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Lighting Guide: Are Your Plants Getting Enough?

No matter what you're growing, make sure your plants have enough light. This guide will help you determine if your plants lack light and what you can do about it.

Giving your plants enough light is the single most important consideration for your indoor garden.

If you don't get this right, everything else is irrelevant.

Signs Your Plants Have A Light Problem

The appearance of your plants will tell you if they're getting enough light or not.

Too LITTLE Light

Look for . . .

  • Leaves. Pale green or yellow in color. May also curl or be thin and small.
  • Stem. Visible stretching or leaning towards the light source. Elongated.
  • Base. Many fallen leaves.
  • Growth. Slow growing or stunted.

Too MUCH Light

Look for . . .

  • Leaves. Faded and washed out. Dry, brown patches.
  • Stem. Plant may wilt mid-day when it's receiving the most light.
  • Base. Many fallen leaves.

Seedlings

For young seedlings, light is particularly important as the plants are so fragile.

With too little light, new sprouts will become stretched (leggy) and fall over. Seedlings should be moved to light immediately after they sprout.

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With too much light, the tops of the seedlings will become dry and brown. Either move the light away from the seedlings or the seedlings away from the light.

Indoor Lighting Considerations

There are four things you need to think about when lighting your indoor garden:

  • Type. Will you use sunlight, grow lights, or a combination of the two?
  • Duration. How many hours of light are there per day?
  • Intensity. How bright is the light?
  • Coverage. How far away is the light from your plants?

Each component is important to ensure your plants have enough light to thrive. I go through each one for both sunlight and grow lights below.

But in short...

When relying on sunlight, it's a good idea to experiment with different locations for your plants to find the best lighting conditions.

If you instead opt for grow lights (which I recommend using), then it may seem more confusing at first. However, your plants will grow faster, stronger, and more easily.

Sunlight

Most plants prefer placement near a clean, unobstructed, brightly lit south-facing window with at least 6-8 hours of sunlight per day.

Ensure outdoor temperatures are consistently above 55-60°F as a cold windowsill can prevent or slow growth. Avoid drastic temperature changes.

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Duration

With sunlight, the duration of light available is mostly the same every day. However, depending on the season and latitude the hours available every day will change.

More light is available in the spring and summer than in fall and winter. In the Northern Hemisphere, higher latitudes have less light per day than lower latitudes.

Intensity

While the intensity of light from the sun is constant, obstructions and the time of day affect how much light reaches your plant. The most intense light is directly in front of a clean, unobstructed South-facing window.

Dirty windows, other plants and trees, buildings, and any other number of things can affect the intensity of light that reaches your plants leaves.

Peak light intensity, depending on which direction your window is facing, is typically highest during the middle of the day.

The direction of your windows plays a critical role in how much light your plants receive. A south facing window is best (in the Northern Hemisphere), though an east or west facing window can work too.

  • South-facing: Provides the most light. Plants can be placed far from the window and still receive bright light.
  • East-facing: Much less light than south-facing. Plants can be placed a few feet from the window, but not much further.
  • West-facing: Same as east-facing, but transmits more heat. Use a sheer curtain during the middle of the day to prevent cooking your plants.
  • North-facing: Provides the least light. Plants must be placed directly in front of the window for any amount of light.

Coverage

While indoor plants typically don't have a problem with too much sunlight, if your plant is wilting, and you're keeping it watered, try moving it a few feet from the window or put up a sheer curtain during the middle of the day.

Grow Lights

Grow lights are specially designed light bulbs for growing plants. This means you can grow pretty much anywhere.

The most cost effective and energy efficient options are T5 fluorescent or LED grow lights.

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Duration

By using a timer, grow lights can be controlled to turn on and off at specific times. This is incredibly helpful, particularly if you plan on traveling for a few days, or even just overnight.

Grow lights should be left on for 16-18 hours per day for the fastest growth. 12 or more hours per day is ideal.

Don't leave them on 24 hours per day - give your plants a chance to rest.

Intensity

Most lights designated as "grow lights" will be bright enough to grow a plant. However, there are exceptions.

T5 fluorescent grow lights are an excellent, energy efficient, and cost effective option. While 1 bulb can work, 2 or more is ideal - particularly when that's the only source of light for your plant. T5 bulbs typically come in 2-4 ft lengths so plan your layout accordingly. Make sure to get a bulb rated at 6500°K (blue) for growing herbs or greens, and a 3000°K (red) bulb for growing flowering plants (tomatoes, peppers, etc).

LED grow lights are even more energy efficient than T5 lights. Some may give off a purple or pink glow. This is normal and part of their incredible efficiency - plants prefer certain wavelengths of light so the LED emits only what the plant needs. Make sure the LED light is at least 7-15 watts for adequate output and avoid very cheap options. Output from cheaper lights may not match the advertised wattage. For growing herbs or greens, get a blue or full spectrum LED system. For flowering plants (tomatoes, peppers, etc), get a red spectrum.

Coverage

Because the output of grow lights is less than that that of the sun (a good thing too!), the lights need to be kept close to the plant's leaves.

As the plants grow, simply adjust the grow lights up. Keep T5 and LED grow lights 2-12 inches away from the leaves, depending on the power (and heat output) of your light system.

If the leaves start to turn brown and crispy on the tips near the light, they may be getting burned, so move the lights further away.

Conclusion

That's it! You should now have a solid foundation for choosing the best lighting option for your garden.

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Questions or Comments?

David Stack

David Stack

A few years ago, I was a complete gardening novice... Since then, I have spent hundreds of hours researching, designing, and building indoor gardens. Now I'm sharing what I've learned with you.

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Lighting Guide: Are Your Plants Getting Enough?
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