Starting Garden Plants Indoors

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Photo by Olha Pylpenko - Getty Images

Seedlings in planter

By March, most winter-weary Wisconsinites yearn for all things summer, including getting our hands dirty in the garden. Starting garden plants indoors is a therapeutic and economical way to feel connected with nature as we dream of summer days that lie ahead.

Starter plants, also known as seedlings, starts and transplants, are plants started from seed indoors and then transplanted to an outdoor garden once the threat of frost passes. A common myth is that elaborate greenhouses or expensive grow lights are needed to start seedlings indoors. Those tools are helpful, but any bright, sunny windowsill, especially those on south-facing windows, can serve as an area to grow seedlings.

Think about what plants you want to grow. Some plants do better than others when started indoors. Basic lettuce varieties, peas, beans, radishes, greens, broccoli, cauliflower and herbs do well. Tomatoes, peppers and eggplant can be also started from seed indoors, but they take a little longer.

Once you’ve got your seeds, gather some starter pots. Peat pots, cell trays and seed starting kits can be purchased, but repurposed household items like plastic clam shells from produce, egg cartons or yogurt cups, all rinsed out with drainage holes poked through the bottom, work well. You’ll also need seed starting mix or potting soil, a spray bottle of water and plant markers. The latter can be crafted from Popsicle sticks or handles from repurposed plastic cutlery.

Slightly Damp, Not Wet

Pre-moistening the soil can help with germination. Dump the soil into a large bucket and add just enough water to moisten it. Mix with your hands until the soil is slightly damp, but not wet. Fill the starter pots with the soil mix. Place a few seeds in each pot and press them into the surface of the soil. Some seeds won’t need to be topped with more soil, but larger seeds will need to be completely covered; consult the seed package for sowing directions.

Since there will likely be a few seedlings that won’t survive, plant a couple of extra seedlings per type of plant. Label each pot with plant markers. Place the pots on the drain trays on the windowsill. Mist the seeds with water and cover the containers with plastic cling film, the tops of plastic clam shells or other snug-fitting clear tops to create a greenhouse environment. A heating pad can be placed underneath the pots to generate more warmth. If you live in an older home with boiler heat, radiators, as long as they don’t get too hot, near sunny windows are a good place to put the pots or containers.

Keep the soil moist, but not too wet. When the seeds begin to sprout, usually within one to two weeks, remove the cling film or plastic domes. As the seedlings continue to grow, thin them out by carefully pulling the smaller ones from each pot so the strongest seedling remains. Over the coming weeks, keep the soil damp, but not wet. If the seedlings start to grow tall and lanky, they may flop over and wither. This can happen if there is too much or too little moisture, or too much or too little warmth, so try adjusting those elements.

More potting soil can be added to the base of the stems to strengthen the seedling as it grows. This is particularly helpful for tomato starts. Transfer starter plants into larger pots if they outgrow the original pots.

As that long-awaited planting day nears, the seedlings should be hardened off so they aren’t shocked by abruptly going indoors to outdoors. Move the starter plants outdoors into sunlight for a couple of hours each day and bring them back inside at night. Gradually increase the time the starts are left outdoors. After the last threat of frost passes, the plants are ready to be planted into their outdoor summer garden.