Saving Seed in Hawai’i: Processing, Drying, and Storing Seed in the Subtropics
Keeping seeds dry and able to reproduce into the future in our subtropical climate is quite challenging. Seeds grown and saved in Hawai’i have different needs than seed you might have grown in your gardens on the continent. Leaving seeds out to dry and admire on your kitchen table will sometimes work, but only if you will be replanting them very soon. Otherwise, they need to be dried down correctly and stored in a safe space. Dried correctly and kept well, many garden seeds can be kept for up to 10 years. The guide words here are cool, dark and dry, which will keep them stable until it is time for replanting. Fall is an excellent time to collect seed, and many of you may be thinking about saving some seed from the plants that you are growing in your home garden. This Blog will focus on the most important aspects of keeping your garden seed viable into the future. For a deeper dive into why save seed, See the Resources Section at the end of this Blog.
Collecting Seed From Your Garden Plants:
The first consideration is that plants finishing their lifecycle and seeding will be in your garden beds a lot longer and hopefully finishing their cycle in the drier times of the year. Some plant varieties can be rained on and still produce healthy seed, like peppers, tomatoes, eggplant, beans, etc. - varieties where the seed is inside either the fruit, vegetable or pod. Other varieties like lettuce, broccoli, or any of the leafy greens (and most flowers and herbs) cannot withstand constant moisture when seed is maturing.
Check your maturing plants often, observe the seed forming process, and when you think the seed is fully ripe, carefully remove for processing. There is a lot of information needed here, so I suggest that you have at least one good book to guide you, such as Suzanne Ashworth’s Seed To Seed. There are used copies for about $7, and there is an online PDF you can download! The Organic Seed Alliance also has a great downloadable seed saving guide here: https://seedalliance.org/publications/seed-saving-guide-gardeners-farmers/ There are also more references at the end of this Blog.
There is a science and art to seed saving and you can begin to learn by saving seeds from one of your favorite crops. Once your desired seed crop has fully matured, flowered and has produced seed pods or stalks (or very ripe fruit) the next step is processing. Each crop variety is processed in different ways. The most important aspect is to make sure that the seed stays dry. If it is a very dry time of year, you can leave seed on the plant to dry, but in many places in Hawai’i that isn’t possible because of frequent rainfall. If you are collecting seed from varieties like tomato, cucumber, pepper, squash, eggplant, okra, any crop where the seed is inside, make sure that the fruit or vegetable is fully ripe before you open and scoop out the seeds. Use the “wet processing” techniques found in the guides I mentioned above. With many vegetables you can both save the seed and eat most of the vegetable.
If you are growing beans to seed, leave the pods on the plant to dry during times of dry weather, and if that's not possible, then wait until the pod turns yellow or changes color before harvesting individual pods. I usually bring them up to the house, open the pods and begin drying the seed down on a plate in my kitchen.
If you are saving seed from a plant that makes a stalk, like lettuce, arugula, mustards, tatsoi, broccoli, radish, etc. cut the entire stalk when mature. Before you harvest the stalk, be sure to open a pod and check the seeds inside, making sure the seeds inside are not still young and green. Generally, you should see mature seeds at the top of the stalk, which will be full and plump and will have changed color from green to light grey, brown or black. Seeds at the bottom of the stalk may still be less mature, with slimmer seeds that may still be green or just starting to change color. Once you are certain your seeds are mature, cut the stalk and dry down for a week or so (before processing!) by hanging stalks to dry on a breezy lanai. With lettuce, cut the stalk when most of the flowers have opened and have formed a white fluffy puff. You should be able to pull off individual seeds easily at this point. If not, give them a bit more time and try again. When lettuce seeds are ready, the seed pod with the white puff will be starting to turn brown where the stem is attached to the stalk. The entire stalk can be put into a brown paper bag or bucket and dried, or laid out on a sheet to dry on your lanai. Lettuce sometimes shatters, so you want to make sure you are catching all the seed.
Drying Your Seed Before Storing:
One common mistake in the subtropics is to store your seed in a jar, packet, or other container before it is fully dried down. Seeds that are stored before being fully dried down will rapidly lose their ability to germinate. Seed can only be dried down in the open environment when the temperature plus the humidity equals 100 or less!
percent relative humidity + air temperature in degrees Fahrenheit = 100 or less
The temperature in my house is usually in the 70s and relative humidity is 80% or higher! In many areas of Hawai'i the humidity will go up into the 90% range each evening. That means it will be impossible to dry seeds down in the house or lanai without some extra help. Sometimes I use a fan on the seed for a few days and up to a week to dry up any leaf material still on a stalk and to begin to dry the seed down, before putting it in one of my dry buckets.
Here is my list of materials needed to create a dry bucket.
· A 5-gallon bucket with a tight fitting lid.
· Silica beads, or my favorite, the Eva Dry Unit (about $23 available on the internet). Silica helps to absorb moisture in the air slowly. Plug it in to re-dry the silica beads.
· A small hygrometer. You can usually buy a small pack of them very inexpensively. They are about $4 each. Usually they show both temperature and humidity which is very handy.
· I use paper plates to create a few levels inside my bucket so that I can dry a few different seeds at once. Tip: small seeds dry quickly and large seeds slowly. They should be in different buckets.
· UC Davis has made a nifty Dry Card: https://horticulture.ucdavis.edu/drycard
Once your hygrometer says the air in the bucket is 30% or lower humidity it is safe to remove your seed and store safely away for the next planting. At the end of this Blog you can find additional resource ideas for drying seed in the subtropics.
Storing Seeds for the Future
Seeds want to be cool, dark, and dry for long term storage. I store my dry seeds in small ziplocks and then put them in a tight Tupperware container in my small seed refrigerator. Refrigerators run at about 49 degrees which is a good temperature for preserving seed as long as the container is tight and free from moisture. Again, if you decide to store your seeds in the fridge, make sure the seed is in a tight container as some refrigerators can be humid.
Most modern refrigerators are humidity controlled and you can actually dry your seed on an open plate as the humid air is drawn out of the seeds. You can always check the humidity levels of your refrigerator with your hygrometer or dry card to be sure before you try that technique. These simple tools will support you to enjoy great success and longevity for your precious seed. Learning to save seed is both a science and an art. The knowledge and skill of seed saving will develop over time through the practice of doing and will reconnect you to the cycles of life that surrounds you.
For a deeper dive into the story of why save seed and seed sovereignty, as well as the historical perspective about how we got here, please enjoy our previous discussions on the topic.
1) A Civil Beat IDEAS Essay: Seed Diversity is Vital to the Future of Food