Geranium Guide

Should You Be Growing Geranium Seeds on a Windowsill?

When it comes to growing geraniums indoors, it may be tempting growing geranium seeds on a windowsill, but this might not be the best choice. Sure, we know that geraniums like the sun and that many people have geraniums growing healthily on windowsills, but if you want to give your geranium seeds a good start, it’s best to avoid growing them on a windowsill. Let’s take a look as to why the windowsill is not a great choice and what alternatives are a better option.

The Problem with Windowsills

Ideally, geranium seeds grow best at soil temperatures between 70 and 75 degrees. When you place seeds by a windowsill, you are exposing them to uneven temperatures that can be harmful. For instance, consider the windowsills may be warm during the day when the sun is up by a south-facing window, but during the night, the area by the windowsill is likely to become one of the coldest places in the home. Seeds do poorly when they are exposed to these extreme temperature shifts as they thrive on consistently warm soil.

For instance, if the windowsill gets quite cool, this may cause disease and death to the seedling, while if it gets too hot, the growing medium/potting mix may become dry quickly, possibly causing the seedling to never germinate or germinate and then die. Also, consider the sun rays from a windowsill. When the sun light comes from the side, the seedlings will struggle and develop bent stems or they may get excessively leggy and thin.

Did you know? Soil temperature is different than room temperature. The temperature in your potting mix or other growing medium can be 5 degrees less than the indoor temperature of the room where the seedlings are growing.

A Better AlternativeHeat Mat for Geranium Seedlings

A better option for growing seedlings indoors is investing in a seedling heating mat offering bottom heat or artificial light sources such as fluorescent lights. With the help of a thermostat, you can ensure that your seedlings receive even, constant temperatures between 70 and 75 degrees. These even soil temperatures will help the roots grow well and the bottom heating mats provide help in preventing damping off which can take place when the temperatures are too cool. Also, the lights from the above, help the seedlings grow stronger, sturdier stems that are more straight and less leggy compared to seedlings receiving light from a windowsill.

“Seeds of most plants started indoors germinate sooner and produce healthier roots when the potting mix is warm, and bottom heat can help to prevent “damping off,” the death of tiny seedlings due to pathogens at the surface of the potting mix.”~University of Minnesota


University of Minnesota Extension, Starting Seeds Indoors.

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