How to grow mint successfully in a greenhouse
Greenhouse herb growing · Malta
Fresh, long-lived and almost too generous: under cover, mint rewards you with an extended harvest, tender shoot tips and rich fragrance. Its one non-negotiable trait lies below the surface.
The cool flavour zone
How to grow mint successfully in a greenhouse
Give the foliage light, even moisture and moving air. Set firm limits for the roots. This keeps greenhouse mint fragrant, productive and reliably manageable.
01Planting rule: Enjoy the foliage, but contain the roots. A separate, well-drained container for every mint plant is this guide’s key rule.
Why mint thrives under cover
A bright place for flavour, not a jungle for roots
A greenhouse makes mint especially convenient to use. Near the door or central path, it can be picked often, while its pot need not sit on waterlogged soil during wet weather. Young plants are protected from cool nights and heavy rain; spring and autumn harvesting can last longer. Yet mint should not grow in tropical conditions under glass. It needs a bright, well-ventilated position, an evenly moist rootball and pot rims that remain visible and easy to inspect.
Spearmint and peppermint are familiar starting points, but growth habit matters as much as flavour. Most mints spread vigorously through underground rhizomes and trailing shoots. The Bavarian State Institute for Viticulture and Horticulture recommends sufficiently large containers for runner-forming herbs, keeping plants separate and their spread manageable. For one plant, a container around 25 to 35 cm in diameter is a practical starting point.
Treat mint as a container or edging crop, not as a resident of an open greenhouse bed. It needs an accessible watering route, open drainage holes and space from neighbouring plants. For an orderly, airy space with accessible growing zones, the Classic Aluminium Greenhouse provides a suitable basis for clear paths, manageable climate zones and a calm, functional herb display.
Start clean
Three ways to raise your own mint
Mint propagates readily, but a greenhouse should make the start more controlled, not more careless. Use only clearly labelled, vigorous material. Keep out plants with pale speckling, webbing, orange pustules, sticky or distorted tips, or a musty-smelling rootball. With newly purchased plants, a short observation period in a separate area is sensible before they join the herb zone.
Work with clean scissors and fresh, structurally stable compost. Garden soil that compacts is unsuitable for containers and can introduce avoidable problems under cover. A young plant gives the quickest first harvest. Cuttings and divisions are ideal when you want to retain the distinctive scent of a proven plant.
Tip cuttingCut a healthy, non-flowering shoot of 8 to 10 cm directly below a leaf node.— Remove lower leaves and root it in clean water or evenly moist, loose propagation compost.— When several roots have formed, pot individually; keep evenly moist at first, then move to the regular watering routine.—
DivisionRemove a vigorous rootball and separate pieces with their own roots and several young shoots.— Trim damaged roots cleanly and carefully reduce excessive foliage if necessary.— Plant into fresh compost, water thoroughly and protect from intense midday sun until established.—
Purchased young plantBefore moving it inside, carefully inspect leaf undersides, shoot tips, pot rim and rootball for abnormalities.— Gently plant it in its own container of around 25 to 35 cm diameter, not in a mixed herb bowl.— Record the variety and planting date permanently. Labelling helps later with harvesting, division, repotting and spring renewal.—
The realm of runners
Mint finds more than one escape route
The obvious route is a rhizome growing horizontally through the soil. In a greenhouse, subtler routes are added: a shoot hangs over the pot rim and roots in a neighbouring container; roots grow through drainage holes into a damp floor joint; a division ends up in a raised bed; or cut stems are composted where they can grow again. Containment is not excessive caution but a design decision that protects every neighbouring crop.
Choose a sturdy, free-draining pot and place it so that its rim and underside remain visible. Mint should not share soil volume with rosemary, thyme, peppers, seedlings or other long-term crops. A raised planter works only where every variety sits in a separate inner pot and the whole rim can be inspected. An open greenhouse bed is the least reliable solution.
Recommended: separate pot
Possible: closed raised planter
Avoid: open bed
Inspection points: pot rim, drainage holes, saucer, floor beneath the container, neighbouring pots and shoots leaning outward.
Water, light and ventilation
Keep the root zone moist;
Keep the root zone moist;
keep the foliage airy
Water deeply in the pot
Water slowly and thoroughly in the morning so the whole rootball can absorb moisture; excess water must then drain away. Before watering again, check the top two to three cm of compost and lift the pot. Mint copes poorly with prolonged dryness, but a constantly heavy, waterlogged rootball is stressful too.
- Water the compost, not the leaves.
- Use structurally stable compost that holds moisture and drains surplus water reliably.
- Remove standing water from saucers and decorative cachepots.
- Adjust watering frequency for weather, light, pot material, root volume and plant size.
Light and air in the greenhouse
Mint grows well in a bright position but does not enjoy an overheated, still corner. In Malta, glasshouses can become very warm even outside peak summer. Open doors and roof vents early, before heat builds up, and shade lightly if leaf edges suffer or containers dry exceptionally fast. A place near floor level or beside a path is often better than the hottest south-facing side.
- Place pots so foliage does not form a damp, closed wall.
- Ventilate before heat accumulates and leaves visibly wilt.
- In winter, move the pot away from the coldest, persistently wet corner.
- Consider supplementary light only when natural winter light is clearly insufficient for continued growth.
WaterDirectly onto the compost.CheckFeel the compost and assess pot weight.
DrainLet excess water run away.VentilateKeep leaves dry and air moving.
Feeding
Feed, do not force
Mint is grown for aromatic leaves, not a spectacular mass of soft, unstable shoots. Good fresh container or herb compost supplies a new plant sufficiently at first. After several weeks and repeated harvests, a modest dose of organic liquid feed according to the manufacturer’s directions, or some mature compost, may help. If stems become unusually long, soft and dark green, first assess light, heat, crowding, watering and cutting rhythm. The LWG notes that overfed herbs become lush and lose aroma. Restrained, needs-based feeding is therefore better than frequent, heavy fertilising.
A rhythm of renewal
Harvest, pinch and renew regularly
Think of the next growth before cutting
Harvest young shoot tips and cut just above a pair of leaves or a node. This keeps the plant compact and creates new side shoots below the cut. Do not randomly pick individual leaves from the middle, as this leaves long bare stems. With perennial mint, do not remove all foliage every time. Small, repeated harvests on dry mornings usually create a denser, more productive pot than rare, drastic rescue cuts.
Light, repeated tip harvest
Use tender top shoots for drinks and cooking. This routine is harvesting and shaping at once.
New-growth response
New side shoots form below cuts. Turn the pot regularly so the plant does not grow towards the brightest glass on one side.
Periodic rejuvenation
When stems become woody, bare or densely tangled, a harder cut is appropriate. Remove old material, renew the upper compost layer or divide and repot a congested rootball. The aim is young, vigorous shoots that are easy to reach.
Flowers and flavour
Leave some flowers—or cut consistently for leaves
Mint flowers are attractive and often visited by insects, especially when a container is outdoors or accessible through wide-open greenhouse doors. In a crop grown for leaves, many gardeners remove developing flower spikes so culinary mint stays low and branches strongly. For especially aromatic harvests, mint is traditionally cut before full flowering. This need not be a rigid rule: allow one mint plant, kept separately, to flower deliberately and keep the others young through regular cutting. After flowering, cutting back to around 10 cm can encourage new kitchen-ready shoots.
Do not confuse removing flowers with containing roots. Rhizomes and trailing shoots remain the real spread risk. After each care session, inspect the rim, drainage holes, floor and neighbouring pots.
Pests, rust, mildew and hygiene
Make inspection a calm routine
Greenhouse mint is usually straightforward, but early observation pays off in a confined space. Aphids gather on tender tips; spider mites favour dry heat. Fungal diseases become more likely when plants are crowded, leaves stay wet for long periods and air barely circulates. Rust can form orange to rusty-brown pustules, while powdery mildew appears as a pale, floury coating. Treat such symptoms as signs of the whole growing environment, not simply as a reason for a quick treatment.
If a problem occurs, isolate the pot where possible, remove clearly affected plant parts and clean scissors and work surfaces. Improve spacing and air movement. For edible herbs, use only measures and products expressly authorised for the crop and intended use. Follow directions, withholding periods and safety requirements exactly; check Malta’s current plant-protection-product register and label.
01
Young tips
Look for aphids, curled growth and sticky deposits. A small colony may be removed with a gentle jet of water. Inspect repeatedly afterwards rather than assuming a single measure has solved it.
02
Leaf undersides
Look for fine pale speckling, webbing and tiny moving mites. Spider mites are easier to contain before the entire plant looks dusty or bronze.
03
Leaf surfaces
Raised orange-brown pustules suggest rust; a pale flour-like coating may be powdery mildew. Remove affected foliage promptly and open up the plant through spacing and selective cutting.
04
Root zone and tools
Wilting in wet compost, a musty smell or permanently heavy pots suggest root stress. Clean containers before reuse and carefully clean or disinfect cutting tools between suspect plants.
Winter container care and spring restart
Less growth, clearer decisions
The cooler-season rhythm
With shorter days, growth slows and water demand falls. Let compost dry a little more between waterings than in summer, without allowing a small rootball to become completely dry for extended periods. Harvest very sparingly during darker winter weather.
Light without false pressure to grow
Put mint in the brightest practical position. Many varieties are hardy, but roots in pots are more exposed to cold than roots in beds. During an unusual prolonged cold spell in Malta, an insulating base and temporary fleece around the container can help. Keep water and feed aligned with slower growth.
Spring restart
Once new growth gathers pace, renew compost if needed and divide a densely rooted pot. Begin again with restrained feeding and frequent tip harvests. This is also the right time to replace labels, clear drainage holes and inspect every possible route for escaping runners.
For orderly, protected seasonal growing, discover the Classic Aluminium Greenhouse with usable interior space and options for controlled ventilation throughout the year.
FAQ
Questions from the mint bar
Can mint grow year-round in an unheated greenhouse?
Robust mints can overwinter in an unheated greenhouse, but a full harvest all year should not be expected. Growth and yield depend on light, local winter weather and temperatures under glass. In cooler conditions, the plant grows very slowly or may die back above ground before reshooting in spring. Protect the container from unusually cold exposure and waterlogging; water much more sparingly during dormancy.
What pot size suits mint in a greenhouse?
A container around 25 to 35 cm in diameter is a good starting point for one plant. It provides more root space and maintains moisture more evenly than a very small pot, without giving up control of runners. Free drainage holes and visible clearance from the floor matter. If the rootball becomes dense and growth weakens, divide the plant or repot it larger.
Can I plant several mint varieties in one large container?
It is possible, but rarely sensible over time. Strong varieties outcompete weaker ones, roots intermingle and labels lose their practical value. Separating them later becomes laborious. For a collection that remains easy to understand, give each flavour family its own pot. Arranged together, the containers can still look like one considered mint bar.
Why is my greenhouse mint long and unstable?
Long, soft shoots often result from too little usable light, excessive warmth, crowding, heavy feeding or lack of cutting. Improve light and ventilation, cut just above leaf nodes and do not automatically add fertiliser. Turn the pot if every shoot leans noticeably towards one glass surface.
Should I mist mint to increase humidity?
Usually not. Mint benefits more from steady moisture in the rootball and moving air than repeatedly wet foliage. Misting wets leaves but does not remedy a dry centre to the pot. In a dense planting, extra leaf wetness can encourage disease. Water directly onto the compost and ventilate the greenhouse regularly.
How can I stop mint escaping into other pots?
Place every pot so trailing shoots cannot reach compost in neighbouring containers. Inspect the pot rim and drainage holes regularly, and lift the container occasionally. Roots emerging below are removed or managed through division and repotting. Do not carelessly discard rhizomes, divisions and fresh cuttings in greenhouse beds or onto compost where they may grow again.
Sources and further guidance
Sound advice for herb growing
The following specialist sources informed this guidance on plant behaviour, container growing, propagation, harvesting, hygiene and diagnosis. They offer more detail for good cultivation practice.
More from Bloomcabin: Setting up a greenhouse: layout, plants and care · Water-saving greenhouse gardening · Overwintering potted plants in a Bloomcabin aluminium greenhouse
- LWG Bavaria – Fresh herbs from your own garden
- LWG Bavaria – Guide to organic garden growing
- Berlin Plant Protection Service – Healthy culinary herbs in the garden
- University of Minnesota Extension – Growing Herbs in Home Gardens
- University of Minnesota Extension – Powdery Mildew in the Flower Garden
- University of Minnesota Extension – Cleaning and disinfecting garden tools and containers
- LWG Bavaria – Container growing and runner-forming herb characteristics
- LWG Bavaria – Organic gardening, plant health and cultivation care
