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Seed Starting with Mobee

Martha Stewart Living Television

 Starting plants from seed is an inexpensive way to diversify and expand your garden and grow many plants that are available only as seeds. Mobee Weinstein, a horticulturist at the New York Botanical Garden in the Bronx, shows some of her techniques for propagating plants from seed.

Make sure you begin with clean, sterilized pots. To sterilize terra-cotta pots, soak them for at least an hour in a sink or large bucket filled with a solution of 1 part bleach to 10 parts water. Wearing rubber gloves, scrub the pots inside and out with a scouring pad or stiff brush, and rinse well. (Let pots dry completely before you store them.)

For the potting mix, Mobee recommends a sterile well-aerated commercial soilless mix composed mostly of peat and vermiculite. Spritz the medium with water before working with it, if necessary, until it feels damp, yet still fluffy, to the touch.

Fill each pot to the top with potting mix, then level off with a stake or ruler. Firm the mix gently with your hand, but don't smash it down, because you don't want to force out all the air. Mobee's rule of thumb is to plant seeds two to three times as deep as the seed is wide -- for example, if a seed is a 1/4 inch wide, plant it a 1/2 inch to 3/4 inch deep in the growing medium. Plant a number of seeds in each small pot, and separate the seedlings later. Some seeds are so fine they don't need to be buried at all; just sprinkle them on top of the medium. To make fine seeds easier to plant, combine them with a bit of sand or some granules of gelatin. Some fine seeds are available in pelleted form, which means they are coated to make them larger and easier to handle.

As soon as you've sown seeds in a pot, label it precisely with the name of the plant and the date sown. This label will help you to track the days it takes a seed to germinate and will be useful for recording the information in a gardening journal.

Next, water the pots without disturbing the seeds by partially filling a pan or plastic bin with water and floating the pots in it until the surface of the growth medium appears moist -- a technique called bottom watering. Cover the pots with plastic or glass (in effect, turning each pot into a miniature greenhouse); cover with dark paper or newspaper as well if your seeds need a period of darkness to germinate. Seeds that need to be buried, as opposed to seeds so fine they are sprinkled on the surface of the soil, generally need this period of darkness.

Most seeds need warm temperatures to germinate. Provide your pots with a source of bottom heat. Use commercial heat pads, or place them on top of a warm appliance such as a refrigerator. Check your seeds at least twice a day. Once you see the first seed in each pot begin to sprout, remove the glass or plastic cover and any paper from the top, take pots off the heat source, and move them to full light.

When the seedlings grow their first true leaves, separate and transplant them. Slide the soil mass out of the pot, and drop it a few times on the table in front of you to loosen it; surprisingly this technique does less damage to delicate seedlings than separating them with your fingers. Use a pencil to tease the seedlings apart, then pick up each one very gently by the leaves. Make a small hole in the soil of another small pot with a stake or a pencil, then place the seedling in it. Firm the soil gently around it, then water it from the bottom as before.