How to Harvest Your Own Seeds

Susan Patterson
various seeds

After enjoying the flowers, fruits, and vegetables you grew in your garden, there's one activity that's just as rewarding: harvesting seeds. While it's hard to ignore the bigger and brighter hybrids flaunted by their catalogs, you'll enjoy substantial savings by growing plants from your own seeds and gain satisfaction in the process, too. Naysayers will say the plants grown from seeds don't come true, but anticipation is half the fun.

When to Harvest Seeds

Summer and fall are the main seed-harvesting times because by then spring and summer flowers would have set seed. Harvesting can happen in spring for early-flowering and short-lived plants. It may extend to winter for fruits that mature in late fall. Keep a watch on the plants you want to grow from seeds, and you'll see the seed heads and fruits maturing and becoming ready for picking.

How to Harvest Dry Seeds

Plants make flowers for the very purpose of making seeds from which their next generation can grow. It is the flower heads that eventually become seed heads in many plants.

When flowers wither in your garden, you may be diligently removing them to encourage more flowering. This is called deadheading. If you want to harvest seeds, you should allow the withered flower heads to remain on the plant until the seeds inside them mature. Even the stalks of flowers that grew from bulbs can be left on the plant to make seeds. The green portion left behind when the petals die off continues to grow and support the seeds inside. When these seed heads start changing color or start to open up, you should be ready with your seed collecting paraphernalia.

Step 1: Gathering the Seed Heads

The way you gather the seeds depends on the plant's structure.

Compact Flower Heads

For compact seed heads that do not burst open (indehiscent), you can snip them off with a sharp scissors when they are nearly dry. Marigolds, zinnias, dahlias, coneflowers, globe amaranth, and pinks can be collected this way.

Legume and Flower Pods

Poppy head pod
Poppy head pod

Some seeds, like those of runner beans and peas, come packed in pods that grow in the place of flowers when the petals are gone. Don't allow them to dry on the plants, or they may burst open (dry dehiscent), spreading the seeds around. You can harvest the pods of poppy, sweet pea, morning glory, beans and okra, when they are nearly dry.

Large Seed Heads From Various Plants

Plants with large flower bunches have large seed heads too. The bunch of amaranths, celosia, cleome, cilantro, Queen Anne's lace and ornamental grasses should be first placed in a large brown paper bag and tipped down before cutting them off the plant.

Leafy Vegetables and Herbs

Green Thai basil in flower
Green Thai basil in flower

If you're growing green leafy vegetables such as spinach or collard greens, or some herbs like mint, cilantro, or basil, you may not see any flower heads on them. That's because you're harvesting them regularly. But if you let one or two plants to grow without snipping their leaves and stem tips, they will eventually go into flower. These flower bunches will set seed after the flowers die. You can harvest the whole bunches when they start to yellow or dry up.

Gardeners should know that spinach has male and female plants, and you get seeds only from the female ones. Collect the very tiny seeds in plastic bags by keeping the nearly dry flower heads inside and crushing them with a rolling pin.

Conifers

Collect mature cones that are slightly open and dry them in a warm but shady place until they open up releasing the scaly seeds. Fresh seeds of some conifers sprout if they are planted immediately.

Note that once they are dried and stored, they will have to undergo a long stratification process before germinating.

Step 2: Drying

Place the collected seed heads of each type separately between sheets of newspaper. Keep them in a shady place for a few days to dry further.

Step 3: Separating the Seeds

Separating the seeds is called threshing. Some seeds may come out of their pods on their own or when you shake them inside a paper bag. Examples of separation methods include the following:

Marigold seeds
Marigold seeds
  • Grains are threshed by beating or stamping.
  • For marigolds and zinnias, you should open up the seed head manually to get the seeds. You can find the seeds among the other flimsy material called chaff as the seeds will be mostly darker in color or plumper than rest.
  • For small seeds of amaranth and celosia, rubbing between the hands or crushing with a rolling pin may be necessary to separate the seeds.

Step 4: Cleaning

There will be lots of stuff in the seed heads other than seeds. If you're directly sowing the seeds after harvesting them, cleaning is not necessary, but seeds that are not cleaned may spoil faster on storage. Some seeds are big enough to be hand-picked, but for others you may need to winnow them or use a strainer with holes just the right size for the seeds.

How to Winnow

Winnowing seeds using a fan
Winnowing seeds using a fan

You can use a hand fan for winnowing small seeds and a hair dryer at 'cool' setting for heavier ones.

  1. Put the seeds in a bowl and pour them on to a newspaper in a continuous stream as you fan the stream gently.
  2. The chaff will fall farther away from the seeds as they are lighter.

For small quantities, you can just blow into the seeds as you pour them out. Larger quantities might require the use of fans.

Step 5: Storing

When the seeds are completely dry and free of debris, you can store them in labeled glass bottles with tight caps. The label should contain the plant's name and date of collection. Seeds have a limited period of viability as their chances of sprouting reduce with age. You can add details such as color, size, and other characteristics, too.

How to Harvest Wet Seeds

Some seeds are wet because they are inside fleshy fruits. Cherries, plums, avocado, mango and almond have a single seed inside, while others like apples, pears and oranges have a few more. Some like pomegranates, kiwifruit, passion fruit and tomatoes are so full of seeds, they get eaten. Even though tomatoes are often considered vegetables, they are actually fruits, as are peppers, eggplants, bitter melons, and cucumbers.

If you have any fruits or vegetables containing seeds inside that you want to harvest, you should let them stay on the plant/tree until they are ripe.

Step 1: Gathering the Fruits

Seeds for the purpose of planting should be harvested from fruits/vegetables ripened on the plant. The seeds inside fruits that are not fully ripe may be immature. Fallen fruit, even slightly rotting ones, are the best. Collect the different types separately.

Step 2: Separating the Seeds

Remove melon seeds
Remove melon seeds
  • It's relatively easy to separate the seeds from an apple or a ripening pepper. Just cut them open carefully and tip the seeds in to a bowl.
  • For fleshy tomatoes, tomatillos, kiwi, and passion fruit, you'll have to scrape out the seed-containing pulp into a bowl of water, using a grapefruit spoon.
  • Cucumbers, melons, squash, and papaya have a central area where the seeds are concentrated. Remove that into a bowl.
  • Peaches, plums and cherries may give you fruits true to their parent plants. Allow the fleshy fruit to rot a bit further before you dig out the pits. You have to break them with a hammer to get the almond-like seed inside and store in the refrigerator.
  • Juniper seeds should be stripped off all the berry tissue first. Once the seeds have been obtained, they'll need to be scarified, and then put through a three to four month period of warm stratification and another three to four months of cold stratification to get them to sprout.

Step 3: Fermenting Tomatoes and Cucumber Plants

Fermenting tomato seeds
Fermenting tomato seeds

Not all seeds require this step. Passing certain ones, however, like those from the tomato and cucumber families of plants, through a fermentation process makes them sprout faster and increases their germination rate. Fermenting is done before cleaning for seeds that need this process.

Cut open the fruits open and squeeze the seed-containing juicy portion into a glass bottle. Add the same amount of water and stir well. Put tomato seeds aside in a warm place for two to four days. When following this process for the cucumber family of plants - squash, melons, gourds - give them approximately one to two days of fermentation.

Check for bubbles in the juice and a scum on top. When you see these signs of fermentation, add more water and shake well after closing the bottle. Pour out the liquid portion and repeat the process until the seeds are clean and the water is clear.

Step 4: Cleaning

Many wet seeds have lots of flesh attached to them.

Cleaning seeds
Cleaning seeds
  1. Stand them in a bowl of water for a while and then beat up the slush with a whisk to separate it from the seeds.
  2. Skim out most of the waste and pour out as much of the water as possible.
  3. Repeat the process until only seeds are remaining in the bowl.
  4. Wash them thoroughly until they are free of all the slime.

Some seeds that are floating should be discarded as well; they are the empty ones. As a general rule, good seeds sink and bad ones float. Exceptions are seeds such as that of lotus, which naturally depend on water currents to disperse them. The cleaned seeds should be drained in a fine sieve until maximum moisture is removed.

Spreading onion seed to dry at Canyon Bounty Farm in Nampa, ID
Spreading onion seed to dry

Step 5: Drying

Spread the seeds out in a single layer on a pane of glass or on ceramic plates. Dry them in shade and scrape them onto a paper. Dry seeds should not just feel dry to touch, but should make a dry rattling sound too.

Step 6: Storing

Store the dry seeds in tightly closed and labeled glass bottles. Make sure to add the date of collection and other details that will help you identify the seeds later.

Seed Storage and Viability

Moisture can spoil the seeds. Always house your seed collection in a cool and dry place. Most seeds stay viable until the next growing season. Their rate of germination will steadily decrease after that. But some seeds, such as beans and grains, remain viable for two to three years or more when stored well.

Have Fun

Collecting seeds is just plain fun and so rewarding when you actually see the fruit of your labor. Don't be discouraged if not all your seeds produce, just be sure to collect plenty to improve your odds.

How to Harvest Your Own Seeds