Feed an indoor citrus tree with a citrus-specific fertilizer: more in the growing season, less in winter. The RHS: How to grow citrus says to use a high-nitrogen summer citrus feed from late March to October and a balanced winter citrus feed from November to mid-March. The UC Master Gardeners of San Luis Obispo County: Growing Citrus in Pots say to feed about once a month from February through October and not at all in winter. UF/IFAS Gardening Solutions: Citrus says to fertilize four to five times a year once a tree is past its third year.
Those three answers look like a contradiction, but they come from three different growing situations: a UK conservatory, California patio pots, and Florida gardens. This guide lays the schedules side by side, explains why the winter advice differs, and gives a routine for a tree kept in an ordinary home. It also covers the most common reason people over-feed: yellow leaves that are not hunger at all.
The schedules, side by side
| Source | Growing situation | Feeding schedule | Winter |
|---|---|---|---|
| RHS citrus guide | Container citrus under glass or indoors in the UK | Summer citrus feed, high in nitrogen, late March to October | Balanced winter citrus feed, November to mid-March |
| UC Master Gardeners, San Luis Obispo | Citrus in pots, mild California climate | Citrus fertilizer about once a month, February through October | None: feeding in winter can trigger new growth during frost season |
| UF/IFAS Gardening Solutions | Citrus in Florida, including containers | Young trees: light, frequent feedings in the growing season. After the third year: four to five times a year | Not addressed on the page |
| RHS record for kumquat Nagami | Kumquat under glass | Citrus-specific fertiliser through the year, following the manufacturer | Reduced by label, not stopped |
All four agree on one point: use a product made for citrus rather than a general-purpose feed. The RHS and UF/IFAS both name citrus-specific products, and the UC guide says to follow the package directions for a citrus fertilizer.
Why the winter advice conflicts
The California advice has a stated reason. The UC Master Gardeners say winter feeding can push new growth during frost season, and soft new growth is the part of a tree that frost damages first. That reasoning fits an outdoor pot. An indoor tree does not face frost, which is probably why the RHS keeps a winter feed in its calendar, but the RHS changes the product: it swaps the high-nitrogen summer feed for a balanced winter one.
The RHS also says winter is a time of limited light, noting that plants need plenty of light in winter to keep their leaves. None of the opened pages says how light affects how much a tree can use, so a practical reading is a judgment, not a rule: a tree sitting in a dim, cool room in winter has less reason to be pushed, and a balanced feed at or below label strength is the cautious choice. If the tree is leafless, sulking or kept cool for a winter rest, the California advice to stop feeding is also reasonable.
A routine for an indoor tree
- Late March to October: use a summer citrus feed, high in nitrogen, at the label rate (RHS).
- November to mid-March: use a balanced winter citrus feed, or stop if the tree is resting in a cool room (RHS, UC Master Gardeners).
- Young trees: feed lightly but often in the growing season (UF/IFAS).
- After about the third year: four to five feedings a year is a workable minimum (UF/IFAS), while monthly feeding is the upper end described by the UC guide.
- Keep granular products off the trunk: UF/IFAS says never to mound fertilizer against it.
- Do not feed to fix yellow leaves until you have checked water and temperature, as the next section explains.
Before you blame hunger: yellow leaves have other causes
The RHS lists several causes of yellow citrus leaves, and under-feeding is only one of them. The UC Master Gardeners make the same point: yellow leaves can signal nitrogen deficiency, but they may also come from other nutrient problems, overwatering, or cold soil. They add that a little extra iron applied occasionally also seems to help.
| What you see | Causes the sources list | First check |
|---|---|---|
| Yellow leaves | Roots too wet or too dry, draughts, low temperature, under-feeding (RHS); nitrogen deficiency, overwatering, cold soil (UC) | Soil moisture, then the room temperature at the pot |
| Leaf drop | Draughts, winter temperatures too high or too low, too much winter water (RHS) | Position near heaters, vents and cold glass; winter watering |
| Flower drop | Dry roots and low air humidity (RHS) | Humidity, using a damp gravel tray |
| Rotting roots | Overwatering, with leaf fall or yellowing as the first sign (RHS) | Whether the pot is standing in water |
Adding fertilizer to a waterlogged or cold-stressed tree does not solve any of these. Winter overwatering is the commonest problem, according to the RHS, which says to let the compost surface partly dry before watering thoroughly with tepid rainwater. Citrus Leaf Drop Indoors in Winter and Overwatering or Underwatering: Which Drops Flower Buds? go through the water side in detail.
Feeding, flowers and fruit
Fertilizer is not the main trigger for flowering. The RHS says cool or fluctuating temperatures, dry air and cold draughts can cause leaf drop and prevent flowering or fruiting, and that citrus flower on the tips of new side shoots, which is why it warns against over-pruning. A tree that is fed well but kept in dry, draughty air will still drop flowers. If your tree flowers but does not set fruit, see Citrus Flowers but No Fruit.
What the sources do not say
None of the opened pages gives an N-P-K ratio for an indoor tree, a feed strength in grams, or a rule for how much less to feed in low light. UF/IFAS points to a full schedule in its publication HS132, which I did not open. I also could not open the University of Minnesota indoor citrus guide, the University of Maryland dwarf citrus page or the UC IPM fertilizing page, so nothing from them is used here. The micronutrient question, including iron, zinc and boron, is covered only by the UC remark about iron.
Pets and safety
The ASPCA: Lemon lists lemon as toxic to dogs, cats and horses, and the entries for lime, orange and grapefruit say the same. Keep the plant and any feed products out of reach of pets, and read the product label. See Are Citrus Plants Toxic to Cats and Dogs? for the full ASPCA listing.
Frequently asked questions
How often should I fertilize indoor citrus?
The sources give three answers: monthly from February to October (UC Master Gardeners), four to five times a year after the third year (UF/IFAS), and a citrus feed all year with a lighter winter product (RHS). For an indoor tree, the RHS routine is the closest match.
What fertilizer is best for citrus?
A citrus-specific product. The RHS recommends a high-nitrogen summer feed and a balanced winter feed, and does not give a ratio.
Should I feed citrus in winter?
The RHS says yes, with a balanced winter citrus feed from November to mid-March. The UC Master Gardeners say no, because it can trigger frost-season growth. Pick by your conditions: a cool resting tree needs less.
Why are my citrus leaves yellow even though I fertilize?
The RHS lists roots that are too wet or too dry, draughts and low temperature as causes alongside under-feeding. Check those first.
Does kumquat need different feed?
The RHS record for the kumquat Nagami says to use a citrus-specific fertiliser through the year, following the manufacturer's instructions.
Sources read for this page
- RHS: How to grow citrus
- RHS: Citrus problems
- UC Master Gardeners of San Luis Obispo County: Growing Citrus in Pots
- UF/IFAS Gardening Solutions: Citrus
- RHS: Citrus japonica Nagami
- ASPCA: Lemon
Last reviewed 25 October 2026. Written by Md. Firozur Rahman. This page gives general guidance and cannot diagnose a plant from a description; see the Disclaimer. For the whole citrus set, start from the Citrus hub and see Calamondin Indoor Care.
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