Idaho Falls Community Garden Association

Tomatoes from Seed
"Only two things that money can't buy / That's true love and homegrown tomatoes."

Warmed by the sun, sweet and juicy, the incomparable taste of a homegrown tomato is a lure that most gardeners can’t resist. So in our challenging climate, the successful culture of Lycopersicon esculentum, as the tomato is known in more exalted circles, is the Holy Grail for many gardeners. Growing from seed opens up a world of almost unlimited possibilities and makes the pursuit of the perfect Idaho tomato a real adventure. Following are some guidelines to help you in your quest.


Good seeds are the prerequisite for good plants. No matter how good your fertility, soil, water and light conditions, if the genetic material of the seed is inferior or damaged the end product will be significantly affected. It pays to use good seed! Whether your seeds are ‘store-bought’ or ones you saved yourself, you can optimize their viability by providing good storage conditions: the cooler and drier, the better.

We say soil, but what we really mean is a sterile soilless mix usually having some combination of peat, vermiculite, perlite, coconut fibers and/or sand.  The mix should be light, airy and able to absorb water easily. Do not use soil from outside. Its texture and weight are not optimal for seed starting and, more importantly, the danger of disease is much greater. Most garden centers carry good quality, reliable brands. If you know an experienced gardener or want to search the internet you can also find many recipes for making your own mix.

While good light is not necessary for germination, it is important for growing a sturdy, healthy seedling. The most effective method I have found is to use standard shop light fixtures with regular florescent  bulbs. 2 lights suspended side-by-side will give you enough space to grow 3  17"x17” flats, approximately 192 plants in deep 6-cell packs. Full spectrum bulbs that mimic sunlight are available but regular bulbs do a good job and are much less expensive. Suspend the lights just an inch or two above the plants in the flats. (Using the chain links that come with the lights makes adjustments easy.) The plants should have 16-18 hours of light a day. Placing your seedlings in a sunny windowsill DOES NOT provide adequate light and will produce spindly, weak seedlings.

Not too little but not too much  … this is the vague distinction you will gradually become adept at recognizing as you get more experience.  Either too much water or too little can stress plants and make them more vulnerable to other problems.  When your seeds are initially planted it is very important to keep the soil uniformly moist. You can do this by covering it with plastic wrap of some kind (slipping your planting container inside a plastic bag and closing it loosely is easy and effective) or planting in a flat that has a clear plastic lid . The plastic maintains the humidity at a constant level. Often you won’t need to water until after the seeds have sprouted and the plastic is removed. Once plants are growing bottom watering - setting the containers in water and allowing them to soak up what they need - is the preferred method since it ensures thorough watering and avoids wetting the leaves. Water the plants when there isn’t obvious moisture in the first inch of soil or about once or twice a week depending on the size of the plants. If the leaves show signs of wilting water the plants right away.

The optimal temperature for germination for most plants is 70 - 75°F. A source of bottom heat will provide more uniform soil temperature and faster germination. Propagation mats are widely available for this purpose but if you take proper care to avoid getting the blanket wet you can also use an old electric blanket. (In addition to protecting the blanket from moisture be sure that you don't fold the blanket over on itself.) Once the seeds have germinated and been moved under the lights there is no further need for bottom heat. In fact, a sturdier, more compact plant will result if you can grow the tomatoes on in a cooler environment of about 60-65°F.

Just about anything that can hold soil and provide drainage will work. All garden centers have products for this purpose and many adequate containers can be adlibbed from things you have at home. There is even a tool available to form old newspapers into bio-degradable individual paper pots. If you are re-using containers be sure to sterilize them in a 9/1 water to bleach solution first.

There is no need for any additional fertilizer when germinating the seeds. Once the true leaves begin to appear you can fertilize with fish emulsion or other good organic fertilizer at a ¼ rate for the first few weeks gradually increasing to ½ rate. Check your starting mix to determine if there is already some fertilizer in the soil. If so, adjust your additions downward. Don’t fertilize within 3 days of transplanting as it can cause root burn.

Growing Up
If only it were so easy with our kids! All that’s necessary for our tomatoes is to provide conditions that allow the plant to be in a continuous state of growth. Research shows that the restricted root development caused by growing plants in containers that are too small results in stunted plant growth.  To avoid this problem do not leave seedlings crowded together and transplant the seedlings to larger volume pots when they begin to outgrow their container. First transplanting should be done when the first true leaves appear. If plants are started 6-8 weeks prior to the last frost they would typically be planted up to a 4" pot by the time they are ready for transplanting.

Hardening Off
This can be a make or break exercise. If you’ve spent 8 weeks growing lush and vigorous plants and then take them directly out and plant them in the garden  you could well loose the advantage of all your careful preparations. All it takes to successfully harden off your plants is gradually increased exposure to the elements. Start by taking the plants outside for an hour on a calm, sunny day. Double the time spent outside each day and after the 4th day the plants can be set into the garden. If conditions are windy or cloudy adjust the exposure time accordingly. Be sure to keep them well watered.


Materials :          containers      sterile potting mix        seeds        plastic bags        plant markers

Fill your containers with starting mix. Water lightly if mix is dry. Make indentations in soil mix about 1/3” deep - 2 per cell in a 6-cell planter.  Place a seed in each indentation, lightly cover and press. Water GENTLY and insert marker with variety name and planting date. Cover with plastic and place in warm place. (Light is not required for tomato germination.) Move under lights as soon as your seeds have emerged, usually 3-10 days. Once true leaves have emerged thin or transplant the seedlings so that each container has only one plant. When you are moving the seedlings be sure to handle them by the leaf and not the stem - damaged leaves will be replaced, damaged stems won’t! Continue to water as directed above and remember to keep the light source no more than a scant two inches above the plants. Begin the organic fertilizer several days after transplanting and continue to transplant to larger containers as necessary.  When the time comes to transplant outside remember to allow a few days for the hardening off process. You’ll be glad you did.


Here are some places to go to learn more about growing great tomatoes.
· National Gardening Association   - Search for tomatoes and you’ll get 200+ articles on all aspects of tomato growing, 1900+ FAQs and over 100 tips.
· Cornell University Home Extension information site
· I.F. Community Garden Association Green Links -  Good links to several informative gardening sites as well as information about late blight.
· Any good gardening book: New Seed Starter’s Handbook, Your Organic Garden, The Victory Garden, etc.

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