In this feature, garden authority Gayla Trail, the creator of YouGrowGirl.com, answers frequently-asked questions and offers gardening advice.
I don’t want to go to the expense of setting up lights; can I start seedlings on a windowsill?
Absolutely! To be fair, a grow light set up is ideal since you have greater control over growing conditions, most especially light. Since we can’t all afford the cash or the space to begin with, there is no reason why you should discount your windowsill as a seedling nursery until you are ready to step up your game. Fortunately, I have tricks that can help!
I know all too well from personal experience that not all windowsills are created equal. Many are wonky and uneven or too thin to hold pots, and some new-style windows don’t come with a sill, period! Worse still are the fluctuating temperature swings caused by baseboard heaters, drafts, and freezing glass. A windowsill can be the coldest place in your home or the hottest depending on a variety of factors. Unfortunately, spastic growing conditions can stress out sensitive young plants, leading to disease and death.
Fortunately, most seeds require heat, not sunlight to germinate. Start your seeds in a spot that stays consistently warm — on top of the fridge or a radiator are good options. Shift them to the sunniest windowsill you’ve got as soon as a bit of green is showing above the soil line. If your windowsill is drafty or cold, lay down a towel or old t-shirt like a blanket and then set your pots on top.
A south-facing window is your ideal. To be honest, anything else is going to get gnarly. I’ve had some success on less-than-ideal windowsills, but only with older seedlings that got a good start elsewhere. Plants grown underneath grow lights receive bright light from above as they would outdoors. Windowsills receive sun on an angle, causing plants to grow in the direction of the light. If the light is feeble the plants will grow lanky and weak as they stretch themselves in an attempt to get to it. The time of year will also affect your chances.
Tricks: Utilize east- or west-facing sills later in the spring when the day length and intensity of the sun has increased. Turn plants daily so that they receive equal light on all sides.
Some plants do better on windowsills than others. For example, tomatoes tend to be fairly forgiving and unlike most plants, lanky stems can be buried at transplant time. You’ll have the best luck overall with plants that will only be spending a few weeks at most indoors. Cucumbers and squashes are decent edible crop candidates as are cold hardy onions, kale, and broccoli since they can withstand temperature fluctuations. I’ve had good success with marigold, zinnias, and cosmos and a number of tough herbs including parsley, chives, summer savory, and chervil. There is no use bothering with radishes, beans, lettuce greens, peas, dill, and coriander. Save yourself the hassle and direct sow them outdoors!