SEED COLLECTION 2: Proper Cleaning and Storage

A “Hindsight is 2020” Series

By Justin Daniel, CNPS-San Diego President & Field Trips Chair and Grower & Collector

There’s a very detailed process to saving seeds for a seed bank such as the Svalbard Seed Vault. Glimpse this world by browsing some excellent articles at: https://academy.saveplants.org/best-practices/cleaning-processing-drying-and-storing-orthodox-seeds

Collect the seed bearing parts of the plant

This series of articles on seed collecting is for those of us who are saving the diversity of San Diego County at generally less than a dozen plant species at a time. To accomplish this admirable feat, it still takes time, practice, and trial and error. Rookie mistakes are great learning experiences, especiallywhen it’s someone else that makesthe mistake first. Opening up a bag of recently collected fruit to find a moldy mess is easily avoidable by prioritizing cleaning and sterilization of fruits immediately following collection, or by allowing the decay process but with occasional actions to stymie fungal growth. Quick freezing and near freezing stratification helps preserve those species that are tolerant of the low temperatures. Opening up a packet of seeds only to find empty husks and some very fat and happy larvae in the place of the endosperm is avoided with a thorough cleaning and screening (described below) followed by quick drying using desiccation (i.e., dehydrator; silica gel/bead packets) or a drying rack .Also, as an aside, it’s best not to let those larvae escape, only to be found by a startled family member who is now on the warpath in the living room, swatting at curtains and light fixtures and vacuuming every surface at 2 am. (That’s a purely hypothetical scenario, I assure you!)

So, picture yourself sitting down at a desk or table, dusty and weary from a few hours in the hot sun collecting fleshy fruit, dry pods, fluff covered achenes, and stony nutlets, and with a bag or two of an always miserable spiky/hairy/sticky/stinking/stinging/spider-infested mess with seeds presumably hiding inside. (If you’ve ever collected a variety of Phacelia species, you know what I’m referring to). First things first, grab your drink of choice and put on some music because the next steps are going to take a little while. If you have more important distractions at this point, at least open the bags to circulate air and loosely place the moister plant material into a paper bag or spread out it out on trays or racks (with a label) to dry until you can get to them. Keep wet berries in a sealed bag and place them into the sun to decay a little in the UV.

An excellent 2008 article by Matt Teel on seed collection is at: https://www.cnps.org/gardening/california-native-plant-propagation-4014

Use a tray to contain the plant material

When ready to process the seeds, provide at least two large, lightweight hard trays per species. Have a bin ready for the chaff. Wear shoes, eye protection, and a dust mask (at least) while doing this. Have gloves or an old pair of rubber soled sandals at the ready, too.

FLESHY FRUIT: Soak the fruit in warm water using a screen or colander and large bowl. When properly mushy, most seeds break away from the fruit with a gentle massage. Allowing the fruit to decay for a few days does wonders for separating fruit pulp from seeds, too. Adding vinegar (acetic acid) can help dissolve stubborn tissue, and with increasing concentrations, the acid removes layers of thick seed coats. Seeds ought to fall to the bottom of the sieve or float to the top, depending on the species and maturity of the seed. Drying the seed and the pulp together is fine, and then it can be manipulated to separate the seed and dried pulp for easy screening. Screening and ‘blowing’ (described below) the dry seed later will separate the seed from the pulp well enough.

DRY PODS: If you’re lucky, the seeds will fall out if you tip the open pods over, or keep the pods in a dry place until they pop and release the seeds. If you’ve decided to go forthose tougher ones, the processing is best done with tools. Harder to crack pods, like Keckiella or Penstemon, need to be rolled with a rolling pin against a hard surface, crushed lightly in a mortar and pestle. Crushing them between sandal soles works pretty well, too. Don’t let anyone see you do this, but that is up to you and whomever is now watching you gyrate with sandals on your hands as seeds fall out between them, loudly hitting a tray below. Screening and blowing comes next.

FLUFF COVERED SEEDS: Chances are a slight breeze is going to blow some of the fluff into your face - fair warning. Grab some fluff and use the stereotypical villain’s hand wringing technique to make the seeds drop out. For asters with long, easily bent and breakable seed, and for most grasses, gentle pulling will separate the pappus or lemma & palea away from the seed. Then, screen and blow.

STONY NUTLETS: Manzanita fruit and others with dry, tough fruit with a stone inside can be crushed wet or dry. Dry stones can be split with pliers, or treated for germination without this process. Occasionally, tough fruits are sold and planted intact.

THE MISERABLE REST: For those seeds that present a challenge, the processing is as novel as the problem. Protective gear and basic tools found in the shed or kitchen are chief among the solutions. Sticky seeds can be neutralized a bit with an agitated wash with water and a few drops of liquid detergent, then rinsed in hot water. Have a vacuum, lint roller, and paper towels handy for cleaning up. Experimentation with fire (done safely, please!) can help burn away parts of the fruit while treating the seed for germination, which I usually reserve for fire followers.

Screening and blowing can be done independently of each other or in turn, but the idea is to get the seeds mostly or fully free of any chaff, sticks, leaves, dust, etc. Stacked screens of different mesh size really help to quickly separate a loose mix of materials based on size. Blowing can be done mechanically with an adjustable blower machine, or be done manually using a wide plastic tray. By placing all of the seeds and material at the top of an inclinedtray, you can “tap” the tray with anold credit card or similar device to cause the dry mixture to separate. Round seeds fall away quickly, and with a little effort, the results are 95%+ seeds. Try rubbing the seeds and chaff at different heights in a calm breeze, or simply lightly crushing the mixture together to further differentiate seeds from the rest. Your results should be similar to the seed photos of Southern California native plants by John MacDonald at: http://www.hazmac.biz/seedphotoslistgenus.html

Disinfect the seeds with a quick wash of diluted peroxide if the seeds have a hard coat. A light spray of 1 part bleach to 10 parts clear water; OR light spray of white vinegar protects seeds from fungus. Allow every type of seed to dry completely. Silica gel packets do this well by adding one or more packets to the seeds in an air tight container. There are different methods for doing this, but ensuring the moisture content is very, very low is important for stable seed storage and for preventing insects and pathogens from destroying your seeds (and the time / money you spent collecting). For species that grow in areas with a freezing cycle, place the seeds into a freezer for about forty minutes to an hour to be sure any insect eggs or larvae have been neutralized.

More info for treating seed is available at: https://www.roguenativeplants.org/wp-content/uploads/2018/12/Processing_Seed_California_Native_Plants_Rancho_Santa_Ana_BC_2009.pdf

Seeds should always be stored in a cool to cold, dry environment in packets labeled with times and location(s) of collection, species, and collector. Additional information can be a reference number for filed pictures of the mother plant or GPS data, etc. Review the provided links and when/if seed sorting parties are possible again, come out and meet people who have their own techniques. The accomplishment of making a clean, dry packet of seeds ready for growing or further treatment or sharing with friends is something that’s really grown on me and I hope you as well.