What temperature does a greenhouse need to be for citrus trees?

Aim for roughly 55–65°F during winter. The Chicago Botanic Garden notes most container citrus tolerate down to about 30°F without dying, but 'tolerate' isn't the same as 'thrive' — sustained cold near that floor stresses the tree and triggers leaf and flower drop. A greenhouse that holds 55°F or warmer overnight keeps citrus actively healthy rather than just surviving.

Do citrus trees need extra humidity in a greenhouse?

Yes, and this is the step most growers skip. Citrus originate in humid subtropical climates and struggle in the dry air a heated greenhouse produces in winter — the Chicago Botanic Garden calls supplemental humidity 'essential, especially when the plants are in bloom,' since insufficient moisture causes flower drop and prevents fruit from setting at all. A pebble tray or humidifier matters as much as the heater itself.

Should I fertilize citrus trees in a greenhouse during winter?

No. Citrus are heavy feeders of high-nitrogen, acid fertilizer during active growth, but the Chicago Botanic Garden is explicit that you should not fertilize during winter dormancy. Feeding a slow-growing winter tree mostly builds up salts in the soil rather than getting used, and it's the opposite instinct of the growing-season feeding schedule most citrus-care labels train you to expect.

Why do greenhouse citrus trees get spider mites in winter?

Dry air, not cold, is the usual trigger. A heater keeps a winter greenhouse warm enough for citrus, but the same heat that protects the tree also dries the surrounding air — and spider mites thrive in exactly that low-humidity environment. Growers who add supplemental humidity alongside heat report far fewer mite outbreaks than those who heat without addressing moisture, which is why humidity is treated as a pest-prevention step here, not just a comfort one.

How much light do citrus trees need in a greenhouse?

As much direct light as you can give them — extension and grower guidance both point to a minimum of around 5 hours of direct sun a day, more if you can manage it. Citrus that overwinter in a dim corner of a greenhouse tend to drop leaves and produce little fruit even if temperature and humidity are otherwise correct, since light is the one input a greenhouse structure alone doesn't guarantee.

Growing Citrus Trees in a Greenhouse: Temperature, Humidity & Winter Care Guide (2026)

Quick Answer: Overwintering citrus in a greenhouse means holding 55–65°F overnight, adding supplemental humidity even though the space already feels warm and humid to you, and stopping fertilizer entirely once winter dormancy sets in — all per Chicago Botanic Garden overwintering guidance. The instinct most growers get wrong is treating a heated greenhouse as humid by default: it isn’t, and the dry air a heater produces is the single biggest reason greenhouse citrus develop spider mites and drop flowers before fruit ever sets.

Citrus don’t follow the same rulebook as tomatoes or the tropical side of our greenhouse bonsai guide, where the fix is usually “keep it warmer.” Citrus need warmth too, but the thing that actually kills or stunts a greenhouse citrus tree over winter almost never shows up on a thermometer — it shows up as crispy leaf edges and a spider mite infestation, both caused by air that’s warm enough but too dry.

Greenhouse citrus by the numbers:

55–65°F — the winter temperature band that keeps citrus actively healthy rather than merely surviving. Most varieties tolerate brief dips down to around 30°F per the Chicago Botanic Garden, but sustained cold near that floor triggers leaf and flower drop well before the tree is in danger of dying outright.
5+ hours of direct sun — the minimum daily light most grower and extension guidance recommends for fruiting citrus; a greenhouse that solves temperature and humidity but leaves citrus in a shaded corner still won’t fruit well.
Zero fertilizer in winter — despite being heavy feeders of high-nitrogen, acid fertilizer during active growth, the Chicago Botanic Garden is explicit that citrus should get no fertilizer at all once winter dormancy sets in.

The mistake: assuming a heated greenhouse is already humid

A greenhouse full of moist soil, transpiring plants, and condensation on the glazing feels humid — and during the growing season, for most crops, it usually is. Winter changes that. Running a heater to hold citrus-friendly temperatures dries the air the same way a home furnace dries indoor air in January, and citrus — native to humid subtropical regions — react to that dry heat with crispy leaf margins, flower drop, and a spider mite outbreak that’s often blamed on the cold snap that preceded it rather than the dry heat that followed. Supplemental humidity is “essential, especially when the plants are in bloom,” per the Chicago Botanic Garden, because insufficient moisture is what stops flowers from setting fruit at all — not insufficient warmth.

A humidity tray (a shallow tray of pebbles kept topped up with water, with the pot sitting above the waterline rather than in it) or a small humidifier placed near the citrus bench closes that gap. It’s a five-minute addition most growers skip because a heated greenhouse simply doesn’t look dry — until the spider mites show up.

Why winter fertilizer backfires

Citrus-care labels train growers to feed on a schedule through spring and summer, and that habit is easy to carry straight into winter without thinking about it. The Chicago Botanic Garden’s guidance breaks that pattern deliberately: citrus are heavy feeders of high-nitrogen, acid fertilizer during active growth, but should get none at all during winter dormancy. A slow-growing winter tree isn’t using nutrients the way an actively-growing summer tree is, so winter feeding mostly builds up salts in the potting mix instead of getting absorbed — the opposite problem from an underfed tree, and one that’s harder to flush out of a container than it is to simply avoid.

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Watering and light while dormant

Water only when the soil is dry to the touch during winter — a meaningfully lighter schedule than the consistent moisture fruiting vegetables want. Combined with the no-fertilizer rule, winter citrus care is mostly about doing less, not more, which trips up growers used to the site’s other crop guides where the instinct is usually to add heat, humidity, or feeding. Light doesn’t get a winter pass, though: citrus still want a minimum of around 5 hours of direct sun a day, and a shaded bench position that was fine for a summer crop can leave overwintering citrus dropping leaves even with temperature and humidity both correct.

Before bringing a container citrus into the greenhouse for winter, check it thoroughly for insects — aphids and scale are common hitchhikers, and lightweight horticultural oils or insecticidal soap handle both if caught before the tree is inside sharing air with everything else on the bench.

How to choose

Hold 55–65°F, not just “above freezing.” Citrus tolerating brief dips near 30°F isn’t the same as thriving — sustained cold near that floor triggers leaf and flower drop well before real damage sets in.
Add humidity deliberately. A heated winter greenhouse is drier than it looks; a pebble tray or humidifier prevents both flower drop and the spider mite outbreaks dry heat invites.
Stop fertilizing in winter. Resume only once active spring growth restarts — feeding a dormant tree builds up salts instead of feeding growth.
Don’t let a shaded bench spot undercut everything else. Citrus still needs 5+ hours of direct sun even once temperature and humidity are dialed in.
Inspect before bringing citrus indoors for the season, and treat aphids or scale with oil or insecticidal soap before the tree joins the rest of the greenhouse.

The bottom line

Greenhouse citrus care is really two separate jobs that get treated as one: keeping the tree warm enough (55–65°F, easy for most heated structures) and keeping the air humid enough (the step almost everyone skips, and the one that actually causes flower drop and spider mites). Get both right, stop fertilizing once dormancy sets in, and a greenhouse citrus tree needs surprisingly little else through winter.

Growing succulents in the same structure? Our greenhouse for succulents guide covers a crop that wants the humidity dialed the opposite direction — proof that a single greenhouse often needs more than one microclimate. Curious how citrus stacks up against other tender perennials worth overwintering under cover? Our what to grow in a greenhouse guide covers the light and heat tiers that separate citrus, orchids, and succulents from easier crops.

Still shopping for the structure itself? Our best mini greenhouse and best ShelterLogic greenhouse roundups both cover compact kits with enough headroom for a potted citrus tree.