Kenwood Press

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Over the Garden Fence: 04/15/2013

Timing is important when starting your vegetable garden

There are three ways to get your vegetable garden started this spring: first is sowing seed directly in the garden; second is sowing seed indoors, in a greenhouse or kitchen window, and later transplanting your seedlings into the garden; third is purchasing seedlings at the garden center and then transplanting them into the garden.

Sowing your own seed gives you a wealth of varieties to choose from; there are hundreds of vegetable seed varieties available at garden centers, hardware stores, and online. When you choose vegetable starts or seedlings purchased at the garden center, you are limited to the varieties a grower has chosen for you.

Know your growing season

Whichever route you choose, a key factor in vegetable gardening success is knowing when your growing season begins and when it ends. The growing season wherever you live is determined by the last frost in spring and the first frost in autumn.

The average date of the last frost in the Sonoma Valley is April 10 and average first frost is December 6 (the average is determined by decades of government weather records). Of course, Mother Nature knows little about averages; if you have been keeping track, you know the actual last frost in the Sonoma Valley in each of the past five years has come in mid-May. Our growing season is about 280 days long.

Cool-season and warm-season crops: hardy to tender

Sowing seed and setting out transplants can be a risky business. There are two types of annual vegetables - those that thrive in cool weather and those that thrive in warm weather. Sowing or transplanting too early - before the last freeze - can mean crop failure for many crops.

When is it safe to sow seed in the open garden; how much chill can a crop take? Here is a quick guide to vegetables that can take a frost - called “very-hardy crops,” and those that will absolutely be damaged or killed by frost - called “tender crops and very tender crops” as well as those crops in between.

  • Very Hardy crops (sow in the garden as early as 5 to 7 weeks before the last frost): dill, garlic, leeks, onions, peas, shallots, and spinach. 
  • Hardy crops (sow in the garden 2 to 3 weeks before the last frost): chervil, coriander, lettuce, mustard, parsley, and turnip greens. 
  • Semi-hardy crops (sow in the garden 1 to 2 weeks before the last frost): beets, broccoli, Brussels sprouts, carrots, cabbage, cauliflower, chard, kale, kohlrabi, parsnips, potatoes, and radishes. 
  • Tender crops (sow in the garden on or just after the last frost): beans, corn, pumpkin, summer squash, winter squash, and zucchini. 
  • Very tender crops (sow 2 to 3 weeks after the last frost): cantaloupe, cucumber, lima beans, eggplant, peppers, sweet potatoes, tomatoes, and water melon. 

Starting tender crops indoors

Because outdoor conditions can be so unpredictable, very tender crops are almost always best started indoors where the temperature is controlled. Crops best started indoors and later set in the garden as transplants are cantaloupe, eggplant, peppers, and tomatoes. Tender vegetable starts are best transplanted to the garden at about 6 to 8 weeks old.

Early April is a good time to start very tender crops indoors. In 6 to 8 weeks, your garden will have come past both the average last frost date and in all likelihood the actual last frost date for this year.

The easiest way to start seed indoors is to find a warm spot near a south-facing window that gets plenty of sunlight. Most vegetable seeds require a consistent soil temperature of 70°F for germination; that's near enough the temperature you keep the house. Once seeds are up, seedlings want sunlight to thrive. Turn your seed-starting trays or pots daily to make sure young seedlings don't stretch one way or the other to get light. Keep the seed-starting medium or soil evenly moist - not too wet and never dry. Your seedlings will be ready for transplanting in about 6 weeks.

Vegetable garden tasks for April

  • Add aged compost and aged manure to vegetable garden planting beds if you haven't already. Aged steer manure is the best manure choice this close to planting time; chicken manure is rich in nitrogen (which can burn tender plant roots) and is best spread across planting beds in late winter, a couple of months before you plant. 
  • Make sure your irrigation system is ready; check drip lines and replace soaker hoses before the weather turns warm. 
  • Have tomato cages and plant stakes at the ready; the best time to set supports in place is at planting time. Set tomato cages in place as soon as you have transplanted out tomato and pepper seedlings. These crops will need support in a couple of months' time. If you set supports in place now you won't risk damaging growing roots later. 
  • If you want to get a fast start to the growing season, place black plastic sheeting over your growing beds now. Two to four weeks of solar heat will have those beds toasty and ready for seeds and seedlings at planting time.

Steve Albert is the author of The Kitchen Garden Grower’s Guide available at He teaches in the landscape design program at the U.C. Berkeley Extension. He lives in Oakmont.


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