Most plants need light to thrive because light is essential for photosynthesis. Without it, plants could not make food. But light can also be too intense, too hot, or last too long for growing healthy plants. In general, more light seems to be better. Plant growth accelerates with abundant light because more of the plant’s leaves have exposure; which means more photosynthesis. Two years ago I left two identical planters in the greenhouse for the winter. One was placed under a grow light and one was not. By spring, the difference was astounding. The plants in the container under the light were nearly 30% larger than those not receiving the additional light. Other than for those few months, the two containers have always been side by side. Years later it’s still evident which container was under the light. The container that did not get the added light is perfectly healthy, just smaller. With many plants, however, winter days are just not long enough. Many plants need 12 hours or more of light per day, some need as many as 18.
Adding grow lights to your greenhouse is an excellent option if you live in the North and don’t get many hours of winter daylight. Grow lights are an excellent option to replace some of the missing rays. Maybe you do not have an ideal southern location on your property for a greenhouse. Use grow lights to supplement the day’s length as well as the quality and intensity of light. If your greenhouse covering does not diffuse sunlight well, you can add lights to fill in shadows for more even growth.