In our bedroom it is citrus season.
It is miserable and cold outside, but our indoor citrus trees are flourishing. They will only move to the terrace again in late April, when overnight temperatures rise above 50'F. These trees have given me so much pleasure, and have prompted so many questions over the years, that I thought I'd share some of my citrus growing tips. There is a lot to tell. Go fetch a cup of coffee. And maybe a sandwich.
Whenever I post a picture of the trees, or fruit, or a cocktail made with fresh-squeezed juice on
Instagram, I am asked questions: "What is wrong with
my citrus tree?" "Why did my Meyer lemon die?" "Why are the leaves on my tree's leaves yellow?" "Why did all my citrus leaves drop off?"
It is impossible to give good answers without knowing exactly how those trees have been cared for. So to help stressed gardeners and to troubleshoot common indoor citrus problems (and to encourage more people to grow citrus trees indoors), I have put together a list of indoor citrus care tips and problems, based on my experiences.
You may recognize your tree's issues, or a care factor you may have overlooked, or not known about.
I bought my first citrus trees, grafted onto dwarf stock, three years ago: two Thai limes (above, at 1st Place). I never dreamed they would make fruit. I would have been happy with their famous, double leaves, to use curries and drinks.
(By the way, if you wonder why I call them Thai limes,
read this post about the k-word).
But by late this year (and after a move) the Thai limes have produced nearly 60 intensely aromatic limes between them. I have been giving them away. Growing a fruit that is close to impossible to buy, even in New York City, is a wonderful experience.
A Meyer lemon and a petite Australian lime (on the windowsill, above), joined the jungle. And that is a bay tree in the foreground. But let's stay focused.
Growing citrus is easier than most of us think. But it does require attention.
Let's begin with the most common problem. By far:
1. Overwatering Your Citrus Tree
Citrus trees will die if overwatered. They
must dry out in between watering. Water deeply, but only water again when the pot is almost dry.
Outdoors, excess water pouring from a pot's drainage holes can just run away. Indoors, the runoff is trapped in a saucer (I never use saucers outdoors - they spell root rot and trouble). Sitting in a puddle of saucer-water for longer than 12 hours is very bad for your tree.
Signs of Overwatering:
If the outside of a terra cotta pot is dark and damp or green at the base, it is a sign that the soil in the bottom of the pot is too wet; the soil stays dark and moist every day, with no change (this means the tree cannot absorb more and is living in an unhealthy, anaerobic environment); water stays standing in the saucer after 12 hours; 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 (harmless) and are an indication that the pots are staying moist enough to grow the fungus they feed on.
2. How to Water a Citrus Tree
Make sure you have a saucer under the pot! Don't laugh. Now drench the pot. This means: give your citrus tree enough water that it runs freely from the drainage hole/s. If no water runs out you have not watered enough. Add more. Take note of how much water you used, for future reference. I use a large measuring jug. My Thai limes drink 10 cups each.
Nancy Lingnan handles customer support at
Lemon Citrus Tree - I bought my Thai limes and Meyer lemon from them - and suggests keeping trees on a stand above a substantial plastic saucer that can accommodate about a gallon of runoff. The water just pours out into the saucer without drowning the tree by letting it stand in a pool.
I don't have stands and giant saucers because of space constraints. Instead, I let any drained water remain in the saucer for up to 12 hours (thirsty trees will absorb this water again). After 12 hours, I suck up all the excess water with a turkey baster (above: an unlikely indoor gardening supertool!). On no account should the water remain longer. You can also use the turkey baster if the saucer is in danger of overflowing.
Only water again when the pot is close to dry. In terms of touch and feel, the top inch or two of soil will transition from dark and moist, to lighter and dry. Time to water. A moisture meter can help you (see Tip No. 5) - I water again when it registers 2 - 3 (Nancy waters again at 4).
With time and experience you will learn how much water is ideal for your own citrus trees. Different rooms, pot sizes, and tree sizes will make it a very personal thing. For example, my Thai limes (almost five feet high), in 14-inch pots, receive 10 cups of water every 5 days* (the moisture meter, poked into three deep spots in the pot, tells me when they are dry).
* Update: with all the fruit harvested from the trees this has turned back into 10 days.
If you suspect overwatering, stop watering. Buy a moisture meter. Allow the soil to dry out. Water only once the pot is almost entirely dry again.
3. Water Temperature for Citrus Trees
Cold winter tap water is a shock for subtropical and tropical citrus trees indoors. If your tap runs icy, take the edge off with a dash of hot water. The water should be roughly the temperature of the room they are in. You could also leave the water overnight in a watering can to reach room temperature.
4. Poor Drainage Kills Citrus Trees
Citrus trees require outstanding drainage. Water must flow right through the pot and out. Soggy bottoms will kill them. Your pots need drainage holes, and a very well-draining soil mixture. (And you don't need shards or gravel in the bottom; this is a myth.)
I mix good potting soil (with no added fertilizer, so skip the Miracle-Gro) with large handfuls of shredded hardwood. A natural cedar mulch is perfect, with no nasty dyes. Softer woods like pine break down too fast. My mix is one-third shredded wood to two-thirds potting soil.
If you have plastic growing pots set inside an ornamental, closed pot, it is imperative that you never allow the citrus to stand in water inside the ornamental pot. After 12 hours, drain it (see No. 1). More work for you, but essential.
Signs of poor drainage: Damp pot bottoms, green algae-like growth on the outside of the pot, constantly moist soil, fungus gnats in the room, yellow leaves, drooping leaves, leaf drop.
5. Underwatering Citrus Trees
It is less common and also less serious than overwatering. Chronic underwatering will kill your citrus trees, but the signs are easier to spot.
Citrus trees need infrequent but
deep watering, so a sprinkle on the surface will not help them. Water the citrus trees deeply till water runs from the drainage holes. Keep a watering diary if you are prone to forgetting.
Signs of Under-Watering:
New, tender growth droops, leaves hang limp; soil pulls away from the sides of the pot; when you water, the water pools clearly on top of the soil for a while before sinking in; once absorbed, the water rushes right through the pot and out (if it does allow the tree to a absorb that runoff from the saucer, then water again).
6. Buy a Moisture Meter
To help take 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. I water again when all three readings in a pot reach 2 - 3. After the drenching it should read 10. If it does not, the water has flowed out too fast because the pot was too dry. Water again right away.
7. Fertilize Citrus Trees Every Month
This is not what most resources will tell you. It's not even what the fertilizer bags and boxes tell you. But professional growers feed often. Indoor citrus trees in pots need more fertilizer than citrus outdoors and in-ground.
In milder winters where citrus trees remain outdoors they slow down in colder temperatures and feed less. But protected indoors, the trees actively grow. In winter I see new shoots, a lot of flowers, and the setting of new little fruit. The energy required depletes the plant, which requires nutrition to stay healthy. Every time you water, food is being made available to your tree, but is also washing out of the soil.
I fertilize organically and feed my citrus trees with Citrus Tone, following the dosage instructions for pot diameter on the bag. Citrus Tone also contains beneficial microbes to help make nutrients available to the plant. Very recently I switched to Down to Earth's Citrus Mix, another organic fertilizer that also includes the micro nutrient zinc - I had a possible and mild zinc deficiency in one of my Thai limes. It's an experiment. I will alternate between the two. Citrus Tone has kept my trees happy for years.
To apply granular fertilizers like these, scratch the fertilizer into the surface soil and water immediately. A light mold can form a few days after fertilizing (with these products); it is nothing to worry about, just scratch it back in.
Signs of nutrient deficiency are diverse: very pale leaves; yellow veins and midrib on the leaves (this may indicate a nitrogen deficiency); green veins with yellow blotches between (could be a zinc deficiency); falling leaves.
Leaves should be a uniform, rich green.
8. Do Not Over Fertilize Citrus Trees
Synthetic fertilizers (like crack-for-plants blue crystal Miracle-Gro) tend to burn plants easily if over-applied. Organic fertilizers are more forgiving. Follow the dosage instructions on the bag, for pot diameter or volume of soil. And avoid fertilizer sticks. They can burn the roots closest to the fertilizer.
Signs of over fertilizing: crisping or burning of leaf edges. Slow or no growth, general malaise, and leaf drop follow.
9. Citrus Trees Need Sunlight (or Very Bright Light)
When we were searching for a new apartment just over a year ago, one of the requirements it had to meet was for a sunny room where the citrus trees could overwinter. Luckily, we found an ideal spot, and our top-floor, south-facing bedroom with lots of windows is home not only to the citrus but to galangal and bay tree. An indoor jungle.
Most citrus trees require six hours of direct sunlight a day (eight is even better but with six you will be fine). A northern winter window will be insufficient (African violets will be happy, though).
If you must keep citrus in a less-than-bright room, boost the light with grow lights. You will need at least a couple per tree. If you have a darker situation, full spectrum lights are very helpful.
But Aaron Dillon, the owner of
Four Winds Growers (where I bought my finger lime) 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; very slow water uptake; green leaves drop from the tree.
10. Too
Much Light Stresses Citrus
We're not talking sunlight. In an excess of zeal, some indoor growers may give the citrus tree 12 hours or more of light, using grow lights. "This causes the plant to go into a vegetative state," says Aaron. Think of them as sleep-deprived. They are very stressed.
Eight hours of grow lights is more than sufficient. The goal is to mimic the natural season as much as possible because the citrus trees have specific seasons of flowering and fruiting. Too much light can interfere with a normal production cycle and limit its ability to produce fruit.
11. Temperature for Citrus Trees
I move my trees indoors when nights dip below 50'F. Most citrus are hardy to colder temperatures and can even stand a brief freeze, but my goal is to maintain their overall, optimum health. This means no shocks. Moving a citrus tree from cold temperatures to heated house is a bad idea, and it may drop all its leaves (this means no food factory for the plant). Move your trees indoors earlier than you may think necessary. Watch the forecast, move them, and keep them indoors for the rest of winter.
Unless you have crazy-high humidity indoors (like a greenhouse), it helps if you keep the nights cool. Our thermostat is set to 60'F overnight. Cooler nights give the trees a sense of chilling, which is necessary for flowers and fruit. (During the day our thermostat is to 65'F but it can reach the lower 70's if I am doing some serious cooking).
Your citrus trees can get too cold indoors. Perhaps your tree is on an uninsulated porch. It may overwinter without dying, but it won't thrive, as cold prevents nutrients from being available to the plant.
Signs of being too hot and dry: spider mites; browning leaf edges.
Signs of being too cold: yellowing leaf veins can indicate that temperatures are too cold for plants to absorb nutrients; major leaf drop.
12. Humidity for Citrus Trees
To raise the humidity indoors I am very low tech: we simply open the bathroom door after showering to let the steam dissipate into the house. (We both shower twice a day so that's four boosts of admittedly temporary steam.)
When the outdoor humidity drops very low in mid to late winter, I mist the air around the trees - and the leaves themselves - daily. I use an entire, small spray bottle. While a Purdue study suggests that misting is close to useless, maybe I mist better?! Or perhaps I just like misting. And, as my dad used to say: Results count. My trees seem to like it.
To increase humidity you can also place the citrus pots on trays of gravel (or on pot feet, or a stand), and keep some water in the saucer, but
never touching the base of pot. This helps raise ambient humidity without drowning the roots.
Or invest in a humidifier. My friend Kevin Espiritu (founder of
Epic Gardening and author of the
Field Guide to Urban Gardening) recommends a Honeywell Cool Mist humidifier “for serious plant parents” to boost humidity levels significantly.
Signs of low humidity: brittle, browning leaf edges; leaf drop. Spider mites.
13. Citrus Trees Hate Drafts and Blasts
Keep your citrus trees away from hot air vents and radiators. Placing them near regular cold drafts, like beside an exterior door, is also not a good idea. Extreme changes in temperature stress citrus. Stressed plants (like people) get sick.
Signs of air stress: browning leaf tips; leaf, blossom and fruit drop (some blossom and fruit drop is normal); spider mites.
14. Scale and Spider Mite on Citrus
Check your trees daily. A little honeydew and a few cobwebs will turn into an infestation (of scale and spidermites, respectively). This is the only time you have to leap into action and invest real time on the trees. The scale above was after a long winter indoors. I found it only as the trees moved outside in May. I had not seen the little suckers on the one side of the tree, which had its back to the window in a deep windowsill.
Luckily, that time, I had help. Migrating common yellow throats snapped up all the scale I had missed.
Indoors, be methodical. If you see clear sticky spots on leaves, inspect your tree all over for scale. Ditto is you see ants rushing up and down (they are attracted to the sweet honeydew). Check along the midribs of the leaves, top and bottom. Scale may also lurk on new growth or thinner branches. Remove scale by crushing with a finger nail (I know, but trust me, you will want to), or swab each scale insect with rubbing alcohol on a cotton bud. I prefer squashing. It is so final.
For a serious scale attack I wash the scale off the leaves with liquid dish soap that contains a degreaser. I use the rough side of a Scotch Brite sponge and even a tooth brush for tricky crevasses.
It takes about 25 minutes to wash an entire tree. In the big scheme of things, how bad is that?
Afterwards, spritz the tree soap-free with a spray bottle of water. Or rinse the whole tree in its pot in the shower (cover the soil with a plastic bag to prevent soap from washing in).
If scale keeps returning, spray the leaves top and bottom with diluted with Neem oil and repeat every three days until the invaders have left. For me this is a last resort, because Neem is just so damn sticky.
If you see the tiny cobwebs on the leaves, you have spider mite. The chances are the room is too hot and dry. Prevention of sider mites is easier: lower the ambient temperature if you can and boost the humidity. Mites love hot dry conditions and we only had them when we had radiator heat we could not control. Try dish soap (with a degreaser) diluted in water to treat the mites. The only really effective treatment I have found is Neem oil, diluted and sprayed on the leaves (top and bottom) and branches.
15. Citrus Trees Lose their Leaves
Although it has never happened to my trees, it is actually common for citrus trees to lose leaves (even all their leaves) when they first transition from outdoors to inside. I think the reason my citrus trees have not lost leaves is because I bring my trees in early, when overnight temperatures dip below 50'F. Technically, you can wait longer as citrus are hardy down to a brief freeze. But the shock of the temperature difference between indoors and out can cause leaf drop. Pay attention to overnight temperatures in early to mid autumn.
A few slightly yellow leaves that drop off can be normal: the tree moves chlorophyll from older leaves (which turn yellow) to new growth or fruit.
If leaves do drop, don't panic and start over-watering or move the tree to another spot. The solution is to pick a sunny window (preferably south-facing away from a heating grate) and stick with it for the whole winter season. Only water when the soil is dry (it will take longer to dry with no leaves to help suck it up). The tree will usually recover.
16. Repotting and Pruning Citrus Trees
Even a dwarf citrus tree will need a larger pot every year or two, just an inch or two larger than its current diameter.
The ideal time to repot is when the tree is dormant, but indoors they keep growing! I repot and root prune around mid winter, after any fruit is harvested, and before blossoms have formed (although there is always some overlap).
My big Thai limes trees are due for a serious prune, top and bottom. I know because they are becoming top-heavy and their pots are drying out much faster than a year ago. At this point I no longer want to keep upsizing their pots because they will become too heavy to carry. To keep the trees from outgrowing their pots I must root prune, and then prune the branches. To prune the roots I pull the whole tree out of the pot (
see how I did it for our fig tree), lay it on its side, trim at about two inches off the rootball all around, and repot with fresh potting soil and cedar bark. I water at once.
The branches must be pruned at the same time, to reduce shock and to manage the size of the tree, of course. I cut them back by one third. There is an art to it and it helps if someone experienced can guide you the first time you do it. Otherwise, always prune at an angle right above a leaf or where another branch joins the one you are removing. Use proper pruning shears.
Signs that you need to repot your citrus tree; the trees need water more often than they used to (because there are more leaves and more roots); leaves begin to drop; the pot feels light for its size (more roots than soil); plants are top heavy and tip easily; roots grow right to the edge of the pot and warp around its interior.
17. The Citrus Pot is Too Big
Overpotting is when a pot is too big for a small plant. The soil-to-root ratio is too high and the roots cannot absorb all the moisture in the soil. This creates damp conditions and as we now know citrus trees hate being wet. In my opinion the ideal pot size is no more than two inches wider (on all sides) than the rootball of the tree.
Signs of overpotting: constantly damp soil; loss of leaves; failure to thrive.
18. Pay Attention
Having you seen the movie
Being There, with Peter Sellars? It's about a gardener but the title (unintentionally, I think) sums up the most important aspect of gardening. Being there.
If you do not check on your citrus trees every day, even when they are healthy, you will not notice changes.
Think of it as forest bathing, and therapeutic. Look at your tree/s. Observe the overall form. Is the tree looking well shaped and perky, or droopy and off? Are the leaves shiny, or dull? Go closer. Yellow leaves? Crisping edges, a few cobwebs? Or just glossy and dark green?
Winter is the time to be watchful.
Signs of citrus problems are diverse. But if you don't see them, you can't address them.
Does this all sound like a lot of work? It can be, a couple of times a year. But tending your little citrus trees has tangible results and genuinely therapeutic value in an age when our attention is focused on abstract screens. Have you ever made lemon blossom bitters, above, with the dropped blossoms after the tiny fruit have formed? You could.
In all my gardening life, I don't think anything comes close to giving me the pleasure of my citrus trees. The perfume of lemon blossom for weeks in the middle of winter, and the reward of waiting for fruit to ripen in its own time, are exquisite.
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