Every gardener who’s tried to collect seeds and keep them for the next year can tell you that seed saving is quite tricky. If you harvest the seeds before they’re fully mature, they will not germinate.
But more importantly, how you process the seeds after harvesting will determine their health, vigor, and longevity. There are two ways to process mature seeds, wet and dry processing.
What’s the difference between wet seeds and dry seeds?
Wet seeds are those seeds that mature inside of a moist fruit such as the seeds of tomatoes, watermelons, squash, and pepper. The fruit has to be fully ripe or even overripe before you can collect the seeds. Dry seeds are those seeds that mature in a dry and brittle seed head. Most seeds are dry seeds and you can harvest them when the seed head crumbles or snaps open with little pressure.
How you harvest each type of seed depends on its species. Read on to find out how best to harvest, process, and store both wet and dry seeds.
Harvesting, Drying & Storing Dry Seeds
The majority of the seeds you grow in your garden or greenhouse fall under the dry seed category. These are seeds that develop inside of a pod, tract, capsule, or any other seed head.
It’s easy to monitor their development and tell when they’re ready to harvest. Changes in the color and texture of the seed head from green and moist to yellow, brown, black, and dry are dead giveaways.
Dry Seed Examples
Examples of dry seed crops that grow in the garden include onions, beans, peas, corn, nuts, and lentils to name but a few.
Harvesting Dry Seeds
Dry seeds are arguably easier to harvest. The tricky part is often deciding when the seeds are ripe. As the seed head ripens, its color changes from green to yellow and brown or black. The seed head then loses its moisture and dries up.
Hold the pod or capsule in your hand and press it gently. If it cracks or crumbles, you should start harvesting the seeds. If the seed head bends under pressure, it’s still moist and the seeds are not ripe yet.
Always harvest dry seeds on a sunny and dry day. If it has rained recently, allow the seeds more time to dry on the plant before you collect them. Sometimes weather conditions such as frost would force you to harvest your seeds even when the pods are still leathery.
In that case, pull out the plants by the roots and keep them in a dry place. The seeds would absorb more nutrients from the plants and continue to ripen.
Completing the Drying Process
Even if the seed pods are cracked open and spraying the seeds everywhere, that doesn’t mean that all the seeds or all the pods are fully dry. Before you can start processing the seed heads, you need to let them dry out.
Spread the harvested pods on a bench in a greenhouse or an airing cupboard. Leave them for a few days until all the moisture is gone.
If you’re in a hurry and want to dry the seeds fast, you can put them in the oven. Spread the seed heads thinly on a tray and place it on the bottom rack.
Cover the tray with a cooking sheet and set the oven to the lowest temperature around 200 degrees Fahrenheit. Stir the seed heads with a spoon every half an hour.
They should be dry within 3 to 4 hours.
Some seed heads need to be trampled or beaten while others can be shaken to loosen and extract the seeds. This process is called threshing and it varies depending on the type of seed heads you’re dealing with.
As long as the seed heads are fully dry, then threshing is a straightforward task. Your goal is to crush the pods or capsules surrounding the seeds to free them up.
In the case of grain crops such as rice and wheat, you’ll need a machine to process the crop. But if you’re just growing a small patch in the garden, then you can thresh the pods by trampling them with your feed in a bucket or on a clean sheet.
You can also crush them with your hands. Always wear gloves to protect your hands against splinters.
Threshing often leaves you with a pile of seeds mixed with a lot of chaff and plant debris. Winnowing allows you to separate the seeds from the chaff. You can do this by dropping the mixture from an edge and letting the wind blow away the chaff while the heavy seeds fall to a sheet on the ground.
You can also use large sieves to winnow the seed-chaff mixture. Just make sure to use the right mesh size so as not to lose seeds in the process. For some tiny and light seeds such as artillery plant seeds and torenia seeds, you can use static electricity to pick the debris.
Swirl the mixture in a ceramic bowl then empty it in another ceramic bowl. Repeat. The debris will cling to the sides of the bowel while the seeds drop to the bottom.
Once you have your dry seeds winnowed, you can store them. Ideally, you should store them in airtight containers such as glass jars with gasketed lids. Before you close the lid, drop a silica sachet, like the one that comes with packaged dry foods, in the container with the seeds.
Label each container with the name of the seeds and the date of storage. Keep the seeds in a cool, dry, and well-ventilated place.
Harvesting, Drying & Storing Wet Seeds
Wet seeds are those seeds that develop and mature inside flesh and succulent fruit. The only indication that the seeds are ripe and ready for harvesting is when the fruit itself ripens or becomes overripe. Only then can you split the fruit open and extract the ripe, albeit, moist seeds.
Wet Seed Examples
Whenever you have a fruit that contains a seed inside of fleshy and moist pulp, then you have wet seeds. Examples include watermelons, peppers, squash, guavas, cucumbers, pumpkins, tomatoes, courgettes, egg plants, and papayas among others.
Harvesting Wet Seeds
Since you have no access to the wet seeds on the plant, you’ll have to monitor the fruits for signs of maturity. In the case of cucumbers and squashes, you should allow the fruits to become overripe to ensure that the seeds are fully developed. Once the fruits are ripe, collect them, open the fruit and extract the seeds inside.
Wet seeds often have pieces of pulp or other goo clinging to them when you take them out of the fleshy fruit. Depending on the type of wet seed and the type of goo, you might have to ferment the seeds to extract them cleanly from the goo.
How To Ferment Seeds
Tomato, watermelon, and cucumber seeds often have sacs of goo surrounding the seeds. The goo preserves moisture for the seed to germinate as soon as the fruit breaks open. But you want to store the seeds for a long period of time, so the goo has to go.
You can get rid of the gelly by fermenting the seeds slightly. Here’s how to do it.
- Fill a bucket with the gooey stuff and keep it in a dark, warm, and damp corner away from the sun.
- After a few days, you’ll notice mold on the surface. That’s a good sign that the material is getting fermented.
- Fill a cup with the goo and pour it into a glass bowl. Add 5 cups of water to the fermented goo.
- Put on gloves and break any lumps with your fingers to release any trapped seeds.
- Use a ladle with a long handle to stir the liquid thoroughly. This will separate the fermented goo that floats from the heavy seeds and crud that drop to the bottom.
- Discard the floating goo and dead seeds and keep the heavy stuff at the bottom of the bowl.
- Repeat with stirring, breaking lumps, and rinsing until you have only healthy seeds in the bowl.
- Do the same for the rest of the fermented goo in the bucket.
- Rinse the seeds in cold water and put them in a strainer.
Once you have the seeds cleaned up and goo-free, you’ll need to spread them out to dry. This time, lay the seeds on a sheet in a thin layer and keep them in a dry place. It might take them a few days to dry out completely.
Some seeds like tomatoes would make a clump. Break the clump gently between your fingers to separate them.
When the seeds are completely dry, store them in air-tight containers and label them. Keep the seeds in a dry and well-ventilated place for when you need to use them.
Wet seeds develop and mature inside of fleshy and succulent fruits. When the fruits are ripe, you can extract the seeds, clean them up, and when they’re dry, store them in air-tight containers.
Dry seeds mature inside of seed heads that need to be crushed or shaken to extract the dry seeds. After threshing and winnowing, the dry seeds are ready to store in labeled containers.