20 top seed and seed-starting faq’s

Juliet small paste tomatoes

Q. I have leftover seeds from last year. How long do seeds last, or remain viable?
Q. How do I do a germination test of leftover seeds?
Q. When do I start which seeds in my Zone?
Q. Can I grow my seedlings on the windowsill? Will I need grow lights?
Q. How many hours a day do I run my lights?
Q. What are heating mats or germination mats? Must I use one to get seeds to grow?
Q. What kind of soil do I start my seed in? Can I use regular potting soil, compost, or garden soil?
Q. I need a basic how-to on starting seeds.
Q. What seeds do I start outdoors, right in the ground?
Q. I am confused by claims of “organic” seed and other words like “sustainable” seed. Does it matter what I buy?
Q. Who sells organic seed? Where can I find it?
Q. What about the genetically modified or GMO seed that I hear so much about in the headlines?
Q. Where can I shop for good-quality seed; what are your favorite catalogs?
Q. How do you figure out what to buy in the seed catalogs?  So many beautiful choices!
Q. How do I grow tomatoes from seed?
Q. All my spinach and lettuce matured at once, then I had none. Why? What is succession sowing of seeds?
Q. What are some of the seeds you order for yourself, Margaret?
Q. Can I grow garlic from seed?
Q. Can I grow potatoes from seed?
Q. Can I grow asparagus from seed?
Q. Can I grow clematis from seed?

Q. I have leftover seeds from last year. How long do seeds last, or remain viable?

A. There is no hard-and-fast answer on how long leftover seeds last; every expert has a slightly different take, making memorization of any absolute rules impossible. Most seed will last a couple to several years—but there are disclaimers to even that general a statement.

As living things, seeds are perishable, particularly if not kept cool and dry (such as in a tightly sealed jar in the refrigerator or freezer). Humidity, in particular, is death to seeds.

Treated and pelletized seed will also have a different shelf life from seed in its natural state. The condition of the original crop the seed was harvested from will also, of course, affect how perishable it is.

Onion seed lasts just a year, everyone seems to say, with parsley and parsnips also very short-lived in storage. Muskmelons last about five years; watermelons slightly less. Corn about two, maybe three, and likewise for peas and beans.

I prepared a handy reference chart (above; details here) to viability ranges of vegetable seeds according to various experts.

The best way to be sure: Do a germination test. (Details also below.) But this is tricky when you bought some great heirloom pumpkin and there were just 20 seeds in the packet and now only half those remain, and also it’s only one part of the equation on seed health.

Germination tests predict viability (the ability to germinate), but they don’t accurately predict vigor—the seeds’ potential for uniform, fast germination and subsequent development in outdoor conditions, not the cozier, controlled conditions of a germination test. Life in the field isn’t the same as life wrapped in a piece of paper toweling in a plastic bag indoors on the kitchen counter, or in the special refrigerator unit of a seed-company testing lab (above).

“Seed vigor is a measure of the extent of damage that accumulates as viability declines,” says part of a class curriculum on seed biology at Ohio State University. “Eventually the seed dies, but first vigor declines gradually.” The important seed-vigor story.

As for germination assessment, if you don’t have many seeds left over to test: Make an educated guess based on what’s the date on that packet, and how carefully you cared for it the last year. Safest of all: the educated guess and a backup supply of anything where you might be caught short if the calculation proves wrong.

If it turns out you don’t need the new backup seed, you can always use it next year.
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Q. How do I do a germination test of leftover seeds?

A. Germination testing of leftover seeds would make a good science project for grade-school kids, and it can delight and inform big people, too. If you can count to 10, you can test last year’s seeds for viability, before wasting money on unnecessary replacements.

Gather a couple of zipper-lock plastic bags, sheets of paper towel (one per variety being tested), small plastic labels and an indelible marker. Count out 10 seeds of each kind being tested, place them in a row on a damp paper towel, and roll it up, with the label marked with the variety name rolled inside, too.

Put the whole thing in a plastic bag (you can put a number of these rolls into one large bag) and leave it in a warm place. Check it after a few days, and again after a week, and so on, and make certain things stay moist inside. Count the seeds that have germinated, and multiply that number by 10 to get the percentage of viability. If eight seeds are alive, your packet it approximately 80 percent viable; go ahead and use it. If only three germinated, you should re-order—or sow very heavily if you have a lot of seeds left, or only need a few plants. But remember (as above): viability isn’t the whole story; vigor is the other part of the equation.

More details on germination testing of seed.
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Q. When do I start which seeds in my Zone?

A. Depending what USDA hardiness zone you live in, and what crop you want to grow, you can calculate approximately when to start what based on the data in tools like these:

Remember that these calculators generally use years of average government weather data to offer approximate dates. Adjust if they first and last frost dates seem a little off; your local Cooperative Extension can help, or ask an experienced gardening neighbor to verify.
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Q. Can I grow my seedlings on the windowsill? Will I need grow lights?

A. Generally speaking, the light of a windowsill is not sufficient, nor does it come from overhead (to insure stocky plants instead of stringy ones that stretch and lean). And then there is the issue of drafts in the late-winter and early spring weeks when some seeds are started. So no, don’t use the windowsill, but instead create a seed-starting rig with lights.

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Q. How many hours a day do I run my lights?

A. Between 12 and 16 hours a day, with the lights suspended close to the tops of the seedlings (an inch or two to no more than four inches above them at any time, meaning you will need to adjust the level of the table or the lights as the plants grow). Again, you are trying to produce a stocky, balanced plant, not one that stretches for want of light. Use of a timer makes this foolproof.
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Q. What are heating mats or germination mats? Must I use one to get seeds to grow?

A. Many, or perhaps most, seeds like heat to germinate best. Special waterproof electric heat mats are available at most major catalogs that sell seeds (like Johnny’s, for instance, and are placed under the seedling trays after seed is sown during germination. The mats raise the temperature in the area inside the flat about 20 degrees above the room, or ambient, temperature. This is certainly more fuel-efficient than heating up a whole room hot enough to warm the tiny cells of soil to the desired degree, so mats are a great tool. Not essential, but helpful and efficient for germination.
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Q. What kind of soil do I start my seed in? Can I use regular potting soil, compost, or garden soil?

A. Use a mix labeled for seed starting or germination for best results. It will be fine-textured, having been screened to eliminate big bits, as many seeds are small. Oftentimes general-purpose potting soils (such as you’d use for houseplants or annuals in outdoor containers in summer) may include bark and other coarse-textured materials that aren’t great for encouraging seeds to push up through the surface.
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Q. I need a basic how-to on starting seeds.

A. Start with these posts: seed starting in words, and seed starting in a simple slideshow.
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Q. What seeds do I start outdoors, right in the ground?

A. Everyone differs on this; no rigid rules. Things I prefer to direct sow because it’s so easy include salad greens (lettuce, arugula and such); peas (as soon as the soil can be worked, about mid-March here); and spinach (either late fall for an extra-early crop, or very early spring); chard; broccoli raab; beets and other root crops; kales and collards; dill, and beans.

I like to direct sow pumpkins and squash and cucumbers, too, but the chipmunks often make off with the seed. And with the greens, there’s a tradeoff some years to direct-sowing, especially for me with the brassicas (the kale and collards), which can coincide sometimes with an upsurge in flea beetles, who eat tiny holes in things (they love arugula, too). Sometimes starting the plants indoors can outsmart the flea beetles, but growing them under a floating row cover will help, too. I never start peas or beans indoors; the rest I sometimes do, again, to cope with pests.
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Q. I am confused by claims of “organic” seed and other words like “sustainable” seed. Does it matter what I buy?

A. It makes a big difference environmentally, and also in what results you can expect to have in your garden. Unlike many vegetable crops we grow to eat—which are typically picked young and tender, and therefore grown for a shorter time—the same plant cultivated for a seed harvest must be grown to a much older age, requiring much more water, fertilizer, and chemical controls against pests and diseases.

Seed crops are coddled, and regulations on chemical usage when raising them is also looser than on growing the same vegetable for the food market.

Besides the “upstream” pollution and waste of resources this results in, it fails to do something else really important: It yields seed strains that “expect” this kind of pampering—not ones that are well-adapted to organic growing conditions in our home gardens, where we (hopefully!) don’t rush in with a chemical at every turn of events, or prop things up on synthetics instead of diligent care for our soil. More on that.

At a minimum:

  • Buy only from companies that say in their catalog or on their website that they took the Safe Seed Pledge, committing to not knowingly using or selling any genetically modified, or GM, seed. More than 100 companies have signed on.
  • Some skeptics ask, “But what does the pledge really mean?”–pointing out that the patented transgenic hybrids (often called GMOs), the dominant seed used in agriculture with crops such as corn and soybeans, are not listed for sale in garden catalogs. But here’s why I like seeing the Safe Seed Pledge: I expect a company who takes it will be able and willing and even proud to answer my other questions about where the seeds they sell were farmed, and how. Ask! (I also like seeing a company state that it tests its seed for possible contamination by pollen from genetically engineered crops–which is the way the unwanted genetics could get into a variety that the seller offered, believing it to be pure.)
  • Read the fine print. Any reputable vendor should freely express its point of view on GM seed, treated seed (that to which fungicide has been applied–say “no” to that, too, won’t you?) and generally how the seed is grown or sourced. More on that in this piece I wrote in 2013 in “The New York Times.”
  • That said: Many growers cannot make the certified-organic claim—whether because they have not yet met government guidelines, the cost of certification is too high, or they ideologically disagree with some aspect of the standards—but nevertheless follow sustainable practices and ethical land stewardship, and in fact are growing organically, if not certified as such. Like I said, read the fine print–a company should be proud to tell you the care it has gone to to find high-quality product for its customers.

My full article on this important topic, with links to companies that have taken the Safe Seed Pledge; organic seed companies; GMO information and more.
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Q. Who sells organic seed? Where can I find it?

A. This article includes many resources for buying seed produced in a sustainable or organic manner.
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Q. What about the genetically engineered or GMO seed that I hear so much about in the headlines?

A. I wrote about this in 2013, in “The New York Times.” I am no scientist, but here goes: GE (genetically engineered) hybrids have been created using biotechnology, in a laboratory. The genes of another less-closely-related organism than is possible with conventional hybridizing are inserted into the plant in question.

Transgenic hybrids are different from other hybrids. Hybrids can even occur in nature from cross-pollination. Manmade hybrids are deliberate crosses of two genetically distinct but pretty closely related parents (to breed in vigor or disease resistance or height/compact size or later harvest or whatever trait you’re seeking). Typically the two plants are from the same species…which is why they can hybridize, or “mate” so to speak. Not so with GE crops (often referred to as GMOs).

The technology to insert genes and create what are often referred to by critics as “Frankenplants” was developed in 1982, when scientists working for Monsanto were able to genetically modify a plant cell for the first time. It has since been applied to agricultural seed crops including canola, corn, soy, sugar beets and alfalfa (have I missed one?).

What results is often referred to as GMO (a genetically modified organism), but I think that in the science community they prefer to call the offspring “transgenic,” an even clearer term than GM/GMO.

Again: transgenic crops are the result of biotechnology — I guess we laypersons think of that as “gene splicing” — the insertion in the lab of genes from a more distantly related organism than nature would allow. So while hybrids have been made for a long time (think Gregor Mendel’s pea experiments in the 1860s onward) and can even be done in the garden by hand, genetic engineering is a different process. Individual genes are removed from the cell nucleus of one organism and spliced into the chromosomes of another…manipulating genes. We do not know the longterm effect of any of this experimentation: on us, on the food supply, on the diversity of the botanical genepool, on the environment.

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Q. Where can I shop for good-quality seed; what are your favorite catalogs?

A. My Resource Links page includes various garden catalogs under “Seeds”.

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Q. How do you figure out what to buy in the seed catalogs?  So many beautiful choices!

A. Before ordering, or even browsing around, I review my “seed catalog shopping rules” (video above) which are not so much rules as guidelines for how to figure out what I need, and how much. These steps may help you, too.
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Q. How do I grow tomatoes from seed?

A. I start tomatoes indoors for about 6 weeks before setting them into the garden a week or so after final frost here. So I start about April 15, and plant out at the end of May or early June. I strive for a stocky transplant of about 4 inches high and wide; bigger isn’t necessarily better. (By the way, that’s ‘Juliet,’ up top, a great tomato for sauce.)

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Q. All my spinach and lettuce matured at once, then I had none. Why? What is succession sowing of seeds?

A. When spring fades into summer, in particular, cool-season vegetables—the spinach and broccoli raab and various other once-succulent things—stretch up in protest, saying “No more!” How to achieve a continuing harvest with some simple succession-sowing tactics:

My mathematical equation starts on paper, like this:

1. Make a list of what you want more of (or a first crop of, if it’s a warm-season thing or if you simply didn’t plant an earlier crop).

2. Make a list of things that have gone by or will soon, to assess real estate that you can utilize. My list is here.

3. Compare the lists, and start making matchups. Examples:

  • Pea trellises might be a good place for pole beans (or other vining crops like squash or cukes)…but then I might want to plant fall peas. Hmmmm…which do I want more?
  • Sometimes I place my young tomatoes just alongside the peas, knowing I’ll rip the peas out a few weeks after the tomatoes go in, but before they need all the space. Those years, I yank the pea trellis and insert tomato cages.

4. Also look for marginal spaces you can cheat by a few inches—or a foot. You’d be surprised how much produce you can pack into beds if they contain well-loved soil rich in compost. For instance, between your tomatoes and the path, hanging over the edge even, why not put parsley, the next generation of beets and carrots, cilantro, salad greens, or even a row of bush beans? I do.

5. As you start calculating, also study a “succession sowing” chart for your area, perhaps from your cooperative extension’s website or an organic-farming association. Identify how long you can wait to sow what and still get a harvest by frost time. Here’s the chart I use.

6. Remember the basic “best practices” of vegetable-garden care to maximize yields:

  • Plant short rows every other week for a sustained but manageable supply of salads, greens, bush beans, cilantro. (The same repeat short-row sowing that stretches spring harvests can be repeated in later summer to get a long fall harvest, though sometimes different varieties of the same crops are more adapted to cooler months.)
  • Keep picking! Continual harvesting delays a plant’s instinct to “bolt” or set seed.
  • Weed to reduce competition for moisture, light and nutrients (asparagus, onions and garlic, in particular, really suffer with competition).
  • Remember which way the sun travels in summer, and don’t accidentally put someone who’ll be small on the shady side of someone who’ll be tall (unless it’s intentional, such as to shade summer salad).
  • Water deeply on a regular basis, drenching the entire root zone.  (Note: With a sprinkler, this takes many hours. Soaker hoses or drip emitters are more direct if properly placed in beds.)
  • There are more tips in the slideshow below (like hilling your potatoes!).

7. Waste not! Many “gone-by” greens (so long as they’re not positively woody) are tasty cooked.  Mustard or arugula you may have let stand a week too long to be salad material could serve up beautifully with a minute in the sauté pan.

The topic is covered in greater detail, including sowing timetables and various reference links, here.
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Q. What are some of the seeds you order for yourself, Margaret?

A. Here are some recent choices:

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Q. Can I grow garlic from seed?

A. Garlic is typically grown from bulbs (we call them cloves when we’re cooking with them), and planted in the fall, even in cold zones. It is harvested the next summer, then stored, with the biggest and best cloves saved for use as the “seed” to start the next crop in fall. Here’s the garlic-growing story.
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Q. Can I grow potatoes from seed?

A. The potato wouldn’t be the fourth-most-consumed food crop in the world (behind only wheat, corn, and rice) if it weren’t relatively easy to grow, but rather than starting from seed, we use “seed potatoes,” a smallish potato, or a wedge of a larger potato that was cut up to include some eyes on each chunk, then allowed to cure a few days in the air before planting. More on growing and storing potatoes.
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Q. Can I grow asparagus from seed?

A. Asparagus, a long-lived perennial, is normally grown from crowns (bare-root plants that are sold dormant in very early spring), not seed.  How to grow asparagus.
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Q. Can I grow clematis from seed?

A. Those crazy-looking fluffy seedheads of Clematis do indeed contain seed you can use, if you know how to determine when it’s ripe. Info here.
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no comments
February 18, 2011

comments

  1. Patrick's Garden says

    Great stuff Margaret for me and especially newbie gardeners. I agree the seed viability tests were recommended before the seed companies became so stingy with the amount of seeds in each packet..

    I’d like to see the same kind for cutflowers. I do hope all these hordes of new veggie gardeners will save one or two rows for cutflowers. I believe zinnias are a great choice.

    • says

      Love zinnias, too, Patrick. Nice to see you! I usually grow a block of zinnias and also have Nicotiana, which the hummingbirds love, self-sowing all about. Ah, thoughts of summer… :)

  2. boodely says

    I grew zinnias and sunflowers in with my tomatoes last year and it was so much fun to see the flower faces poking out of the tomato jungle, little landing platforms for butterflies.

    As soon as the snow lessens I will be harvesting my stash of parsnips, grown very successfully from 3-year-old seed! Figures.

  3. says

    I am proud to say that this year my garden shall grow with many seeds I saved last year. I made certain to plant only Heritage varietals and have just started my first tomato seedlings in my sunny window with last years seeds.
    The one thing that my time travel experiment has taught me is to cherish the past and also LEARN from it.
    I just found your blog and it seems lovely. I adore gardening and believe now that to learn it and continue to ‘grow’ with it, is very important for our world’s uncertain future.
    Perhaps when I return from 1957 I shall get your book and give it a read.

    • says

      Welcome, 50sga. “Cherish the last and learn from it” is a good motto, thank you. Hope to see you again soon in the here and now, tee hee, but frankly I love the old-fashioned varieties, too, so would be happy for living in another era in many ways as well.

  4. Ken York says

    When I was at a master gardening conference back in the late 80′s the Canadians were modifying tomatoes with genes from north atlantic haddock to be more cold tolerant. Then they sold them to the tomato industry in California.

  5. says

    I always plant a large area of mixed greens, turnips, kale, collards, in a fenced off section of my chicken pen. Any damaged roots or buggy tops get tossed over to my hens all winter long. I live in the deep south so fresh greens are mostly a winter time treat for us. When the plants do bolt as the weather warms I open up the pen and let the girls enjoy the whole patch.

    • says

      Nice to see you, Susan. Those are some lucky chickens. I would feed all my bits to a flock, too, but too many predators here (I live in a big state park/forest area…with everyone four-legged or winged who likes chickens!). Would love the eggs and the manure. Keep being tempted but I think I know better from the havoc farming neighbors have experienced. Sigh.

  6. says

    Yes, predators can be a major problem. Right now during the winter it is hawks I have to worry about. I use to have terrible problems with possums, and coons, but you know what is hard to believe? Since the coyote population has built up around here in the nearby woods, I have not had any more attacks on my flock and the coyotes haven’t bothered them either.
    One other trick we use to get certain seeds to sprout faster is to soak them overnite before planting them. Okra and bean seeds will sprout much faster if they are soaked.

    • says

      Hi, Lysa. Sounds like you have plant for a fruit farm! :) Don’t know where you are located but the kiwi will have to be one that’s hardy in your zone. Whatever kiwi you grow, there are separate male and female plants, so to get fruit someday you’ll need both. Oregon State has a good pdf about growing kiwi (again, I don’t know where you are located so the ones that will grow there may not grow for you). The ones in the market tend to be from much warmer climates than mine, for instance – I can only grow the so-called “hardy” kiwis, not the big fuzzy ones from the supermarket here (but I am Zone 5).

  7. jody currin says

    We have started the community garden seeds in the greenhouse, they are coming up nicely. I have been working with a few of the FFA students and most of the seeds came from Seeds of Change their sow a million seeds program in which a few were dated, but they are producing wonderfully. I think the trick is their packaging which is also very pretty to display. Thank you Ms. Margaret for all of the great ideas and tips. Your newest book is on my reading chair and i am enjoying it very much, it was a birthday present.

  8. says

    I really want to learn how to grow veggies this year so hopefully I will gain access to a community garden (throught the City). I am excited to join their first meeting tomorrow night. Wish me luck as I have zip zero nada veggie gardening experience.

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