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Jessica Walliser

Tomatoes a great choice to start from seed

Jessica Walliser
| Thursday, March 1, 2018, 8:55 p.m.
Gather seed-starting equipment and get to gardening.
Jessica Walliser
Gather seed-starting equipment and get to gardening.
Seedlings get an early start under a grow light.
Jessica Walliser
Seedlings get an early start under a grow light.

Question: I would like to grow some tomatoes from seed this year. Is it too early to start them? Are there any special tricks I should know?

Answer: Starting tomatoes from seed opens up a whole new world to gardeners. While many of our local nurseries offer lots of different tomato varieties as transplants, there are more varieties of tomatoes than they could ever grow. If you want to grow an unusual tomato or some old-fashioned heirloom, you'll almost always need to grow it from seed. But even if you want to grow “normal” tomatoes, it's still fun and incredibly cost-effective to grow them from seed.

Thankfully, tomatoes are one of the easiest plants to grow from seed. The biggest mistake I see gardeners make when it comes to this job is starting the seeds too early. Here in Pennsylvania, tomato seeds should be sown about six weeks before our last expected spring frost. Our last frost date is typically around mid-May, which means tomato seeds shouldn't be sown until the first week of April.

Starting tomato seeds too early can lead to all kinds of issues, especially for home gardeners who often don't have enough light or room to accommodate fast-growing tomato plants. Wait until early April, and then follow these guidelines for growing tomatoes from seed.

First, gather your tools. You'll need a bag of sterile, seed-starting potting mix. Don't skimp on the potting mix; you get what you pay for. While you're at the nursery, you should also get a seed-starting nursery flat, some plastic plant 6-packs or small plastic pots, a handful of plastic plant markers and a seedling heat mat. Heat mats are important when starting seeds for warm-season crops like tomatoes, peppers, basil and eggplants. When placed underneath the seeding flat, it warms the soil from below, speeding germination and improving the percentage of seeds that germinate. The same seedling heat mat can be used for many, many years.

When seed-planting time arrives, fill the seed-starting nursery flat with potting mix to one-half inch below the flat's upper rim. Tamp the flat on a hard surface to settle the soil and knock out any air pockets. Then, use your finger or a pencil to make a series of rows of small holes in the seeding tray, each hole about 14 inch deep and spaced about 12 inch apart. Drop one tomato seed into each hole then sprinkle a little more potting mix over the seeds until they're covered.

Label the seed rows with plant markers so you remember which variety is planted where. Then, water the seeded flat well, using a soft, gentle hose nozzle or watering can. Allow the flat to drain thoroughly before placing it on the seedling heat mat and plugging it in.

Cover the top of the seeded flat with a sheet of clear plastic (I use dry cleaning bags). Water as necessary to keep the seeding flat consistently moist. As soon as the seeds germinate, remove the sheet of plastic and turn off the seedling heat mat.

Your flat of tomato seedlings should be placed under grow lights for 18-20 hours per day so that the bulbs are 2 to 3 inches above the top of the flat. As the plants grow, the lights should be raised so they consistently remain that same distance above the tops of the seedlings. If you don't have a grow light, you can use inexpensive fluorescent shop lights instead.

Alternatively, you can put the seeded flats in a bright windowsill, but the resulting seedlings may become leggy as they stretch for more light. If a windowsill is your only lighting option, be sure to turn the flat one-quarter turn every day to keep the seedling growth even.

When your seedlings develop their first set of true leaves, it's time to transplant them. Fill the small pots or plastic nursery six-packs you bought with new sterile potting mix. Carefully lift the tomato seedlings out of the seeding flat, separate them, and place one plant per pot or six-pack compartment. Bury the seedling deeply so that the lowest leaves sit just above the surface of the soil. This encourages good root production on tomatoes and keeps the seedlings stocky and strong.

Continue watering your tomato seedlings as necessary and raise the lights whenever you need to. Fertilize every other week with a diluted liquid organic fertilizer.

A week before you're ready to move the transplants out into the garden, begin to gradually acclimate them to outdoor conditions by moving the plants outdoors for a few hours per day. Start in a shady spot, and each day expose them to more sun and leave them out for a longer period of time until they're outside in full sun, both day and night. Only after this hardening-off process are your tomato seedlings ready to be planted into the garden.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is Send your gardening or landscaping questions to or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.

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