Since I was able to purchase NON-GMO seed, I'd like to harvest seed from my vegetable garden this year. How do you tell when the seed is ready for harvest? Lettuce, cauliflower, cabbage, celery, beets, squash?

  • One year later!! Did you have any success saving seeds this past year?
    – J. Musser
    Sep 21, 2015 at 21:28

2 Answers 2


Why are heirloom varieties best for saving seed? They aren't hybridized, so their offspring will be very similar genetically, to the original stock, if good techniques are implemented.

So, for the basic answer:

We'll first go into pollination. There are:

  • Self-pollinated plants

  • Insect-pollinated plants

  • wind pollinated plants

Let's look at self pollinated plants first. These have functional male and female parts within the same flower (or have both flower types on the same plant). This makes setting seed easy, but some can cross-pollinated by insects as well, which means you'll have to use isolation techniques with them.

Insect pollinated plants, on the other hand, always require varietal purity techniques in order to maintain a specific variety. There are many insects that pollinate plants, but the most common efficient one is the honeybee. These are great, because they will only visit one type of flower during a trip, so they are far less random than bumblebees, sweat bees, isolated bees, etc. Moths and butterflies, though they visit flowers often, are not efficient at pollination. Wasps don't have the type of hair to transfer pollen well, so they aren't good, either. Flies, though random, will pollinate flowers that have open, exposed nectaries, such as various individuals in the Umbelliferae and Brassicaceae families.

Wind pollinated plants (such as corn or spinach) are easy to keep pure, if you live alone. All they need is isolation.

Maintaining Varietal Purity

  • distance isolation: This is the technique of growing the seed plants far enough from potential pollinator plants (either wind- or insect-pollinated) that the pollination is almost pure. The distances change from plant to plant.

  • time isolation: This is the technique of sowing and raising plants at a far enough time from the potential pollinators that the seed remains almost pure. The times, of course, vary from plant to plant.

  • mechanical isolation: This is the use of a physical barrier to keep the plants from being pollinated by other strains. There are a few ways of doing this.

    • Bagging: This is used to isolate only the flowering portion of a plant, especially where only a small amount of seeds are needed. Like on tomatoes, you can cover an individual cluster with a bag, so that the only pollination is self-pollination. Paper bags are the most common. Never use plastic.

    • Caging: This is often a wood, plastic, pvc or wire frame, covered in screening or lightweight row cloth.

      • Alternate day caging: This is to maintain purity when raising two varieties together. You plant the two varieties together, and when they start flowering, cage only one variety. The insects pollinate the others all day. That night switch the cages over to the other variety, and the originally caged plants get pollinated the next day. This is used for insect pollinated plants.

      • Caging with introduced pollinators: This is using rapped or newly emerged pollinators (flies or bees) to pollinate the plants inside the cages. They need to be large enough to allow flying room around the plant.

  • Hand pollination: This is often used for plants that are insect or wind pollinated, to maintain pure seed. This is often done in conjunction with caging, for plants that are naturally insect pollinated.

Selection and Population Size

Vegetable seeds are constantly changing (slowly) due to either environmental factors or genetic factors, and you have to learn how to maintain a variety using certain techniques. You have to learn to look at the entire plant, and develop for specific traits. Characteristics to consider will include:

  • earliness
  • disease resistance
  • insect resistance
  • drought resistance
  • stockiness
  • vigor
  • color
  • lateness to bolt
  • hardiness
  • uniformity
  • trueness to type
  • flavor
  • overall health

How is this accomplished? Each year, seed savers must grow a good amount of each plant they want to save. The more plants the better, to maintain genetic diversity, and plant vigor. Once the plants are planted, watch the new plants. Cull any which differ from the original plants. Like being noticeably smaller, a different shape, bug bitten, etc. Every off-type is to be removed.

How do you tell when the seed is ready for harvest? Lettuce, cauliflower, cabbage, celery, beets, squash?

  • Lettuce seeds ripen irregularly and are ready to harvest from 12-24 days after flowering. The seeds should be harvested daily during that time, by shaking the seedheads into a large grocery bag and storing in a dry place in between.

  • Cauliflower is usually a biennial, and requires vernalization in order to flower. This means that if the plants are in an area where is gets colder than 28 degrees F., the plants will need to be dug up and stored overwinter at between 32 and 40 degrees F., at 90-95% relative humidity, and planted out again in the spring. Cut the stalks when the pods have turned brown, but before they shatter. Hang in a dry place to continue drying, and tie a paper bag on the end, to catch the seeds.

  • Cabbage is the same as cauliflower, except that when planted out in spring, you need to cut a shallow 'X' in the middle of the cabbage, to allow the stalk to emerge. Otherwise, see the cauliflower section.

  • Same as for the brassicas, celery needs to be overwintered and replanted in the spring. Celery doesn't like being disturbed, rootwise, so dig them carefully. They will then grow a seed stalk. Celery seed stalks are comprised of several umbels, some of which ripen before others. It is best to harvest the umbels one at a time, as they mature, but before they shatter.

  • Beets These are also biennial, and must be dug and stored in damp sand (in a 90-95% relative humidity environment) overwinter in most areas. Harvest when the seed clusters on the 4' stalk have turned light brown. Once the stalks are completely dry, thresh them with a flail, and winnow to remove chaff (I have used the wind method).

  • Squash Harvest when completely ripe, and let them sit at least a month before removing the seed. Pick the seed from the pulp, and rinse in a colander, removing all debris. Drain and dry.

Seed saving is a very time-consuming and involved process, which is why it has become less and less common over the past years. There are still many interested in the process, and you can find tutorials and videos online, demonstrating how to do any of the numerous tasks you will need to accomplish. It is an art form, and so many people find it more convenient to simply buy new seeds each year.

The book that has helped me most, and I highly recommend to anyone with an interest in this topic (also my main reference for this answer), is 'Seed to Seed' by Suzanne Ashworth.

  • 1
    If you need expansion on any point, let me know.
    – J. Musser
    Sep 22, 2014 at 19:22
  • 1
    Oh my goodness! What a great answer!! WELL! Gotta start out planning to harvest seed. This is so well done, J. But gotta learn how to do this. I don't expect to always have non-gmo seed available. Thank you so very much!
    – stormy
    Sep 22, 2014 at 23:52
  • @stormy most vegetable seeds are non-gmo. As itsmatt says, hybrid and gmo are different. Again, if you want me to expand on any point, I'd be glad to, and if you have any new questions, ask some new ones.
    – J. Musser
    Sep 23, 2014 at 0:36
  • Absolutely...but how do you know most seeds we buy at the store are Non-GMO? The only way I can be kinda assured is if the package says Non-GMO. They were tough to find this last season.
    – stormy
    Sep 23, 2014 at 1:54
  • 1
    @stormy I believe non-commercial varieties of vegetables have to be labeled as GMO if they are. Your basic seed catalogs don't usually have GMO seed for sale. I know Jung, for one, does their best to never sell gmo seeds.
    – J. Musser
    Sep 23, 2014 at 1:56

I'm going to assume that you're wanting to save open pollinated seeds. There's a difference between GMO, "hybrid" and "open pollinated" seeds. While you can save hybrid seeds, you're getting an intentionally cross-pollinated plant seed initially but if you save seeds from that, you'll not get the same plant from those seeds. But you can save them if you want.

I don't grow beets. Never met a beet I liked. =)

I don't grow celery but it's a biennial. Can't speak to saving either of those.

I imagine someone else can talk about those two.

Lettuces are pretty easy. You might need to concern yourself with cross-pollination - there are techniques for this - row covers, etc. but more to the question you asked, they'll bolt when it gets too warm, create a flower and then after it blooms it's maybe 2-3 weeks before the seeds are ready to harvest. There's some wiggle room there.

For squash seed saving I let the squash fruit ripen past the point where I'd harvest them to actually eat. The fruit gets a bit harder at this point and then the seeds are good to go. Honestly, I'd say I give them a week past the point where I'd harvest to eat. I suppose you could wait longer but I never do. I cut the squash open, scrape out the seed and rinse them off in a colander. I do the same thing with pumpkin seeds. I run water over then and move them around in the colander to remove the pulp and stuff off of them and then I spread them out to dry. Very easy to save them.

Cauliflower is a brassica and so is a biennial plant - it seeds in the second year, like carrots do. I'm assuming you already knew this but anyway. They get tall - 3 feet or more - and when those pods brown up, they're ready. They need to overwinter safely though for year two. Folks in colder climates need to save them from freezing hard - digging them up and storing them until spring is common.

Cabbage is a brassica too and a biennial. Similar thing going here. Note, however, that brassicas will readily cross-pollinate and so unless you've isolated them well, you run the risk of your brassicas cross-pollinating and producing some cabbage/cauliflower cross. Interesting, but not likely what you want.

  • I was afraid of this cross-pollination thing...arghhhh! I'll probably try collecting a few seeds to try next year otherwise it is back to the seed catalogs! Thanks Matt!
    – stormy
    Sep 22, 2014 at 18:23
  • Have you tried beet greens? They are my favorite part even better than spinach! Grin!
    – stormy
    Sep 22, 2014 at 18:24

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