Everything you always wanted you know about indoor dwarf citrus tree care (but were afraid to ask)

So you’re the proud owner of a dwarf citrus tree. Congratulations! Your miniature tree should give you many years of enjoyment while enhancing your indoor decor.

Many dwarf citrus varieties -- including Mandarin Orange, Key Lime, Australian Finger Lime, Persian Sweet Lime, Calamondin Orange (aka Filipino Lime), and Makrut Lime -- can also produce fruit when grown indoors.

While these plants are not difficult to grow, they are particular about their care. Since they grow fairly slowly, you have plenty of time to read up about their needs. This is a great place to start! Here I provide the basics of what you need to know about raising healthy, happy dwarf citrus trees.

Soil

You can’t get more basic than soil.

Citrus requires acidic soil. Any soil with a pH below 5 is acidic but the ideal range for citrus is between 5.8 - 6.5. You can use pH test strips to determine your soil pH.

Since this is a site devoted to organic gardening methods (for reasons I’ll make clear in another post), I am only discussing organic soil options. Citrus does well with soils formulated for cactus and succulents, like Espoma Cactus Potting Mix. If you’re a DIY-er, 511 mix is an economical option for making your own bulk citrus soil blend You can find instructions for making 511 mix in the Files section of the Indoor Citrus Tree Growers Facebook group. There are also a number of videos on Youtube.

Light

If you want your tree to produce fruit, adequate light (whether as sunlight or the rays from grow lights) Citrus loves sunshine. It originated in sun-saturated parts of the world, after all. At least 6 hours daily is essential.

If you move your trees outdoors during the warm weather, too much sun (especially the harsh glare of late afternoon sun) can burn the leaves especially when the plants are young). Provide filtered light or partial shade during the hottest times of the day while your tree is still small. Even mature trees like some afternoon shade.

If you're growing indoors under grow lights, 8 to 12 hours of on time is ideal.

Potting and transplanting

Use a pot no larger than necessary so that the soil can dry out between waterings. Your seedling should be in a pot that's no more than 4 inches wide by the time it's about 5 inches tall.

You’ll know your dwarf citrus is ready for transplanting when the roots start to show above the soil or start to emerge through the bottom hole of the pot. Move the plant about once a year to a slightly bigger size pot until you reach a 18-24 inch diameter pot, where your tree will grow happily for years. The pots must have drainage holes, which should be covered with a small stone, a piece of broken pot or a piece of screening, so that the soil doesn’t wash out. The pot can be plastic or clay, but remember that while clay pots need more frequent watering, plastic pots can hold too much water, especially in colder weather.

Water and Humidity

The most important rule here is not to overwater. In general, citrus trees like periods of comparative drought followed by a thorough soaking, a process that mimics their native growing conditions. To determine if it’s time to water, insert a finger or a sharpened wooden dowel stick into the soil to see if it’s dry further down near the roots. Don’t water just because the soil looks dry.

All of that having been said, there is variation among varieties in terms of how much water they like. Makrut lime, for instance, likes a consistent evenly damp soil surface, similar to a wrung-out sponge.

Citrus leaves enjoy high humidity levels. They will drop leaves in the winter if humidity gets too low. Provide a nice humid atmosphere that mimics a rain forest by misting the leaves, using a humidifier, or by keeping a bowl of water next to the tree. Another option is to put the tree in a humidity tent.

Temperature

Citrus trees – being subtropical plants – can be kept outdoors during warm months. They do, however, need to be brought indoors when temperatures dip below freezing. Indoor temperatures of 60 degrees and above are ideal. Keep your tree in a spot with good air circulation, but avoid drafts from heating and cooling vents.

Fertilizing

Citrus seedlings do not require feeding in their first half year of growth as long as they are potted in a high-quality potting soil. They are deriving nutrients from the soil and do not need additional fertilizing.

Once the roots develop and begin to take up more space in the pot (approximately a 1:1 ratio of roots to soil, though there is no hard and fast rule), you can begin to fertilize using a dilute fertilizer as described below.

Citrus trees need high amounts of nitrogen. Feed your potted citrus plants regularly with a fertilizer that contains nitrogen, phosphorus and potassium. Check the package label for micronutrients and micronutrients, including iron, magnesium, manganese and zinc, which are important for plant health. Citrus fertilizers (such as Citrus-tone by Espoma or Happy Frog Citrus and Avocado Fertilizer) are an easy option as they contain a balanced blend of nutrients.

Apply fertilizer as new growth starts in late winter to early spring, and repeat every 2 - 3 weeks. Fertilize about every 3 - 4 weeks during the prime summer growing season. During the winter, once every six weeks is sufficient.

Yellowing leaves are a sign that plants need feeding. A quick way to address this problem is to use a dilute solution of kelp or fish emulsion fertilizer. Check the package instructions for ratio of fertilizer to water, and use double the amount of water the first time you feed it to the plant. Let the plant dry down, then feed again. Gradually increase the solution strength each time you water. After a few feedings over several weeks' time, the yellow color should fade.

Pests

If you’re growing citrus in pots outdoors in moderate climate zones, your citrus is unlikely to experience significant pest pressure. It may get leaf miners, but these don’t do enough damage to warrant intervention.

However, citrus trees grown indoors are likely to be affected by pests because of the absence of predatory insects like ladybugs, predatory wasps, and lacewings. The lower humidity levels common with indoor growing also contributes to pest problems.

To protect your plant against common indoor pests (including scale, mealybugs, aphids, and spider mites), prevention is usually the best course of action. Spraying your tree with a mix of water, dish soap, and vegetable oil can go a long way toward removing the bulk of unwanted inhabitants. Adding some neem powder to the soil can also keep pests at a minimum.

Gnats (which you will have more than likely) are more of an annoyance than a problem.

Pruning

Unless you're planning to cut a hole in your ceiling to accommodate your growing tree, there's no escaping the topic of pruning. And yes, even though these are dwarf trees, they will need pruning to maintain their health and shape and prevent them from attaining unwieldy sizes in your growing space.

Here are some general guidelines.

1. Begin pruning when the tree is small rather than wait until you need to trim large branches. This minimizes stress to the tree.

1. When the tree is still on the small side, choose a leader to be a strong central trunk and trim branches that are beginning to cross it. This optimizes airflow through the tree and keeps it in a healthy state of balance, as well as lending a pleasing aesthetic.
2. Prune the roots once a year or so.

Citrus trees (and fruit trees in general) are very resilient and forgiving of pruning mistakes, so you don't have to worry about making the wrong cut and doing irreversible damage to your tree. The main thing to keep in mind is not to prune the canopy too extensively if your tree lives outside in the summer. Cutting away too many branches can result in too much sun getting to the trunk, and sunburn damage to the trunk. Here's a Youtube video with helpful tips on pruning dwarf citrus and another great video from Luke at MIgardener.

Dwarf citrus can be pruned any time of year.

Harvesting

Limes turn yellow when ripe, just like lemons. Although they are usually used when they are green, they are so much juicier and more flavorful when fully ripe.

It can take a number of months from the time flowers appear to the time when fruits develop, and even longer to harvest. So patience is key.

Ready, set, grow!

Since this post is intended more as an introduction to indoor citrus care rather than a comprehensive guide, there is a great deal that I don't cover here and much that I will explore further in future posts. And, like any endeavor that involves living things, most of what you need to know is learned by trial and error – i.e. just getting your first plants, getting your hands dirty, trying different techniques and seeing what works for you.

If you're ready to dive in, you can order your dwarf citrus seedlings here, or email me at eastnashgreens@gmail.com.

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