This can save you a lot of work. Regardless, with this category try to leave as much pulp as possible behind, and wash the seed a lot to further remove pulp or sugary films. Then spread the seed out on screening, in shallow boxes, and fully labeled in a well ventilated barn or porch to air-dry for a minimum of 2 days. It is imperative that you dry these out of reach of rodents or birds: over the years we have lost at least 6 extremely valuable lots of melon or heirloom squash seed to mice or to songbirds.
•The last processing category includes the tomatoes. Use only fully ripe or slightly overripe fruits. First cut the fruits in half to cross-section the seed cavity. Do this with plum and beefsteak types; skip any cutting with cherry or teardrop tomatoes. Then squeeze out the seeds into a large clean bucket. With certain low-seed lines, especially plums and some heirloom tomatoes, you may choose to scrape out the seed cavities with your finger to maximize seed yield. After you’ve gotten all the seed from a given cultivar, pour the seeds with their juice into previously labeled tall jars (e.g., quart canning jars). Maximum depth of the juicy suspension can be 4 or 5 inches; use a bigger jar, or more jars, if needed to avoid greater depths. The tomato seeds plus their juice are then fermented for 3-6 days. This entails swirling the jars individually 1 or 2 times daily, waiting for settling, pouring off the scum, mold, and/or pulp carefully, and then adding any water needed to keep at least an inch of fluid above the seeds. This fermentation step is vital because it removes the sugar coat around each seed that would cause clumping were you to dry the seeds right after harvest. Too brief a fermentation leads to clumps of seeds next spring that aren’t easily separated for good sowing. Too lengthy a fermentation, or one with too little stirring or removal of mold, leads to anaerobic death of large percentages of the seed. To avoid forgetting about these fermenting jars during our busy summer season, we place them in an open box right in the main work area of the barn, fully dated and with a projected end date for the fermentation. If you leave them in the house the inevitable fruit flies may haunt you. After the fermentation stage is done, carefully decant off the upper layers of mold, pulp, and other trash, leaving the seeds in their now rather watery juice in the bottom. Now comes the stage that kills any Fusarium or Verticillium spores that might re-infect you seedlings next year. Disinfect the seeds using a 10% bleach solution (1 cup regular bleach in 9 cups clean water treats the seed left in about 5 quart jars). Time this stage well: the dilute bleach is added to each jar, swirled generously, and 90 seconds after the seed first saw the bleach, pour off the bleach and immediately add fresh water. Let the seeds settle by waiting 15 seconds after swirling ; decanting off your bleach water or rinse waters then doesn’t waste much seed. We rinse at least 4 times, and timing here isn’t important. The seeds are then drained onto pieces of nylon window screening that has been stapled into fully labeled wooden boxes or cheap quart berry baskets. Let air-dry for about three days. Every day break up any clumps with your fingers and stir the seed around to attain even drying, and as usual do this in a mouse- and bird-free space. The seed will feel dry and light when they are done.
Supplies and storage
The supplies that you will need for this beginning level of on-farm seed processing are simple and inexpensive: snips or a machete, plastic sheeting, a marking pen, a fan, 2 large basins, hardware cloth, nylon window screening, harvesting crates, 5-gallon buckets, wooden crates or berry baskets, bleach, canning jars, and a clock. On our farm these supplies plus our labor process the seed for many acres of production
There is no point in saving seed only to then reduce its vigor by storing it the wrong way. All vegetable and flower seed on our farm is wrapped in ziploc bags (gallon or pint) that are fully labeled with the line’s name and year of harvest. Groups of seed lots (e.g., all heirloom tomato cultivars from a given year) are then put into a larger bag and sealed. Cucurbit and flower seeds are not frozen, only refrigerated, but all other vegetable seed are put into a deep freeze (if you have to use an above-the-‘fridge freezer, triple-wrap your seed lots). No seed is stored at room temperatures except purchased cover-crop seed, sown only weeks after purchase. We wrap so well because refrigeration slowly dries out seed and food. And we refrigerate or (better) freeze seed because seeds are alive and we need to slow down their metabolism now for better vigor when we plant them. Done this way, pepper seed lasts 7+ years, tomato seed at least 4 years, cole crop seed between 3 and 5 years, and cucurbit seed stays vigorous 2-3 years. The fact that well-stored seeds stay vigorous means that every year I only have to process seed from a subset of our crops; the rest is valuable inventory.