Tips for growing tomatoes from seeds in Western Washington -- but not yet

·3 min read

The fourth of week of March is full of spring flowering bulbs, early blooming azaleas and rhododendrons, and more than a few lawn and garden weeds.

This is a good time to plant the seeds of cool season crops such as lettuce, radish, kale, cabbage and peas. In the flower garden, seeds of pansy, sweet pea and alyssum can go into the soil.

Q. I have started tomato plants from seeds this year. I just sprinkled the seed on top of some potting soil in a 1-gallon pot. I am thrilled that so many seeds have sprouted as we just have a windowsill for sunlight, not a greenhouse. My question is, now that the seedlings are about 2 inches tall, when do they go into their own pots and when do they go outdoors? — T.R., Sumner

A. Congrats on your seed starting adventure. Now you need to slow down.

Tomatoes are warm-season plants so they do not like to be placed outdoors until the end of May. This means you must provide the seedlings with maximum sunlight indoors for another few months to keep them from growing long stems and toppling over in search of light.

Separate the seedlings now by carefully picking out strong young plants to put into individual containers or small pots made of peat that you can easily transplant. Accept that many of your young tomato seedlings will be lost when you transplant the seedlings as their roots are most likely intertwined. This is why it is best to put just two or three seeds into a smaller, 4-inch container when you start tomatoes from seed.

Your next challenge is to give more light to the seedlings that survive the transplant. Garden centers and nurseries sell special lighting kits made for indoor plants. Unlike regular light bulbs, the grow lights have a full spectrum of light that the plants need. Sunlight from a bright window as well as grow lights is best.

The sad news for you is that tomatoes crave full sun and heat so planting the seed too early will actually slow them down as they sit indoors waiting for the weather to warm up. Next year try waiting until mid-April to plant tomato seeds indoors. Then they will only have six to eight weeks of weak indoor light before they can bask in the glory of real summer sun outdoors.

Tip: You can help tall and leggy tomato plants adjust by removing about half of the lowest leaves on the plant when it is time to move them into the garden bed. Wait until the soil is warm in mid June. Then dig a trench and lay the plant sideways into the trench so that you can cover most of the long stem with soil. The top half of the plant with foliage should be sticking up out of the ground. This allows the stem to grow roots out of the nodes that once had leaves growing from them. Planting your tomatoes sideways into a trench will give you a shorter, but better rooted tomato plant that ultimately bears more fruit.

Marianne Binetti has a degree in horticulture from Washington State University and is the author of several books. Reach her at