Growing Tomatoes from Seed
Growing tomatoes from seed indoors rather than sowing directly into the garden has real advantages--even if you live in a region with a long growing season and plenty of warmth! That's because you can better control the growing conditions: the soil, the lighting, and the containers. Best of all, you have a much greater choice of varieties and have complete control over all the tomato plant growing stages. It isn't complicated, and saves you money besides.
Sterile Soil for Tomatoes
Growing Tomatoes from Seed
Although tomato seeds can be started in just about any soil, I recommend you don't use regular soil from your garden. You'll minimize the chance of losing your seedlings to disease if you use sterile soil for growing tomatoes from seed. If you've seen a fuzzy white fungus on potting soil, it is probably damping-off disease--a term for the various fungi that can cause the seedling stems to rot away at the base. To help prevent damping-off, I'd really encourage you to use a sterile soil mix.
Soil-less mix
A lightweight artificial soil mix like Jiffy-Mix (which is made from sphagnum peat moss and perlite) is ideal for starting seeds indoors. Why? Because it is sterile, free of weed seeds, and doesn't compact like regular soil. The problem with compacted soil is it can inhibit root growth of your seedlings. You can make your own Peat-Lite mix by combining 50 percent vermiculite or perlite with 50 percent fine sphagnum peat. You could also stretch your budget by adding one-third sterilized soil to the mix. Regular garden soil can be sterilized by heating. Take good, slightly moist garden soil and pasteurize it by spreading it on a pan and baking in the oven at 250 degrees. The soil should remain at 140 degrees for at least 30 minutes so having a thermometer is handy. It can be a bit smelly, but it works!
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Peat pellets and soil blocks
An alternative to growing tomatoes from seed in a soil-less mix is to start your seeds in pre-formed peat pellets. It's a slightly more expensive alternative but very convenient. After soaking, the peat pellets expand into small soil containers that can later be planted directly into a pot or garden. Or you can make your own soil blocks by investing in a soil blocking tool. This is a neat way to make your own two-inch soil blocks for growing tomatoes from seed. Use seed starting mix or potting soil to make the blocks.
Seed Trays/Flats
You can start seeds in any container as long as it has drainage. The containers, whether bottoms of waxed milk cartons, paper cups, seed trays or individual containers, should be about two to three inches deep. I prefer to use seed flats, which are plastic trays molded into individual cells--one per seedling after thinning. Many of the available seed flats you'll find include a clear plastic cover for the purpose of keeping the soil from drying out. The best seed trays are insulated with built-in water reservoirs and capillary matting. Regular trays or any flat container will work, but dry out more quickly than plastic covered trays.
Labels
If you're growing tomatoes from seed using more than one variety don't forget to insert labels next to each tomato variety. If some do better than others, you'll want to know which were the successful ones! Note the variety and the planting date on the label. I like to use clear plastic three- or four-inch labels to avoid shadows, or white labels like those shown. This package comes with a special marking pencil. You can also use an industrial Sharpie or other permanent marking pen that won't fade in the sun.
10 Steps to Successfully Growing Tomatoes from Seed
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Fill a container with sterile soil mix within one-half inch of the rim.
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Thoroughly water the soil-less mix in the container and allow it to drain.
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Tamp down the soil lightly to firm it with your hand or a board.
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Place two or three seeds in each container or cell to be thinned later to one plant.
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Carefully sprinkle one-quarter inch of soil-less mix evenly on the surface and tamp down to ensure good contact between seed and soil.
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Using lukewarm water, spray or gently water the soil surface until thoroughly wetted and fill the water reservoirs if you have them.
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Cover the trays or containers with the plastic lid, plastic wrap, glass or newspaper but don't allow the cover to rest on the soil surface.
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Place the seed container in a location where the temperature is 75 to 85 degrees F for fastest germination. A soil thermometer is handy for this. If your location is too cool you can place the tray on top of a water heater or refrigerator. I use an electric seed-propagation mat, which is a heated rubber mat which I place directly under the tray. Another option to warm the containers from below is to use heat tape or cables which you can buy at garden supply stores or online.
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Check daily until the seeds germinate. If the soil appears dry, gently water using lukewarm water and refill the reservoirs.
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After one fourth of the seeds germinate, usually seven to ten days, move the tray to a natural light location or under fluorescent lights for 16 hours per day.
Growing Tomatoes from Seed
Thinning
About a week after the seeds have germinated and the second set of leaves has formed, which are the first true tomato leaves, it's time to thin the tomato seedlings. By this time the seedlings are one to one and a half inches tall and the cells are becoming crowded. Examine each cell and carefully extract the stragglers, the weaklings, and the leggy ones. Leave the sturdiest, best-looking plants. It's no time for mercy--if you're ruthless about eliminating the weaklings you'll end up with stronger, healthier plants. One way to thin the plants is to use scissors and snip off the weaker ones at soil level. Another way is to pull the weaklings out. If you want to save some of the seedlings they should be transplanted to their own containers.
Sunlight
Once the tomato seeds have germinated, adequate light becomes essential. Ideally they need 12 hours of sunlight per day. Set them in a warm southern-facing window if you can. All things being equal, a humid bathroom works best. If a sunny window for the seed flats is not available, you can use artificial lighting.
Fluorescent Lights
If natural light is not an option, there are many types of grow lights available on the market; you can spend as little as ten dollars or hundreds. Simple 48-inch shop lights fitted with standard or high output cool white bulbs work very well for growing tomatoes from seed to the point where they're ready for transplanting to the garden. But if you're planning to grow tomatoes indoors to maturity you'll probably want to invest in quality full-spectrum grow lights. Fluorescent lights work best if suspended two or three inches above the tops of the plants; hang the lights by a chain on a hook so that the height can be adjusted easily. You don't have to spend a lot of money; I was able to build a cheap grow light stand for very little. The best lighting is directly under the center so it's a good idea to occasionally rotate the containers. Because the lights are cool there is no harm done if the leaves touch the bulbs.
Hardening
Brush the tops of the seedlings lightly using your hand each day. This helps harden the plant stems and causes them to grow stockier. This is called mechanical conditioning--it reduces leggy seedlings and results in more compact plants.
Fertilizing
If you've used a pre-fertilized soil mix, you shouldn't need to fertilize the seedlings, but if some of the leaves are yellowing, apply a liquid tomato fertilizer at half strength. If you haven't used a pre-fertilized mix, then a weekly application of fertilizer low in nitrogen but high in potash and phosphorous should give good results.
Transplanting Seedlings Indoors
After just a few days under the light, the young tomato plants will be four inches tall, have outgrown their cells and be ready to be transplanted to small pots. Some experienced gardeners believe their tomatoes thrive when transplanted to successively larger containers. It may be because of the fresh nutrients in the soil mix along with the added room for root growth. Follow these steps:
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Choose three- or four-inch plastic pots.
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Fill the pots with a soil mix similar to that used for seed germination or regular potting mix.
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Remove the seedling carefully from the seed flat. Cut out with a spoon or dull knife if necessary to keep the root ball intact. A small Rumford seedling tool may come in handy for lifting seedlings from flats. Rumford makes several small quality tools for handling plants in small containers.
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Plant the tomato seedling in its new pot, holding by its leaves or root ball, rather than its delicate stem.
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Press down on the soil gently around the rootball.
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Water well then allow the plant a couple hours to adjust before setting back in the sunlight or under the lights.
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Fertilize, water, and provide light as before until the plants are eight to twelve inches high and seven to eight weeks old.
Pruning Tomato Seedlings
If the plants appear to be getting too leggy, pinch back the tops. This will force the plants to grow stockier and sturdier, and also results in more blooms per plant.
Conditioning for the transition to outdoors...
When the average frost free date has arrived, and the soil temperature has reached 50 degrees F it's time to move your tomato plants outdoors. One week before, it's a good idea to "harden off" the young tomato plants by placing them in a protected spot like a cold frame. A wheelbarrow or toy wagon can also be used to move the young plants outside during the day and into the garage at night. This process will ideally firm up the plant tissues to withstand unpredictable and unfavorable weather conditions.
Now that you have made a great start on growing tomatoes from seed into healthy young plants, it's time for planting tomatoes into the garden or outdoor container!
