To grow edible plants successfully you need around 12 hours of daylight (except for sprouts and microgreens). It does not have to be all sunshine, but it has to be a bright light. A plant will not die if it does not get the light needed, but it will not grow much either. Additional light for an indoor edible window garden may be needed.
Note, we are not experts in grow lights, we actually try to avoid them as much as we can. While experimenting with grow lights we recognized that there is nothing as good as the natural sunshine.
Growing an indoor edible window garden with natural light
Natural daylight is the best light for plants. It is hard to simulate real sunshine with electric light bulbs.
If you want to grow edible plants indoors without supplementary light, you will need a bright, sunny window. North of the equator the window for winter growing has to be facing south. During the winter months, we get no sunshine neither from the east nor from the west. As the season progresses, east-facing windows can be used and are better than the west-facing windows.
To use natural light for indoor growing we installed south-facing windows at the back of our garage. It allows us to use our many sun hours for indoor growing. We used recycled windows that will serve us many years without any additional monthly cost. Most winters we grow without growing light just taking into consideration the natural conditions.
Plant your plants in mid to late summer so that by the time the short winter days come, the plant has reached maturity. For example, Chinese kale produces new sprouts for months if we get them established before the days get too short for much growth.
What are those short days? If you live farther away from the equator, winter days will get very short. Those are below 10 hour days. From October 28 till February 14 the daylight in our area is less than 10 hours. Calculate your area’s “below 10 hour days” here.
Here is a picture comparison of some plants in the winter. In two months there was no growth worth talking about. These plants were in a cooler location (we talk about temperature in this post) at large south-facing windows with no additional light. The plants look healthy and as soon as the days will get longer and the temperature warmer, they will take off.
Greens are not as sensitive to light. The growth does slow down, but baby salad greens and even lettuce can still be grown, if the winter months are sunny, as’s the case in our climate.
The winter planting for the spring season is better done with additional grow light. For most summer seedlings we wait till the days are longer and start them then. We get better results that way. See our indoor planting schedule for the summer garden here.
Growing an indoor edible window garden with additional grow light
With a grow light you can grow an indoor garden in any corner of the house. There are many grow lights to choose from. Without a window, you would need a more expensive and advanced grow light we have no experience with those.
The beauty of a window garden is that you already have the best light available – real sunshine. You just need to supplement that light so you have more light hours.
We use 54W high output T5 fluorescent lights with a bulb life of 20,000 hours. Reflectors to improve light efficiency are helpful too. Of the fluorescent tubes that have been available in T8 and T12 models, this is by far the most efficient. The T5 grow light can produce 100 lumens per watt, which is almost unheard of in systems like this. This effectively means that it uses less energy to produce more light.
You want your grow light to be not more than 12 inches above the plants to make sure the plants can be flooded with as many photons as needed to grow, not just survive. With more powerful grow lights that radiate a lot more heat like HPS or HID the distance should be more than 12 inches. Remember that grow lights imitate the sun, but can’t really replace it.
Adding a grow light to a window can also benefit the whole room. In a kitchen window you might already have a light fixture above the window; just replace the regular fluorescence bulb with a grow light bulb.
Does it have to be a grow light? Yes and no. Grow lights are suited for plant growth because of the similar color temperature of bright daylight. However, if you want to use a simple fluorescent bulb you can, just make sure that the output of light is at least equivalent to 100 watts.
The warm red spectrum is recommended for flowering, and the cool blue spectrum is recommended for vegetative growth. But really, if you are going to burn energy, you might as well get a grow light. For you and the room, it will make no difference, for the plants it will make a huge difference.
The combination of a bright sunny window and additional light for an indoor edible garden is your best choice. The supplemental grow light plus the sun hours will make your indoor growth successful. You can even grow fruit like tomatoes, peppers, and cucumbers at a sunny window with an additional grow light.
How many hours do grow light have to be on
Depending on the plant you will want 12 -18 hours of light. As a rule of thumb leafy plants need less light, flowering and fruiting plants need more.
For example, turn the grow light on at 7 in the morning and let them on till the sun is up, after that in a window garden it can be turned off. In the evening do the same, turning the lights on as soon as the sun goes down, and leaving them on till 7 for a 12 hour day. Start earlier and leave on for longer for more hours as needed.
Also during cloudy days, you might want to leave lights on as well, especially if you are growing fruit-bearing plants. The more light, the better growth you will become. As you see in the picture above, the leaves under the grow light are bigger and healthier than those above. However, we kept the light low because of other plants in the same spot (not i. the picture). The cucumber plant is growing the Kratky hydroponic way.