Growing Tomato Plants from Seed

by Ken Lain, the mountain gardener

I long have had garden success by putting started tomato plants in my garden rather than sowing seed directly into the soil.  This technic also guarantees I’ll be picking fresh juicy vegetables 2-6 weeks earlier than my gardening friend who chooses to start tomato seeds outside.

tomato-varietiesSo why start tomato plants from seed? Since tomatoes are heat lovers, most gardeners don’t have growing seasons long enough to start tomatoes from seed outdoors. Consequently, tomatoes usually are started indoors by seed.

Tomato Trivia – There are more than 3,000 varieties of heirloom, aka heritage, tomatoes in active cultivation worldwide, with more than 15,000 known varieties.  Beginning in April we at Watters will have over 83 varieties of heirloom/heritage tomatoes in stock.

As a garden center owner, grower, and home gardener, one of my favorite winter activities is choosing which tomato varieties to grow each year.  The old standards and proven favorites are ‘no brainers’, but I also like to introduce new varieties that have promise, nostalgia, or just look like fun to grow.  So in some respects, my customers are guided by my whimsey.   It’s part of the fun of gardening.  I have my tried-and-true varieties (I’ll share their names as we get closer to our summer plant dates) but with so many types to choose from, sed is the only way to expand your choices beyond the starters the garden center will offer this spring.

Growing healthy tomato plants ~

Organic Seed – Look for certified organic seed.  I would go so far as to choose only certified non-GMO seed, or non-Genetically Modified Seed.

Disease Resistance –  Verticillium Wilt is a common problem in mountain gardens.  If you know your area is prone to a particular disease, look for varieties with built-in resistance to specific diseases.

Plant Size – The better seed packages give the mature size of the plant. In general, determinate tomato plants tend to be smaller than indeterminate tomatoes. Small plants for containers often have names like ‘patio’ or ‘pixie.’

Harvest Time – If you want your tomatoes all at once, for preserves and canning, look at determinate varieties.  Indeterminate varieties bear a few fruits each day over a longer period.

Tomato seed germinates within 5-10 days. The plants develop fast, so seeds should be started 6-8 weeks before they are to be planted outside. The transplant date will depend on the last frost date of the area where the starts will be planted.  In the Prescott region, our last frost is historically May 8th.  That means most seedlings are being started in early March.

Preparing the Containers – You can plant in a variety of pots.  Just make sure your container is at least 3 inches deep with good drainage, that is, a seep hole in the bottom of the pot. Here at Watters Garden Center we have very inexpensive peat pots that are especially for tomatoes.

Pre-Dampen the Potting Soil – It’s more efficient to dampen your potting soil before putting it in the pots. Pour in some water and work it throughout the medium. Keep adding water until the mix stays compressed in your hand but is not dripping wet. It should break apart when you poke it with your finger.

Fill the Pots – Fill your containers and gently firm the soil so that it is about an inch from the top of the pot.

 Plant your Seed – Make a 1/4 inch long furrow in the planting mix in each pot. Sprinkle 2–3 seeds into the furrow and cover them with a bit of potting mix. Gently firm down the mix so your seeds make good contact with the soil. Spray the surface with water if it doesn’t feel moist enough.

 Be Patient – At this point, you should place your containers somewhere warm.  Check them daily to make sure the soil is moist but never soggy.  I like to put my containers inside plastic bags or cover them with plastic wrap, making a mini greenhouse. Remove this plastic covering as the seedlings emerge.

Tomato Care – Once your tomatoes have true leaves it’s time to start feeding them. Any good liquid fertilizer can be used once a week. Dilute it to half the label-recommended dose.  I use liquid fish fertilizer until my plants are put out in the garden.

Light is critical – Keep your tomato seedlings close to grow lights and rotate the plants if they seem to be growing or leaning to one direction.  Any daylight bulb or full spectrum light will work.  This time of year a window sill (without supplemental lighting) will lack sufficient light and will give your seedlings the chills.

Sturdy Stems –  In a garden, nature’s winds make for sturdy tomato plant stems.  Simulate this effect indoors by putting a fan on your plants for an hour a day; put the fan on a timer and carefully monitor each plant’s water needs.  In lieu of a fan, you can run your hand across them each time you walk past hem.

More Room Needed – When your tomato seedlings are 2-3 inches tall and have several sets of true leaves, it’s time to give them more space.   Three- to four-inch containers are good for seedlings of this size. You may need to move them to larger pots later if the weather is threatening frost come time to plant them outdoors.  If more than one seed germinated in your containers, you must thin them. Either gently jiggle entangled roots apart or snip off the weakest seedlings at soil level. Plant the tomato seedling a little deeper than it was in its original container. If tall and leggy, you can plant it right up to its topmost leaves. Firm the soil gently around the seedling.  Your seedlings should be at least 4 inches tall at transplant time.

Transplanting depends on our last frost date, that May 8th mentioned above, but err on the side of caution. If you put the plants out too early, they could be killed by a late frost or set back by too cool weather. Tomatoes planted a little later in the season will quickly catch up to earlier transplants stunted by the cold. In general, when night time temperatures remain above 45 degrees it is safe to transplant tomatoes into the garden.

Planting Seedlings Outdoors – Seedlings should be planted more deeply in the garden than they are in their pots.  This will encourage new roots to form all along the buried stem. They may be planted all the way up to the top couple of sets of leaves, if possible. This is especially good for plants that have gotten too tall indoors, and you want them to become stockier and stronger.  If you can’t dig deep enough, you can always plant them lying sideways in a furrow. The top of the plant will find the sun and grow upright in a few days.

Continued Care – Stake plants ASAP after transplanting to prevent root disturbance.  Give them a good drench of water and be patient; they should start flowering as the days warm into the 80’s. Tomatoes can be prone to diseases of both the leaves and fruits.  The best defense is to keep your plants healthy and vigorous. Give them regular water, leave room between plants for good air circulation, and check them daily to catch problems early.  If in doubt, bring your questions to one of Watters’ plant ambassadors here at the garden center.

What You Will Need ~

Tomato Seedsverify that your selected seed is organic and non-GMO.  A word of caution: it’s easy to get carried away buying too many tomato seeds. A family of four can easily feast throughout the summer on 6 plants.

Containers – Any small pot or container, at least 3 inches deep, will suffice, as long as it has drainage holes at the bottom. Take-out containers, yogurt cups, and juice cartons are all viable options.

Watters Potting Soil – This planting medium is blended to absorb water while letting the excess drain. Soil from the garden is never recommended for seedlings.  We also have Seedling Potting Soil specific to this project.

Labels – You can write varieties’ names on the sides of the containers or use popsicle sticks or plastic knives. Inexpensive plant labels are available here at Watters.

Water – Keep your seedlings moist but never soggy.  Never use water from a water softener; the salt damages seedlings.

Light – You won’t have to worry about light until the seeds germinate.  Any daylight bulb or full spectrum light will work.

Until next week, I’ll see you at the garden center.

Ken Lain can be found throughout the week at Watters Garden Center, 1815 W. Iron Springs Rd in Prescott, or contacted through his web site at or .