Growing lemons and citrus trees in a greenhouse
Classic aluminium greenhouseMalta · Greenhouse Journal
Citrus under glass
Growing lemons and citrus trees in a greenhouse
A lemon tree under glass can become a long-lived container orchard: fragrant, demanding and productive when light, roots, water and winter protection are planned as one system.
The key approach
Greenhouse citrus succeeds when treated as a planned, movable orchard rather than a patio plant brought indoors by chance for winter.
Light drives everything A protected winter position is valuable, but glass alone does not ensure enough light. Place citrus trees in the brightest spot possible and keep glazing clean.
Roots set the pace In a pot, air, water and nutrients are limited. Pot size, substrate structure and watering practice must work together from the start.
Seasonal movement matters In Malta, use the greenhouse as a flexible orangery: ventilated in summer, sheltered during wet or windy spells, and bright with frost protection for rare cold nights.
01 / Choose with foresight
Choose a citrus tree that can remain in a pot
A rewarding citrus collection begins with restraint. A compact, grafted tree from a specialist nursery is usually a better long-term companion than a cheap seedling or a vigorous plant intended for orchard planting. Seedlings may grow attractively, but their characteristics vary and they often take many years to flower. In grafting, the fruiting variety – the scion– is joined to a rootstock that affects vigour, root development, pot suitability and sometimes its response to growing stress.
Lemons
Citrus limon embodies the classic orangery dream: fragrant flowers, useful fruit and, with good care, several stages of development at once. Lemons need abundant light and tolerate neither frost nor persistently cold, wet roots.
Limes
Limes are fragrant, elegant and well suited to containers, but can be more sensitive to cool winter conditions than lemons. Give them the warmest reliably frost-free position in the collection.
Kumquats
Kumquats stay comparatively compact and produce small fruit eaten with the peel. They suit bright, cooler winter quarters, but still need dependable protection.
Calamondin and relatives
Calamondin is a smart choice for smaller orangeries: floriferous, ornamental and bearing tangy, aromatic fruit for marmalade or syrup. Its compact habit makes it especially suitable as a second citrus tree.
Buy with questions, not only a label: Ask for the variety name, rootstock, expected container size and recommended winter protection. Citrus types do not share one temperature limit or growth habit. A clearly labelled, healthy plant makes every later growing decision easier.
02 / Read the trunk
The graft union shows which shoots belong to the canopy
On a grafted citrus tree, find the slightly swollen, angled or scarred point low on the trunk. It must remain visible above the finished substrate surface. Planting too deeply can encourage the scion to form its own roots and makes inspection harder; constant moisture also threatens the trunk base.
Strong shoots below this point come from the rootstock. Remove them cleanly at their base while they are soft and small. Shoots above the graft form the desired canopy and should only be shaped selectively. Citrus stores energy in its leaves and does not benefit from an annual hedge-like cut. Remove mainly dead, damaged, severely crossing or awkwardly upright branches.
Healthy roots need both moisture and air-filled pores, not a permanently saturated pot base. An open, balanced canopy suits the greenhouse: leave room beneath the trunk for watering and allow air to move between leaves. If light mainly comes from one direction, turn the pot a little every one to two weeks during active growth rather than moving it abruptly.
Scion Above the union
Graft union Keep visible
Rootstock shoot Remove below
Roots Need air
03 / The root workshop
A pot that drains, breathes and stays movable
A citrus container should buffer summer heat and rapid drying, yet exceed the existing root ball only moderately. Putting a small tree straight into a huge pot leaves a broad zone of unrooted substrate that stays wet for too long. Roots cannot quickly occupy it; oxygen shortage, weak growth and root damage become more likely.
Repot preferably shortly before strong spring growth and usually choose only the next pot size. Many mature container citrus trees manage long-term with a 60–95 litre container ; compact varieties need less and vigorous ones more. Large clear drainage holes, a wide stable base and a wheeled saucer or plant trolley that safely supports the fully watered pot are crucial.
Use high-quality, structurally stable container compost rather than heavy garden soil. A mix of organic material for water and nutrient retention with coarser mineral or structural components for air pores works well. The goal is not a decorative gravel layer at the base, but a root zone that drains evenly and promptly from top to open outlets.
Container hydrology
Pot and root ball
Water slowly
Moisten the root ball
Keep air pores
Keep drains clear
A correctly sized pot lets excess water run away promptly, then dries gradually. An oversized container often remains wet too long; a fully rooted pot can dry out quickly. Water evenly until a little drains below, and never leave the pot standing permanently in a full saucer or cachepot.
04 / Water by observing
Water the root zone – then read the tree’s response
A fixed weekly routine is rarely precise enough for greenhouse citrus. A sunny June week, a dull December spell, a newly repotted tree and a densely rooted pot use entirely different amounts of water. Check several centimetres into the substrate, note pot weight and use leaf appearance as confirmation, not the only signal.
1. Check→
2. Water→
3. Drain→
4. Adjust
Check: Feel below the surface. Water when the top layer has dried slightly but the inner root ball is not yet dust-dry.
Water: Water slowly, preferably in two passes, until a small amount emerges below instead of dampening only the surface every day.
Drain: Empty saucers and cachepots, and check that drainage holes remain clear. Citrus does not tolerate continually saturated roots.
Adjust: Increase frequency in heat and active growth; reduce it as winter light, temperature and growth decline.
Water quality and feeding
Very hard or alkaline water can gradually raise substrate pH and restrict trace-element availability, especially iron. Do not answer every pale leaf with more fertiliser. First assess moisture, root condition, recent temperature or position changes, pests and the precise discolouration pattern.
Feed regularly but moderately during active growth with a citrus fertiliser containing trace elements. Follow the manufacturer’s dose; smaller, steady applications are usually better than rare heavy ones. In cool, low-light winter conditions, feed far less or not at all. If water leaves heavy lime or salt deposits, clean rainwater or a mix with tap water may be practical. Flush only free-draining substrate.
Read leaves before feeding
Even yellowing
Green veins
Brown edges
Bronze patches
Speckling
Even yellowing can relate to ageing leaves, weak light, wet roots, exhausted compost or general nutrient shortage.Green veins on pale leaves may indicate limited trace-element availability, sometimes worsened by high pH.Brown tips can result from salt build-up, dry roots or excessive fertiliser.Watery or bronze areas fit cold, heat or sun damage.Specks, webbing or sticky surfaces need a close pest inspection.
05 / The flower room
Flowers are a promise, not an instruction to overload
Pollination
Many common citrus varieties are self-fertile and can set fruit without a second tree. Air movement and occasional insect visits help transfer pollen. In a very enclosed winter space, a soft brush can help: move it gently from one open flower to the next during the morning. Do not routinely treat every flower. First see whether the tree sets fruit reliably unaided.
Fruit set
Some young fruit drops naturally. After a change of position, or with root stress, low light, drought or overwatering, the tree often reduces flowers and fruitlets to rebalance itself.
Patience
Keep water and nutrient supply as steady as possible while flowering and avoid heavy pruning then. If a young or weakened tree carries too many fruitlets, remove some so canopy and roots can continue building strength.
Citrus can carry flowers, young fruit and ripe fruit at the same time. That picture makes growing under glass so appealing – and explains why stability matters more than constant intervention. Sudden heat, cold draughts, prolonged dryness, saturated roots and abrupt light changes can cause leaf or fruit drop. Stabilise conditions before feeding in haste.
06 / The protected season
Summer ventilation and winter warmth belong to one climate plan
A glazed greenhouse amplifies the weather. In summer, citrus trees often need roof ventilation, open doors, temporary shade and moving air long before the garden feels uncomfortably hot. In winter, the same structure needs a deliberate plan: abundant light, dependable frost protection and watering matched to the plant’s much slower metabolism.
Summer: prevent heat build-up
- Ventilate early. Roof vents, automatic openers and, if needed, gentle air circulation prevent stagnant heat among the leaves.
- Use temporary shading in intense sun, especially after moving a tree from a darker location into the greenhouse.
- Acclimatise citrus gradually to outdoor sun or stronger light under glass. Sudden change can scorch leaves and trigger leaf drop.
- Avoid placing pots on intensely heated surfaces and check root-ball moisture more often during summer heatwaves.
When planning a citrus orangery, consider ventilation, shading, movement space and watering together from the beginning. A useful starting point is a classic aluminium greenhouse with considered height and easy-to-reach openings.
Winter: cool, bright, protected
Lemons and limes are particularly frost-sensitive; some kumquats and other citrus forms tolerate cooler conditions depending on variety and rootstock. Malta’s winters are generally mild, but an unheated greenhouse is still not a blanket guarantee for a lemon tree during unusual cold spells. Monitor the real minimum temperature and arrange insulation, supplementary heat or timely relocation before cold arrives.
The winter envelope
TemperatureAvoid frost reliably
LightBrightest position
WaterLess often, thoroughly
AirVentilate gently
Base winter protection on the most sensitive tree in your collection instead of relying on one temperature for every citrus type. Keep glazing clean and avoid unnecessary shade. Low winter light limits how much water and fertiliser the tree can use. Water less often, but deeply when needed. Ventilate briefly on mild days to reduce high humidity without creating persistent cold draughts.
If the greenhouse is to support citrus through Maltese winters, enclosed volume, usable height, ventilation and technical equipment all matter. A classic aluminium greenhouse provides a solid basis for a site-specific orangery plan. Allow broad routes for heavy wheeled pots, accessible roof vents and, where appropriate, suitable glazing or heating options. Place sensitive trees where temperature, root balls and pests can be checked easily – not only for visual symmetry.
07 / Diagnose first, act second
Five citrus problems worth a calm check
Root alert
Leaves yellow while the substrate stays wet
Pause feeding. Check drainage holes, pot weight, smell and root condition. Improve watering intervals and drainage before assuming the pattern is a nutrient deficiency.
Light alert
Long soft shoots and few flowers
Light is usually the first point to check. Move the tree brighter, clean the glazing and avoid nitrogen-heavy feeding that promotes more soft growth.
Pest alert
Sticky leaves or dark coating
Inspect shoots and leaf undersides for scale insects, mealybugs, aphids or other pests. Isolate the plant where possible, clean it mechanically and improve airflow and inspection routines.
Salt alert
Dry leaf edges despite regular feeding
Fertiliser salts can build up in the container. Flush with suitable water only if the substrate drains freely. During active growth, feed more lightly but more regularly afterwards.
Temperature alert
Leaf drop after a cold night or summer heat spell
Check maximum and minimum readings with a reliable thermometer at canopy level. Stress events are often evident in the temperature record, not on one leaf. Optimise ventilation, shading or frost protection before making major pruning or feeding changes.
08 / A year under glass
The annual calendar for container citrus in Malta
Treat this calendar as a rhythm, not a substitute for actual weather. The season may begin earlier or later according to location, exposure and greenhouse conditions. A sunny outdoor position can be ideal in settled weather; the greenhouse then provides shelter during wet, windy or cooler periods.
January–February Protect from unusual cold, maximise light, water sparingly and check regularly for scale insects, mealybugs or spider mites. Do not force soft winter growth with heavy feeding.
March–April Feed moderately as new growth begins. Repot or work on roots only if the root ball is dense. Open roof vents early on sunny days.
May–June Check and water more often as growth increases. Acclimatise gradually to direct sun when moving outdoors. Watch flowers and early fruit set closely.
July–August Prioritise shade, air exchange and even root-ball moisture. Continue moderate feeding during active growth. Check pots and foliage daily during heatwaves.
September–October Plan a move under glass before wet or windy conditions become stressful. Acclimatise trees gradually to lower light and inspect for pests before bringing them in.
November–December Activate the winter plan, clean the glazing, reduce watering and monitor real overnight lows at canopy height and around the root zone.
Every month Remove rootstock shoots, turn pots occasionally for balanced growth, clean dusty leaves and harvest fruit by typical variety size, fragrance, slight softness and flavour.
With every change If leaves react, first trace recent changes in light, temperature, water, feeding, humidity or position before making another intervention.
For greenhouse architecture that supports this seasonal rhythm, explore a classic aluminium greenhouse and review the equipment options for a classic aluminium greenhouse. A citrus orangery needs clear circulation routes, room for wheeled bases, accessible water, effective ventilation and enough headroom for a mature canopy. Plan door width and turning space around the heaviest pot – not only the young plant at purchase.
Questions from the citrus bench
Frequently asked questions about greenhouse citrus
Can a lemon tree overwinter in an unheated greenhouse?
Only if the greenhouse stays reliably above damaging temperatures for that particular plant. Malta is generally mild, but an unheated house is not an automatic winter guarantee for lemons or limes during exceptional cold. Measure temperature at the canopy and root zone, and plan extra protection, heat or an alternative location before cold weather arrives.
Do greenhouse lemons need a second tree for pollination?
Many common container citrus species and varieties are self-fertile. A second tree is usually unnecessary. In a very enclosed space, gentle air movement or a soft brush can support pollen transfer.
How often should citrus be watered in a greenhouse?
There is no universal interval. Water according to substrate moisture, pot weight, season, light and temperature. The aim is evenly moist, well-aerated roots – not a permanently wet surface.
Why does the tree lose leaves after being moved?
Citrus often reacts to abrupt changes in light, temperature and humidity. Acclimatise the tree over several days, keep watering steady and do not combine relocation with repotting, heavy pruning and strong feeding.
Must a citrus tree be pruned every year?
Prune lightly and purposefully. Remove dead wood, rootstock shoots, strongly crossing branches and shoots that disrupt the desired structure. Avoid radical annual cutting.
When is it too hot for citrus in a greenhouse?
Warning signs include wilting foliage despite adequate root-ball moisture, scorched leaf areas or indoor readings that remain far above outdoor temperature. Open doors and roof vents early, improve air movement and use temporary shade before peak midday heat.
Sources and further reading
A sound citrus library
These expert resources explore container growing, watering, nutrition and overwintering. They help adapt general advice to the variety, rootstock, water quality and local winter conditions. For valuable or diseased plants, advice from a specialist nursery is also worthwhile.
More from Bloomcabin: Made-to-measure aluminium greenhouse · Classic aluminium greenhouse · Sizes, glazing and options for aluminium greenhouses
- North Rhine-Westphalia Chamber of Agriculture – overwintering container plants correctlyGerman practical advice on bright, cool, frost-free winter quarters for sensitive container plants.
- North Rhine-Westphalia Chamber of Agriculture – container plant bookletA compact overview of location, care and overwintering for container plants needing protection in Germany.
- Mississippi State University Extension – Growing Citrus in ContainersFundamentals of free-draining substrate, appropriate pot size, watering and nutrient supply for container citrus.
- Texas A&M AgriLife – Citrus Fact SheetExpert information on grafting, light, container culture and correctly applied watering for citrus trees.
- University of Florida IFAS – Citrus Nursery Production GuideTechnical background on irrigation control, substrates and nutrient management in protected citrus production.
- University of California IPM – Cultural Tips for Growing CitrusLinks between watering, feeding, canopy care, pests and the long-term health of citrus plants.
Room for an orangery
Give citrus the winter space it deserves.
Plan headroom, bright glazed surfaces, effective ventilation and a clear route for wheeled pots through every season. This creates more than shelter for a lemon tree: a cultivated orangery that brings fragrance, flowers and fruit into the Maltese garden year.
Classic aluminium greenhouseFurther options for a long-term orangery are offered by the classic aluminium greenhouse– a thoughtfully planned space for plants that stay and grow over the years.
