When life gives you lemon trees, know their light requirements! Understanding lighting for indoor dwarf citrus

For dwarf citrus lovers in the Northern Hemisphere (or the northern part of the United States), your plants have likely spent the summer outdoors luxuriating in the sunshine. But as fall settles in, the weather cools down, and you start to bring your trees indoors, you’ll need to provide the right indoor environment for them to flourish. This means understanding the type and amount of light they need and setting up a lighting system that fulfills their unique needs.

You probably know that sun-saturated climates and citrus trees go together. There’s a reason that, in the U.S., citrus growing is limited to places like Florida and California: citrus loves the sun, and grows in fruity abundance in places where it has a long, warm growing season.

In other words, citrus needs light, and plenty of it, no matter where it’s grown.

Why do plants need light?

Plants make their own food in a process known as photosynthesis. In this process, plants use the energy captured from sunlight in order to produce tissue. Chlorophyll – the green pigment found in leaves – is the basis for photosynthesis, and enables plants to use this stored energy to convert CO2 into glucose. Through photosynthesis, the plant produces oxygen which is released into the air. This process is taking place all the time, all over the planet, and the oxygen that results is the basis for every breath you take.

As far as your indoor citrus setup goes, this makes it easier to understand why it’s so important to provide light for your trees.

But not just any kind of light will do. You need to find the right balance of natural sunlight and grow lamps to help your trees do what they do best.

The right kind of light for citrus growth – or, “yes, I have no lemons”

While some houseplants do well with low light levels (or no light at all), this is not the case with citrus.

Different types of citrus need different types and levels of light depending on their native habitat.

To know what kind of light you have, let’s consider some definitions.

Bright direct sunlight or the illumination from a grow light travels directly from the light source to a plant. This kind of light casts shadows. Bright direct sunlight is best found near a south- or west-facing window. Bright direct light is best for lemons, limes, and oranges, which grow in open groves that offer full sun.

Filtered light – similar to bright indirect light – is filtered through a material such as a sheer curtain or a forest canopy. Similar to bright indirect light, it does not cast shadows and can be found near windows that face east or north. Australian Finger Limes can handle filtered indirect light that mimics the dense understory of the Australian bush.

At the same time, plants need a period of darkness in order to produce healthy growth (especially flowers and fruit), and rely on changes in the day length to help them “know” when to produce flowers. Too much light can result in stunted growth and disrupt the flowering stage, which in turn interferes with fruit production.

In other words, too much light = no flowers = no fruit.

Is the light from a window enough?

If you live in the northern hemisphere, the answer is no – especially during the winter.

Citrus trees need 6 - 12 hours of bright, direct light each day in order to produce fruit. Either the sun or a grow light are satisfactory sources of light for this purpose. With any less than that, the plant will survive, but the chances of fruit production drop off to zero. If you are interested in indoor citrus for their ornamental appeal but don’t care about fruit, five or six hours of light daily will suit your tree’s needs just fine. In the northern US – or in any place where the temperature drops below 50 degrees Farenheit in the winter – a grow light will be required to satisfy citrus’s light requirements for fruit production.

Choosing and using a grow light

Installing grow lights during the winter to supplement natural light sources will ensure that your citrus tree will receive the correct amount of light for its needs.

It’s important to select the right kind of light. A bulb that you use for germinating tomato seeds or growing herbs won’t do the trick. You want to simulate the light conditions of sun-drenched groves, and the best way to do this is with a full-spectrum bulb. You can simply get a full-size plant bulb to use in a regular fixture, or go all out with the many and varied setups available on the horticulture-focused market.

There is an enormous range of features to browse on said market. You can choose from gooseneck lamps, free-standing tripods, and ceiling-mounted fixtures. There are full spectrum lights and lights containing only reds and blues. You’ll find built-in timers to allow for easy control of the on and off times, an ultra-flexible lamp head that can be adjusted both horizontally and vertically for different indoor plant growing needs, and – for the tech nerds out there – even one with a control panel board and remote control that allows you to adjust the light’s brightness levels, runtime, and lighting modes.

Your head will probably be spinning from all the choices. Mine certainly was when I started my own indoor growing journey. Allow me to spare you some of the frustration, help you keep it simple (and save money) with these recommendations for choosing a grow light.

• Look for a full-spectrum LED light. These mimic natural sunlight and are preferred by many growers. LED lights stay cool, use very little energy, and are long-lasting (up to 10 years in many cases depending on the quality of the fixture). LEDs are more efficient than incandescent bulbs (which you shouldn’t be using on your plants anyway) and can be customized to provide the amount of light you want.
• Stay away from incandescent bulbs (ordinary household utility bulbs – which are becoming harder to find). They don’t produce the kind of light needed for plant growth.
• Ditto for metal halide lights, which run much warmer than LEDs, have a much shorter life, are more costly to run and replace, and also pose safety hazards from potential burns on account of their high running temperature.
• Keep the light on for 6 - 12 hours per day. Remember that plants need periods of darkness in order to grow properly, so steer away from the temptation to make them grow faster by keeping them lit for 24 hours at a stretch. It won’t work and you’ll end up with stressed plants.
• Use a timer. This will ensure that you won’t need to remember to turn the light off and on, and the tree receives the correct amount of light if you forget to turn it off and on, or if you’ll be away at those times.
• LED lights should be kept at a distance of between 2 inches and 3 feet from the trees. That is a wide range, but the ideal distance depends on several factors including the heat output of the bulb, the size of the tree, and whether the tree is in its vegetative or flowering stage. Since grow lights emit heat as well as light, monitor the temperature of the area around the tree. If it gets too hot, move the light farther away or change to a bulb that emits less heat. As the tree grows, move the position of the light so it remains at a constant distance from the foliage.
• If you have a large tree, an overhead light provides the best coverage. If you don’t use an overhead light, rotate the pot periodically to ensure that the whole tree gets the maximum amount of light.

Ready to grow?

Indoor citrus growing success is a matter of providing the right kind and amount of light, among other factors. Whether that means a fancy growlight setup or a simple full spectrum bulb, you can have thriving citrus trees living in your home. It’s a spectacular reward for a little time spent learning about the needs of these beautiful plants. Happy growing!

Wait! I have questions!

Email me at eastnashgreens@gmail.com and I may answer them in a future post.

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