Growing garlic in a greenhouse
The greenhouse garlic almanac · Malta
Growing garlic in a greenhouse
A garlic clove is not a button for warmth but a store of time. In a greenhouse, a good crop follows a calm sequence of cool conditions, rooting, leaf growth, longer days, dry ripening and patient curing.
Treat the greenhouse as weather protection, not a machine for endless summer. It keeps heavy rain off the bed, improves control of soil moisture and ventilation, and makes harvesting easier. It must not, however, remove the cool period that supports later clove formation.
01 · The principle
Garlic succeeds under glass when the house protects its natural seasonal rhythm without erasing the cool period that prompts the plant to form a divided bulb.
Garlic seems straightforward: a healthy clove should make a new bulb. Yet its development follows a precise sequence. First the clove makes roots, then enough leaf area. For many varieties, a prolonged cool phase is part of the biological signal. Only the combination of temperature history, rising warmth and longer days starts the bulb dividing into separate cloves.
For this reason, a heated greenhouse is often the wrong first response. Constant warmth may produce vigorous, attractive leaves while the needed cool signal is absent, leaving small or undivided round bulbs. An unheated house, or one protected only from frost, is often more suitable. It offers a dry, accessible bed, controlled watering, less wind and deliberate ventilation without fully cancelling the seasonal pattern.
Start with the variety, then arrange the growing space around it. Hardneck garlic often suits cooler conditions, produces a firm edible flower stalk and usually fewer but larger cloves. Softneck garlic often has more, smaller cloves, can be braided and generally stores longer. These groups are not a complete site recommendation: the individual variety and advice from a reputable Maltese or regional specialist supplier remain decisive.
When planning the whole house for cooler-season crops, include the right model early. Explore the Classic aluminium greenhouse alongside your growing plan. Garlic benefits from a deep ground or raised bed, a clear route for care and harvest, and easy-to-reach vents. Set out rows so tomatoes or cucumbers grown later do not shade the garlic foliage too early in spring.
Before plantingChoose planting stock
Cool seasonCool and root
SpringBuild leaves
Longer daysForm bulbs
Early summerHarvest and cure
Think of this order as a crop clock, not a fixed monthly timetable. Begin with large, healthy planting cloves. Cool soil and moderate moisture encourage rooting; a variety-appropriate cool phase supports later bulb development. In brighter spring conditions, strong leaf area supplies energy for clove division. Finally, reduce watering and growth so bulbs ripen dry and can be lifted cleanly.
Specialist guidance consistently stresses that cool exposure, temperature pattern, day length and variety traits work together in garlic development. The Royal Horticultural Society suggests roughly one to two months at 0 to 10 °C for most varieties. Use this range as guidance, not as a universal refrigerator formula. The exact need depends on variety, origin and prior storage of the planting stock; supplier advice takes priority.
Cooler inland sites
Plant suitable garlic in October or November in a deep, well-drained greenhouse bed. Do not keep the house permanently closed through winter: the crop should still experience natural cool conditions. Roof and glazing protect against persistent rain and abrupt weather changes. After cool, wet periods, still check moisture, as a covered bed can be drier than the outdoor weather suggests.
Mild urban sites
Choose the coolest available area, rather than a position beside a sun-warmed wall. Ask for varieties suited to Malta’s mild conditions. Controlled pre-chilling is appropriate only where the supplier explicitly recommends it. Cooling for too long or at the wrong time can trigger bulb formation before enough leaf area has developed.
Warm, sunny houses
Ventilate early. Even when outdoor air is cool, strong winter or spring sun can quickly raise temperatures under glass. Avoid overheated, humid, stagnant air. A clear central path, openings on more than one side and adequate spacing help release heat and condensation.
Anatomy of a planting clove
Wrapper
Point upwards
Root base downwards
Wrapper. Keep the papery skin as intact as possible. It protects the planting clove from unnecessary drying, bruising and minor injuries.
Shoot tip. Set the narrow pointed end upwards so the new shoot can grow directly towards the soil surface.
Root plate. The flat base faces downwards and makes direct contact with evenly moist, loose soil.
03 · Planting stock
Choose the bulb before choosing the bed.
Planting stock is your first important decision for plant health. Buy certified or specifically sold seed garlic from a reputable specialist rather than random supermarket bulbs. Cooking garlic may come from another climate zone, have been treated to suppress sprouting or carry unnoticed disease into the greenhouse. Use only firm, plump bulbs with dry wrappers. Discard soft, mouldy, damaged, unusually light or dried-out bulbs at the base.
Hardneck
Hardneck, or ophioscorodon garlic, can be a good choice for cooler conditions. It develops a firm central flower stalk and usually a ring of relatively large cloves. Cut young scapes when they curl clearly if large bulbs are the priority. The tender scapes are edible, so you may grow a few extra plants for the kitchen.
Softneck
Depending on the variety, softneck garlic suits milder conditions well. It normally forms no rigid stalk, often has more and smaller cloves, and can be braided after curing. Its storage life is usually better. Reserve particularly strong, healthy outer cloves for the next planting.
Not elephant garlic
Elephant garlic is botanically more closely related to leek and is not true garlic. It is interesting in the kitchen, but its size and cultivation traits are not a sound basis for planning an ordinary garlic crop.
Separate bulbs only one or two days before planting. Ease each clove apart carefully, preserve its dry wrapper and do not damage the flat root plate. This prevents drying and unnecessary entry points for disease. A bruised or deeply split clove is better used in the kitchen than planted into a moist winter bed.
04 · The planting row
Give every clove room for the cool season, roots and its future bulb.
Garlic needs deep, loose soil, not merely a thin layer of rich compost over compacted ground. A permanent ground bed is usually the best greenhouse choice. Where containers are necessary, use broad, frost-resistant pots with at least 25 to 30 cm of growing medium and open drainage holes. Remember that temperature and moisture fluctuate faster in containers than in a deep bed.
Too shallow
Correct
Too deep
Too shallow: An exposed tip can dry out, be pushed up by temperature changes or lose stable anchorage.
Correct depth: Set the tip upwards and cover the clove in a typical greenhouse bed with about 5 cm of loose soil.
Too deep: Planting excessively deep delays emergence and makes growing harder in cold, heavy or continually wet greenhouse soil.
Bed geometry with air
Allow about 12 to 15 cm between cloves and 20 to 25 cm between rows for mature bulbs. A clearly arranged double-row bed uses space efficiently if a wide maintenance path remains beside it. Never step on the root area. Raised beds help where the ground dries slowly, but should not be filled only with loose material that settles heavily by spring.
Before planting, work in some mature compost and improve drainage in heavy soil with suitable mineral material, coarse sand or a raised bed. Soil should retain moisture without becoming waterlogged. Fresh manure and excessive nitrogen are no shortcut: they encourage soft leaf growth and can impair ripening and storage quality.
Planting checklist
- Use the largest healthy outer cloves; small inner cloves belong in the kitchen.
- Point upwards, flat root plate downwards.
- Water thoroughly once to settle the soil, but do not keep the planting row saturated.
- Use only loose, clean mulch and keep it away from young shoots.
- Label every variety and record the planting date and greenhouse position.
05 · The moisture pattern
Water the root zone, not the greenhouse air.
Garlic does not need permanently wet soil. The aim is an evenly supplied, oxygen-rich soil profile where roots remain active from autumn planting to bulb filling.
Establishment
Water sufficiently after planting for soil to settle around the cloves. Then check several centimetres below the surface. A cool covered greenhouse bed often dries slowly in winter even when the upper layer already looks pale and dry.
Leaf growth and bulb filling
As leaf numbers rise, light strengthens and temperatures increase, water demand grows. Water deeply and evenly, without following a rigid weekly schedule. In a greenhouse, rain contributes nothing, while ventilation, sun angle, soil volume and growing-medium structure greatly alter evaporation. Check moisture at root depth. Drip irrigation or slow morning watering directly onto soil is better than wetting foliage. The surface may dry slightly; during active growth, the root zone should not repeatedly dry out completely.
Before harvest
Reduce watering gradually before the intended harvest and, if possible, stop it in the final phase. The aim is moderately dry soil that makes lifting cleaner and shortens curing time, not premature drought stress during bulb filling.
Ventilation is the necessary partner to watering. Open roof and side vents early on bright days so heat and dew do not remain among the leaves. A Classic aluminium greenhouse is especially helpful in late spring, when stronger light rapidly raises temperatures under glass. Plan air movement, clear paths and needs-based watering as one system. Find further model information in the Classic aluminium greenhouse.
06 · Reading the leaves
Bulb problems usually begin earlier.
Do not immediately reach for fertiliser or treatments; first place each symptom in its seasonal context. Garlic is a long crop: the bulb records decisions and stresses that often occurred months before harvest.
Lots of foliage, little bulb
A sufficient cool signal or suitable development time is often missing. An unsuitable variety, very late planting, overheating and excessive nitrogen can also contribute. Check variety suitability and the temperature pattern first. Extra greenhouse warmth cannot replace a missing cool season.
Early yellowing
Check soil moisture first. Waterlogged roots, inadequate supply, disease, pests or normally starting maturity can look similar. Lift one test plant before assuming a nutrient deficiency. Remove clearly diseased plants with their bulbs, and do not add suspicious material to compost.
Small bulbs
Small planting cloves, tight spacing, weed competition, interrupted watering, limited leaf area or bulb formation too early all restrict size. The greenhouse chiefly helps avoid several stresses at once: heavy rain, dry spells and temperature peaks can be managed more deliberately there.
Split wrappers
Split outer wrappers often indicate a late harvest. Once cloves push through their protective layers, storage quality declines. Use these bulbs first. Keep only firm, closed and unblemished bulbs for the following planting.
07 · Lifting at the right moment
The harvest window is narrow and easy to read.
Garlic is not ready while every leaf remains deep green, but it should not collapse completely either. Exact timing depends on variety, site and crop history. Yellowing or drying lower leaves while upper leaves remain partly green are a useful guide. When about one third to one half of the foliage has aged, carefully uncover a test bulb. Individual cloves should be clearly defined beneath tight, closed wrappers without the bulb already splitting.
In Malta, timing for an autumn-planted crop depends strongly on variety, location and temperature history. Under glass, harvest may begin earlier or later. Let the condition of leaves, neck, bulb and wrappers decide rather than a printed calendar month. Plan lifting for a dry spell in both weather and bed.
1
Reduce watering
Gradually reduce watering before harvest and allow the bed to dry moderately. Do not force drought during active bulb filling; this change belongs only to the final stage.
2
Lift, never pull
Loosen soil well below the bulb with a garden fork or narrow hand trowel. Then lift the entire plant with leaves and roots. Pulling by the stem causes bruising or tears at the neck, precisely the damage that shortens later storage life.
3
Do not remove wrappers
Gently shake off only large, loose clumps of soil. Anything more firmly attached may dry first. Do not wash garlic intended for storage or strip away outer layers in harvest enthusiasm. Dry wrappers are the cloves’ natural protection.
4
Separate kitchen garlic and planting reserve
After complete curing, set aside the largest, most even and healthiest bulbs for the next season. This simple selection often improves the coming crop more sustainably than extra equipment or heavier feeding.
The airy curing place
Shade
No direct sun.
No direct sun.
Airflow
Leave space.
Leave space.
Time
Usually two to four weeks.
Usually two to four weeks.
08 · The curing space
Dry for storage, not display.
Freshly harvested garlic is edible, but careful curing turns it into a keeping bulb. Hang whole plants in small, loose bunches or lay them in one layer on an airy rack or slatted shelf. The place should be shaded, dry, rain-protected and well ventilated. A greenhouse is suitable only if it can be reliably shaded and aired. Under closed glazing, direct sun, trapped heat and condensation can make wrappers brittle or reduce quality.
Allow usually two to four weeks. Bulbs are ready when outer wrappers feel papery, roots are dry and the neck rustles when handled. Only then brush away loose soil and trim roots and stems. Softneck garlic can be braided while dry stems remain flexible. Sort again: soft, damaged or conspicuously spotted bulbs should be used first, not stored among healthy ones.
Store fully cured garlic in a dark, dry, airy place, for example in nets, open boxes or loosely hung. Closed plastic containers are unsuitable. The refrigerator is also usually not an ideal long-term place for whole storage bulbs, because humidity and unsuitable temperature changes may encourage sprouting. Storage duration depends on variety, curing quality and room climate; softneck types generally keep longer than hardneck garlic. Check supplies regularly and remove soft bulbs.
For a greenhouse with a clear role across the gardening year, the Classic aluminium greenhouse provides a bright, organised setting for a carefully planned garlic bed in the cooler season. After harvest and thorough bed care, the free space can be used for suitable warm-season follow-on crops or preparation for the next rotation.
09 · Practical questions
Growing garlic in a greenhouse: common questions
Clear answers to choices that strongly affect bulb quality, harvest and storage life.
Can garlic grow in a heated greenhouse?
It can make leaves in a heated greenhouse. Constant warmth does not replace the cool stimulus many varieties need for reliably divided bulbs, however. Use a warm house only for special crops or controlled methods when you know the variety’s needs precisely. For storage bulbs in a home garden, an unheated greenhouse, one protected only from frost, or a deliberately cool section is usually more reliable.
Should I pre-chill garlic cloves in the refrigerator before planting?
Not automatically. With autumn planting in an unheated greenhouse, Malta’s mild winter may not always provide enough cooling naturally for every variety. Controlled pre-chilling may be suitable for certain varieties, but only with a specific recommendation from the planting-stock supplier. Response is variety-dependent; incorrect or overly long chilling can encourage bulb formation too early.
Can I plant garlic in greenhouse containers?
Yes. The container should be broad, frost-resistant and at least 25 to 30 cm deep, with open drainage holes. The crop must still receive the cool conditions it needs. A deep ground bed is more forgiving because it buffers moisture and temperature more evenly. Check containers more often, avoid waterlogging and allow about 12 to 15 cm between cloves for large bulbs.
Should I remove hardneck scapes?
If the aim is the largest possible bulbs, cut young scapes once they curl clearly and are still tender. This leaves more energy for the bulb. The scapes are edible and work well in pesto or vegetable dishes. You may leave a few for observation, but expect those plants to make slightly smaller bulbs.
Why do my greenhouse bulbs stay round instead of forming separate cloves?
An undivided round bulb often points to insufficient cool exposure, a variety unsuited to the site, late planting or too short a period of leaf growth. An excessively warm greenhouse may also play a part. The bulbs are edible. Record the variety, planting date and temperature pattern, then deliberately alter only one factor in the following season.
What crop can follow garlic?
After harvest and careful bed maintenance, the space can be used for warm-season crops, leafy vegetables or a rest and soil-building phase, depending on timing. Do not immediately grow another allium, such as garlic, onion, leek or chives, in the same soil. Multi-year crop rotation and complete removal of plant debris limit the transfer of problems. The Classic aluminium greenhouse offers inspiration for planning the space.
Sources and further reading
Knowledge behind the crop.
More from Bloomcabin: Setting up a greenhouse: layout, plants and care · Water-saving gardening in a greenhouse · Greenhouse curtains and shading
- LWG Bavaria — Garlic: the wonder clove Fundamentals of planting, care, harvest, use and special aspects of growing garlic.
- LWG Bavaria — Vegetables in climate change: garlic German practical experience of cultivation, climate conditions and crop development.
- Royal Horticultural Society — How to grow garlic Guidance on cold requirements, planting time, position, care, harvesting and storage.
- University of Minnesota Extension — Growing garlic in home gardens Specialist information on variety choice, autumn planting, spacing, watering and healthy seed garlic.
- Oregon State University Extension — Garlic (Fall) Practical knowledge on autumn planting, crop care, maturity signs and harvesting.
- Oregon State University Extension — Preserving garlic Recommendations for safe processing, curing and storing garlic.
- LWG Bavaria — Garlic: the wonder clove Further overview of position, planting, care, harvest and use.
