Written by Dale Richardson - Updated: June 23, 2023
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A classic science experiment in school is to put a plant in a dark closet and see what happens. The outcome: it turns white, withers, and dies without the sun. However, there is a way how to grow vegetables indoors without sunlight. Read more to find out how.
To grow vegetables indoors without sunlight, the first step is to choose the right vegetables that will do best in these low-light conditions. Your plants will also need extra nutrients to grow in these artificial conditions. The last step, and perhaps the most important, is to choose the right light source and provide enough of it.
Plants need light, but sunlight isn't always available. Here are some practical tips to grow vegetables indoors when the sun isn't shining.
Vegetables, like all plants, need light to grow. They use the light to convert carbon dioxide and water into food through a process called photosynthesis . A plant's roots draw nutrient-laden water from the soil. When this water reaches the leaves, it is divided into oxygen and hydrogen ions by sunlight. The nutrients stay in the plant, the oxygen is released into the air, and the electrons from the hydrogen ions convert carbon dioxide into glucose which is the plant's main source of food.
Light is essential for healthy plant growth, but it doesn't have to be sunlight. Maybe your home doesn't have sufficient windows to let in enough sunlight for plant growth. Or maybe you live in a northern climate as I do, and the winter sun filtering through your south-facing windows is too pale to properly photosynthesize. Or maybe the perfect spot in your decor for your indoor garden is in the darkest part of your house. Whatever the reason, you can still grow your vegetables. Here are some tips to get your sunlight-free garden off to a good start.
The first step to growing vegetables without sunlight is to choose the right kind of vegetables for the artificial growing conditions you are providing. Some plants do better in low light than others, and your best bet is to choose shade-tolerant vegetables. Plants that produce fruit and flowers, such as tomatoes or peppers, generally need more light to complete fruit production than vegetables where you eat the plant itself, like lettuce or carrots. While fruit bearers can be grown under artificial light, they require more light on a different spectrum (more on this later).
Let there be light!
Most leafy green vegetables, such as lettuce, mustard greens, or arugula tolerate shade and only need a few hours per day. Beans, peas, and other legumes can grow well with 5 or so hours of sun, as will root vegetables. Cruciferous vegetables such as cabbage, cauliflower, or broccoli can be grown in partial shade as well, but these are trickier to grow and many gardeners have difficulty with their cultivation. And don't forget about mushrooms! Here is an article that details shade-tolerant vegetables that would do well under artificial lighting .
When your indoor plants have little to no sunlight, they will need extra nutrients to aid the photosynthesis process because artificial light is not as efficient as sunlight. When filling your pots for your indoor garden, it is best to use fresh soil if possible. Reusing the same soil over and over again will continually deplete the nutrients available in the pots and the plant's health with decrease. When filling your pots, mix plenty of compost or well-rotted manure into the soil so your plants have lots of food. We generally mix about 1/3 compost with 2/3 soil, but if your growing area is all but devoid of sunlight, you might want to make at least half the pot compost. If your plants have deep roots, you can put the compost on the bottom of the pot and the soil on top, but if the roots are shallow it is probably better to mix them.
As your plants grow, especially if they are continually bearing, like peas or tomatoes, you might need to fertilize the pots. If you do, choose a nice, organic fertilizer as it is more readily absorbed by the plant and is better for you and the environment.
Plants also need water, and it is important to monitor your plants to make sure they have an adequate supply. Potted plants dry out more quickly than when planted in the ground so it is important to keep the soil moist. Just as bad as under-watering, however, is over-watering. If the soil is too wet, the roots will not be able to breathe and the plant will quickly become diseased or rot and die.
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So, which light is best in the absence of sunlight? When choosing a light for indoor growing, it is important to consider the colour spectrum and output.
The colour of a light is determined by the light temperature which is measured in Kelvins. Red light, which stimulates flower production, has a low colour temperature between 2,000 and 4,000 Kelvins. Blue and white light, which is best to promote bushy plant growth, has a colour temperature of about 5,000 to 8,000 Kelvins. Direct sunlight is 4,800K, which is a nice mix of red and blue wavelengths to produce a healthy plant.
The output of light is measured in lumens . A lumen is how much light is emitted per second, and obviously the more lumens the better. Every plant will require a different amount of light for ideal growth, but a good rule of thumb is to try and provide between 300 to 800 lumens per square foot.
Lumens VS Watts
When growing vegetables under artificial lights, you want to provide an average of 14 to 16 hours of light each day. If your plants are in a room where there is no sunlight whatsoever, leave the lights on for 18 hours. While this can be done manually, a simple and cheap timer works wonders. You can tell if your plants are not getting enough light if they are leggy with scraggly white stems, and the leaves start to turn yellow.
There are a number of lights available on the market. Here are the different types generally used for growing plants to give you an idea of what works best for you.
LED grow lights are the most energy-efficient artificial light source available, and this is a very important factor since you are leaving the lights running for 14 hours a day. LEDs produce very little heat so you can put them right over the plants and they are very durable. They generally come in full-spectrum so they provide both red and blue light which is ideal for all plants. However, they are generally quite expensive, but here is a list of some that are under $100 . LEDs will also run for years.
Image by by Carmen Edenhofer
If you only have a few plants, you can use a simple lamp with an LED bulb . Choose a daylight bulb that will generally be around 5,000K which has a good colour spectrum. Many LED bulbs have an output of 800 lumens which will provide enough light for several pots.
Can I use a regular incandescent bulb?
Compact fluorescent lights are the most readily available lights you can get. They are inexpensive, fairly low heat, and quite small and compact. They are better suited for greens and seedlings and do not provide as good light for flowering plants. Their downsides are they are not very efficient, and they contain mercury which can be very dangerous when they are broken and not environmentally friendly.
Fluorescent tubes are easy to install and quite energy efficient. They are low heat and can be put right over the plants. They emit blue light so are best for starting seeds and greens.
As the name implies, HIDs put out a lot of light and are the lights typically used in commercial greenhouses. Unfortunately, they also produce a lot of heat and are not energy efficient, so they are not a great choice for the home grower.
Home-grown food should not be limited to those who have outdoor gardens. Everyone should have access to lush, green plants and fresh vegetables. This is especially true when we are stuck indoors on a dark winter's day, or in a small apartment with even smaller windows. While we might be deprived of sunlight, I hope these ideas help you give your plants the boost of light they need to thrive.
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