Starting Plants from Seed

_lio/stock.xchngThere are many reasons a home gardener chooses to start plants from seed rather than buying transplants, according to Megan Jensen, an organic greenhouse manager. “There's something special about seeing the entire process from seeding to germination, through growth and transplanting,” she says. 

In addition, seeds are more economical. For instance, a couple of dollars will buy you enough seeds to grow tomatoes to feed a small army, while for the same price you can buy about one transplant, or about one half of one heirloom tomato from the supermarket.

Seeds also offer more variety. Seed catalogs provide a broader range of choices than whatever your local garden center has in stock. Also, some crops require sowing directly in the soil because their roots do not deal well with being transplanted. These include carrots, corn, parsnips, beans, and peas. “Summer squash and cucumbers don't like having their roots disturbed either, but I've had luck with seeding them in flats and transplanting them early, before they grow more than one set of true leaves,” Ms. Jensen advises.  

A Time to Sow

The time to start your seeds depends on a number of factors. Some seeds, like the California poppy, are best sown in fall or winter for spring growth. Some seeds require cold stratification, which means they need a period of coldness before they sprout. You can either sow these seeds during the cold season, or in a warmer climate you can simulate this by mixing your seeds with damp peat moss in a plastic bag and storing in the refrigerator until the seeds start to sprout. At that point, remove them and plant in soil.

Most vegetable seeds are best sown in the spring after the last chance of frost. If you live in USDA plant hardiness zones 2-6, this means it's often best to start seeds indoors a few weeks before the last frost date so that seeds have a head-start on the shorter growing season. However, it is not necessary and many crops, like lettuces, radishes, beans, and winter squash will do just fine sown in May or June, or even later. “Next week I'm seeding winter squash, a second round of beets, and some head lettuce,” says Ms. Jensen, who works in zone 6.

The Right Seeds

Ms. Jensen prefers to buy her seeds “from small seed companies like Baker Creek Heirloom seeds or Seedsavers Exchange, where you know that the seeds are non-hybrid and non-GMO. Hybrid seeds will produce plants whose seeds will produce plants that are not a true replica of their parent, making it impossible to save seed from them.”

Make sure you acquire viable seeds. They should not have been stored for too long or stored in humid or hot conditions. Of course, some seeds have remained viable after storage for thousands of years, but not all seeds hold up that well and it takes ideal conditions to achieve that kind of preservation.

Most seeds of garden annuals can remain viable for 2-3 years stored in a dark, dry, cool location. Storage time can be increased five-fold through storing seeds in a freezer. If you're using old seeds of questionable viability, you can take a sample and pre-sprout them by laying a damp paper towel in a plastic container, laying seeds, and putting the lid on it. Keep it in a warm place and check the seeds daily and add water if necessary to maintain moisture.

If fewer than half sprout, you should use newer seeds. If below 85 percent sprout, sow them more thickly. Pre-sprouting can also be used as a part of a regular gardening strategy. Tomatoes and peppers are particularly good for this method. Once the seeds sprout, transfer them to flats or to your garden.  

Starting Outdoors

For many of you, your last spring frost date has just passed or is quickly approaching, which means it is time to get ready to sow outdoors. Some great crops to sow right now or in the coming weeks are beans (including lima and soy), peanuts, cauliflower, cucumber, summer and winter squash, sweet corn, muskmelon, watermelon, basil, summer savory, and sweet marjoram.

In zones 9/10, most gardeners seeded their gardens back in March and April (some are already producing tomatoes!). Even so, succession planting will keep your garden producing food at a rate you can handle throughout the season.

When you sow outdoors, moisten the soil (which should be prepared for whatever you plan to grow) and sow about two to three times the amount of seeds as plants you plan to grow. Some plants, like cucumbers and watermelons, should be grown in mounds, while others, like eggplants or corn, should be grown in rows. As far as seed depth, Ms. Jensen suggests, “The rule of thumb for planting depth is to plant seeds twice as deep as the seed is tall.”

Keep the soil moist. “When first seeded, plants need a good watering in. The combination of dark and water tell the seeds that it's time to wake up and start growing.”

In very hot or windy climates, it can be difficult to maintain moisture over very small seeds. One strategy is to sow, water, then cover with a board or fabric and leave for a few days. Check again, and once the seeds are sprouting, remove the cover. Water used for watering should not be too hot. Sometimes on hot days it is necessary to let the hose run a little bit to push the very hot water, which will kill crops, out first.

Choose Wisely

A general gardening tip is to choose plants you already enjoy eating. But some plants, like strawberries, are difficult to start from seed. “Parsley is notoriously hard to start from seed, the germination rate is very low. Rosemary is also difficult,” says Ms. Jensen.

Whatever you choose to sow, keep a written record of what worked and didn't work for you. This will help you avoid repeating your mistakes, and will help increase your future success.

Updated November 25, 2018.

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