Indoor citrus trees are trendy. The proliferation of portable trees—grafted onto dwarf rootstock—makes it possible for almost anyone to grow a lemon, lime, or kumquat without having a large space.
With their rise in popularity comes the challenge of citrus care, especially in climates with hard winters, when the subtropical trees must overwinter indoors for months in conditions that can be stressful to the plants (and sometimes to their owners). Indoor conditions are challenging, with lower humidity, higher and drier heat, and more difficult watering protocols. Unsuspected problems can build up sneakily, surprising us and threatening the trees we love.
Read on to learn what those indoor citrus issues might be, and how to prevent or fix them.
Photography by Marie Viljoen.
1. Poor drainage kills citrus trees.
Citrus trees require outstanding drainage. Soggy bottoms will kill them. Water must flow right through the pot and out. I mix my potting medium with large handfuls of shredded cedar mulch or cedar shavings. My mix is 50:50 potting soil and wood. The pots have a large drainage hole in the bottom and stand on feet in saucers. If your pots are set in an ornamental, closed pot, it is imperative that you never allow them to stand in a pool of water. If the water stands for more than an hour, drain it (see No. 2). More work for you, but essential.
Signs of poor drainage: damp pot bottoms, constantly moist soil, fungus gnats in the room, yellow leaves, drooping leaves, leaf drop.
2. Overwatering can kill citrus trees.
Overwatering is the most common cause of their poor indoor citrus tree health. Do water deeply, but only water again when the pot is close to dry. If water in my trees’ saucers touches the bottom of the pot, I let it remain in the saucer for up to an hour hours (thirsty trees will absorb this water again). But after that I suck up excess water with a turkey baster (yes, really).
I also like to use terra cotta pots. If the outside is dark and damp at the base, this is a sign that the soil in the bottom of the pot is too wet (even if the top is dry), which is not good, so I hold off on watering. In terms of touch and feel, the top inch or two of soil will also transition from dark and moist to the touch to lighter and dry. Time to water.
Signs of overwatering: the soil stays moist every day; the bottom of a terra cotta pot looks dark, or green, and is damp to the touch; water stays standing in the saucer; the leaves are drooping, but not dry and crisp; the leaves gradually turn yellow all over and drop; little bugs like fruit flies hover everywhere – these are fungus gnats and are an indication that the pots are staying moist too long.
3. Citrus trees need deep watering.
Nancy Lingner, who provides customer support at LemonCitrusTree (her daughter, Crystal Kim, owns the business) recommends that you drench the pot and “drown the soil” allowing the water to run freely from the drainage holes. To do this, Nancy likes to keep trees on a stand above a substantial plastic saucer that can accommodate one gallon of runoff. (Because of space constraints my set up is more modest.)
She reiterates that “a few cups here and a few cups there” are ineffective, for watering. Establish a schedule, but be prepared to flexible. For example, I water once every seven to ten days.
Signs of under-watering: the soil pulls away from the sides of the pot; when you water, the water sits on top of the soil for a while before draining; water runs quickly through the pot and out; the leaves droop, and turn crisp; branches die.
4. A moisture meter can save a citrus tree’s life.
To help take some of the stressful guesswork out of watering citrus, buy a moisture meter. Insert it fully into the growing medium. In larger pots it is helpful to take two to three readings in different spots.
5. Citrus shiver with winter-cold water.
Their water should be tepid or at roughly the temperature of the room they are in. I mix a splash of hot water with cold tap water, in a large measuring jug.
Signs of freezing water: yellowing leaf veins can also indicate that temperatures are too cold for plants to absorb nutrients; leaf drop. (This may also indicate that the room is very cold.)
6. Citrus trees love nitrogen.
Indoor citrus trees stay hungry in winter, and they love nitrogen. In milder climates where they overwinter outdoors they slow down and feed less, but not inside, where it’s warmer. Winter is when I see a lot of flowers appearing and the setting of new little fruit; the energy required depletes the plant, which requires nutrition. Well-draining pots also means food washes out quickly. Every time you water, food is being made available to your tree. I feed my trees monthly with Citrus Tone, following the dosage instructions on the bag. Water immediately after fertilizing. You can also foliar feed in your shower or bath with a sprayed solution of liquid seaweed or fish fertilizer (the smell will take about eight hours to dissipate).
7. Sat no to fertilizer sticks.
Avoid using fertilizer sticks in citrus pot. They can burn the trees’ roots. Using organic fertilizers decreases the chances of damaging your plant (and boosts biodiversity within the soil). If you must use synthetic fertilizer, never exceed the recommended dose.
Signs of overfeeding (usually with synthetic fertilizers like the blue crystals): burned edges to leaves; leaf drop; very slow growth.
8. Citrus trees need very bright light.
When we move, I look at every potential new apartment through the eyes of my citrus trees. Is there outdoor space, and is there be enough light for them indoors in winter?
When I first saw our current apartment, I walked into the top-floor space (after weeks of searching) and was greeted by skylights and ample southern windows flooded with sunlight. This was it (even if there were not enough closets). There is a little wiggle room: whereas a Meyer lemon is uncompromising in its need for a minimum of six hours of sunlight, trees like Thai limes, finger limes, and calamondin are less demanding, because they evolved in semi-shady forest conditions. Very bright, indirect light will keep them healthy, although they will produce fewer flowers and fruit.
A targeted full-spectrum grow-light can help that persnickety Meyer lemon, although Aaron Dillon, the fourth-generation citrus grower and owner of Four Winds Growers in California, says that in cases where a tree receives “at least some natural sunlight” during the day, “a simple T-2 fluorescent can provide enough supplemental light.”
Signs of low light: poor growth; green leaves drop from the tree.
9. Too much artificial light can stress indoor citrus.
Who knew? Citrus trees can have too much light. Aaron Dillon says that the mistake some people in northern climates make is to give the tree 12 hours or more of supplemental light, “which causes the plant to go into a vegetative state.” Think of them as sleep-deprived.
Eight hours of light is more than sufficient. Aaron points out that the goal is “to mimic the natural season as much as possible” because the citrus trees have specific seasons of flowering and fruiting. “By exposing the tree to too much light it can interfere with its normal production cycle and limit its ability to produce fruit.” It helps if you keep the nights cool. In our house the thermostat is set to 64 degrees Fahrenheit overnight (it saves on heating bills, too).
10. Citrus trees need to moisturize as much as you do in winter.
Indoor winter air is notoriously dry. We moisturize, but what can our trees do? Misting the trees daily with a spray bottle helps (wash the bottle every week). But if you want to cut down on the time spent misting, invest in a humidifier. Kevin Espiritu, the founder of the website Epic Gardening and author of Field Guide to Urban Gardening (Cool Springs Press, May 2019), recommends a Honeywell Cool Mist humidifier “for serious plant parents” to boost humidity levels significantly.
Signs of low humidity: brittle leaf edges; leaf drop, spider mite cobwebs.
11. Citrus trees hate a draft, and a radiator blast.
This is not easy in apartments where the heat source is near that light-giving windows. But do your best. Do not expose citrus trees to cold drafts, either. Opening the nearby door or window for them on a cold day stresses citrus trees (and all plants). Stressed plants are susceptible to diseases and pests.
Signs of air stress: browning leaf tips; leaf, blossom and fruit drop.
12. Daily wellness check.
Make it a ritual (consider it citrus-bathing, and therapeutic). Observe the overall form. Is the tree looking well shaped and perky, or droopy and off? Go closer and look at leaves, turning them over. Are they green and upright, or beginning to yellow? A few slightly yellow leaves can be normal as the tree moves chlorophyll from older leaves to new, but perhaps it is underfed, or overwatered. If you see tiny cobwebs on leaves you may have the beginning a spider mite infestation. Is there shiny, sticky honeydew on some leaves or the surface under the tree? You have scale. Ugh.
As Nancy Lingner wrote to me in an email: “Where can a pest go for food in the middle of a Montana snowstorm? If you were a pest it would be a dream come true observing a scrumptious citrus tree just sitting there indoors in a warm environment.” Winter is the time to be watchful.
Signs of neglect: honeydew from scale, sooty mould, cobwebs, dropping and drooping leaves, yellow leaves.
13. Don’t expect citrus tree problems to disappear on their own.
Problems will not resolve themselves. A chronically overwatered tree will die. A little honeydew and a few cobwebs will turn into an infestation. You will find scale insects on the undersides or topsides of the leaves’ midribs: squash them with your nails. You can also wash them off the leaves with a de-greasing liquid dish soap, using a sponge and a tooth brush for tricky crevasses. Spritz the tree soap-free with a spray bottle of tepid water or rinse off in the shower if you can lift the pots. If the issue is serious, spray with Neem oil and repeat every three days until the invaders have left.
Signs of ignoring your trees: honeydew all over the tree and surfaces; cobwebs; general malaise, depending on the source of the issue.
14. Panicking at leaf loss
“When it starts to happen,” Aaron writes, “people usually panic and start over-watering their tree (the biggest no-no with citrus)” or they move it to another spot. The solution is to pick a sunny or bright window and keep it there for the rest of the winter season. “If the tree loses some leaves (even all its leaves) don’t panic. As long as they don’t over water the tree, it will usually recover.”
Does this all sound like a lot of work? It is. But tending your little citrus trees has tangible results and genuinely therapeutic value in an age when much of our attention is focused on screens. The reward is exquisite and engages all our senses: Being able to smell citrus blossom in our homes in winter, and to pick and eat fragrant leaves and ripe fruit from our very own trees.
See more growing tips in Lemon Trees: A Field Guide to Planting, Care & Design in our curated guides to Edible Plants 101. Read more:
- How to Keep an Indoor Citrus Tree Happy
- Gardening 101: Thai Lime Trees
- The Truth About an Indoor Lemon Tree (Hint: It Belongs Outdoors)
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