Starting Tomato Seeds


 Missoula experiences roughly 19 frost free weeks each year (approximately 133 days). According to the National Climate Data Center the average first frost free date is May 19th and the average last frost free date is September 27th. For tomatoes to grow and produce fruit they require more than a frost free day; they need ambient night temperatures of 55 degrees or higher. 55 degrees or warmer? That means some years the perfect tomato growing season for Missoula gardeners is limited to July and August, 60 short days! One way to extend this short tomato season is to either purchase sets (plants that are already partially grown) or start tomato seeds indoors.

Buying sets is a great option if you don’t have room for a few trays of seeds or if you realize on May 25th that you want home-grown fresh tomatoes for summer salads. One of the benefits of starting your own seeds is getting to choose from the very wide selection of tomato seeds available. Variety names are as unique as the flavors embodied in the fruit: Chadwick Cherry, Pierce’s Pride, Black Icicle, Chocolate Strips, Violet Jasper, Mortgage Lifter, Ozark Pink, Belize Pink Heart, and Moonglow to mention just a few. Here are my favorite varieties: Oregon Spring, Yellow Pear and Prairie Fire from Fisher’s Seeds in Belgrade, Montana; Cour di Bue and Cosmonaut Volkov from Baker Creek Heirloom Seeds in Mansfield, Missouri; Ranger and San Marzano from Territorial Seed Company in Cottage Grove, Oregon. A quick note about the Oregon Spring Tomato: developed at Oregon State University, it is one of the few tomato varieties that will set fruit in cool temperatures and is a great option for an early Missoula crop. The down side to starting seeds indoors is that it requires investing in some equipment and serious attention if you want to grow strong plants.  Plants grown in a window tend to be pretty spindly because they have to lean toward the light.

When choosing sets or seeds, it’s wise to ascertain if the tomato is determinate or indeterminate. Determinate tomatoes bear a full crop at one time and top off (stop growing) at a specific height. They are great for containers or smaller spaces and are often the best choice if you want to can your tomatoes as most of the fruit will ripen at the same time. Indeterminate tomatoes produce vines that continue to grow and produce fruit until killed by frost. They provide fruit throughout the growing season but can be “unruly” in the garden when it comes to space.

Six to eight weeks before you want to plant outside (approximately June 1st in Missoula) you’ll want to start your seeds. In addition to tomato seeds, you’ll need sterile seed-starting mix, containers, and labeling sticks. You can purchase seed-starting mix at a garden store or nursery or make your own with peat moss, vermiculite, and perlite. Thoroughly combine the starting mix with warm water before you begin. Any container will work for the initial planting. You can use an open tray or swallow box lined with plastic and a few holes poked in the bottom. You can buy seed starting kits with single or multiple cells and clear plastic covers. You can also buy peat or manure mini-pots to start your seeds in.

Once your containers are filled with starting mix, make shallow holes or furrows ¼ inch deep (remember the rule of thumb when planting seeds: plant a seed at a depth roughly twice its diameter – in the case of tomatoes, that’s about 1/4 inch). If you’re depth challenged, measure and mark a chop stick to ¼ inch deep and use that. Sow one or two seeds in the bottom of the hole for individual containers or cells or ½ inch apart in furrows if using trays or boxes. Gently pinch soil together to cover the seeds. Water carefully and label each variety. If you bought a commercial seed starting kit with a cover, put the cover over the flat. For other containers, place the containers into a loose-fitting plastic bag – leave the end open for circulation. This keeps the mix moist; seeds won’t germinate if they dry out. Put your containers in a warm place: 75 degrees to 80 degrees Fahrenheit.

As soon as the seeds begins germinating and stems show above the soil (around day 7 or so), it’s important to provide a strong light source such as grow lights or white florescent lights. Seedlings need 14 to 16 hours of light per day to grow properly. If using a grow lamp, set the lights just a few inches above the seeds. This will help ensure sturdy plants rather than spindly, yellowish, light-starved seedlings. Putting them in a window tends to grow leggy, light-starved seedlings as well.

After about 30 days, the first “true” tomato leaves begin to appear above the baby cotyledon leaves (those slightly thickened leaves that were first to show after the seed germinated). At this stage, if you used trays or put multiple seeds in mini-pots or cells, it’s time to transplant the seedlings into larger, individual containers (at least 3-4 inches in diameter) so they have room to grow and develop.

Carefully, and gently, lift seedlings from below using an old fork or small spoon. Hold gently to the baby cotyledon leaves and try to scoop up the entire soil ball from below so you get all the roots. If roots have grown together, tease the seedlings apart. Transplant each seedling into its own container filled with good quality potting soil. Each seedling should be inserted into a hole in the soil so that the soil comes to the base of its baby cotyledon leaves. Tomato seedlings will grow new roots along their buried stems, resulting in a sturdy, vigorous plant.

When the Missoula’s nights finally stay 55 degrees or warmer, it’s time to plant your tomatoes outside. (You can plant outside before warm nights arrive by using season extenders such as cold frames, wall-o-water or frost cloth around/over your plants.) Before you plant outside, “harden off” your plants by moving them outside into the sun for a few hours a day over a week’s time. Once hardened off, if the plants are more than 6 inches tall, trim off the bottom branches before planting and settle the seedling in a hole so the entire stem is covered up to where the leafy branches begin. Gently pull soil around the plant, firm and water. Even if you’ve hardened off your plants, I recommend you transplant on a cloudy, slightly cool day. Depending on the variety you’ve chosen to plant, you’ll have ripe, delicious tomatoes in July and August (and if we’re lucky, September too)!