When should you plant seeds and seedlings outside?

April 14, 2010 at 3:29 PM Leave a comment

John Scheepers Kitchen Garden Seeds
When should you plant seeds and seedlings outside?

We’re having absolutely glorious spring days here in Northwest Connecticut this week. Characteristic spring night temperatures dip into frost warnings now and again, despite the record-setting summer heat that we had just a week ago.

For horticultural zones 3 through 6, a good part of the United States, now is the time to start vegetable, herb and flower seedlings indoors. Most seedlings should not be planted until after “the last frost date”~the safe start of the real summer gardening season, when killing or “stunting” night frosts are no longer expected. If tender seedlings are planted in the garden too early, even though there may have been a record-setting heat wave previously, seedlings can become stunted and fail to thrive due to frosty night temperatures. If you plant a seedling outside too early, your plants may never catch up to your neighbor’s planted weeks later, due to the fact that your seedlings were hit by a spring frost for just one or two nights.

If you don’t know your “last frost date”, that magical gardening moment, check the National Weather Service: it lists each state’s last (and first fall) frost dates by major city, so you can figure out when to plant your seedlings outside. After the last expected frost date, it is also safe to direct sow Beans and Sweet Corn into the garden. Two weeks after the last frost date, it is also safe to direct sow Cucumbers, Squash, Melons and Pumpkins outside~they like to germinate in warmer soil. (That is really what we call magic: how such big, vigorous plants and vegetables come out of such little seeds with so little human effort.)

If you haven’t ordered your seeds yet, we encourage you to think of your kitchen garden in two parts: the start-indoors-first part, and the easy direct-sow-outdoors part. There are a number of cold hardy vegetables that may be direct sown now~regardless of your last frost date. These include Spinach, Peas, Salad Greens, Lettuce, Asian Greens, Swiss Chard, Radishes, Beets and Carrots ~all varieties that can handle frosty night temps. You can tell if your soil is “ready” by taking a handful: if it crumbles freely, the garden is ready to be worked! You can also plant Shallots, Garlic, Onions and Potatoes in early spring, prior to the last frost date.

USDA             Last Frost

Hardiness       Date

Zone 1             Mid June

Zone 2             Early June

Zone 3             Late May

Zone 4             Mid – Late May

Zone 5             Mid May

Zone 6             Early May

Zone 7             Mid April

Zone 8             Mid March

Zone 9             Mid Feb.

If you are about to plant your new seedlings outside, be sure to harden off them off first, by gradually placing them outside for incrementally longer periods of time over the course of a week to ten days.

The Do’s and Don’ts of Seed Starting

The best way to grow a green thumb is just to plant a garden each year and learn from your mistakes. But an old gardener’s tips can sometimes steer you away from failure. Here are the ones I go by:

1. Read the seed packet and obey its directions. If it says to start a vegetable ahead indoors 6 to 8 weeks before the last likely frost, do that. Note specific directions such as covering the seeds lightly, or not at all. Other seeds will be sown directly in the garden at the seed packet’s recommended time.

2. Use a good-quality, fine-textured, sterile soil-less mix for germinating indoor seeds, to avoid damping off.

3. Large seeds can go directly into cells or pots, a few in each, then thinned. But most seeds are tiny and are sown in small trays or flats to start. Then as soon as they germinate, lift them carefully and plant them individually in cell packs or pots. The younger they are when you do this, the better they will grow.

4. Good light is the most important, and often the most difficult thing to provide. Windowsills never seem to be sunny enough, and dimly-lit plants become tall and spindly. A set of broad-spectrum florescent lights suspended right above the seedlings gives great illumination~plus some heat. The lights under your kitchen counter might work if you install full-spectrum bulbs. Raise your flats closer to them (4” to 5”) with some bricks~or fat cookbooks.

5. Harden off your transplants progressively by putting them outside for increasing periods of time on nice days, but don’t rush them into the ground. Especially if they’re warm-weather crops like tomatoes. Plants set out later will quickly catch up to early-planted, shivering ones.

6. If you use peat pots for your transplants, tear off the rims and slash the sides. Handy as these are, they are actually quite hard for roots to penetrate.

7. Keep your leftover seeds in a cool, dry place. With many you can sow several times throughout the season for a steady supply of a favorite crop.

A Little Tip From Barbara Damrosch


Entry filed under: Green Information, Nature Notes, Our Gardens.

BHG publishes its “Best Perennials for your Yard” list Kitty Steals Gardening Gloves!

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