The sooner indoor-started tomato seeds are up and growing, the sooner I’ll sink my teeth into a garden-ripe tomato, right?
Not necessarily. Earlier planting leads to better harvests only when seedlings have consistent, near-perfect conditions. And the earlier tomatoes are planted, the harder it is to give them what they need.
Slow and steady
The ideal tomato seedling (also called a “transplant” or “start”) plods along, growing steadily, making a seamless transition to the outdoors. Consistently moist soil and regular feeding are part of this prescription. Keep tabs on your watering by periodically poking your finger, use an electronic water meter down into the potting soil, or lift the container to check its weight.
There are a couple of ways to feed your seedlings. One is to add soluble fertilizer to the water; use a fertilizer formulated for this purpose and follow the instructions, because too much fertilizer can be as harmful as too little. Fish emulsion is a good, soluble organic fertilizer. Or you can mix into the potting soil some insoluble fertilizer that slowly, steadily releases nutrients. My potting mix includes one-quarter, by volume, compost, and this, along with a smidgen of soybean meal, steadily feeds my potted plants in sync with their needs. Cottonseed meal, alfalfa meal and feather meal are other organic, slow-release fertilizers.
Time to repot
To avoid any hesitation in the plants’ growth, they need to be shifted to larger pots as they grow. Repot whenever plants grow taller than one-half to two-thirds the height of their container.
The plants also need abundant light and relatively cool temperatures — ideally around 65 degrees. this is a combination not easy to provide on a windowsill or, without care, in a greenhouse. A sunny window in a cool room is ideal.
Artificial light is another option. Use a fluorescent light and keep adjusting its height so it’s within inches of the plant. Many seedlings can bask under a double fixture of two 4-foot-long fluorescent bulbs. (Incandescent bulbs aren’t the right spectrum).
Add a little stress
One more thing a tomato seedling needs for good growth is stress. It prepares the plants for buffeting wind, pelting rain, bright sunlight and cooler temperatures of outdoors. Brush your hands over the leaves or shake the plants one or two times a day and they’ll develop into stocky, dark green youngsters.
The time to transplant tomato seedlings outdoors is a week after the average date of the last killing frost — mid-May in Colorado, but you also know how variable it can be. The time needed to grow a reasonably sized seedling is about six weeks, so count back from that last frost date and hold back sowing seeds indoors until about then.
Then, harden the plants for a week by getting them gradually accustomed to the outdoors in a protected spot.
