How to Grow Shallots in a Greenhouse

Introduction to Growing Shallots in a Greenhouse

I still remember my first attempt at growing shallots outdoors in the UK. It was a wet spring, and half my sets rotted before they even sprouted. That's when I decided to try my greenhouse instead—and what a difference it made! Growing shallots in a greenhouse is honestly a game-changer if you love cooking with these tasty little bulbs.

My greenhouse shallots were ready a good month before my neighbour's outdoor crop last year. The best bit? They were bigger and had fewer problems with rot and pests. You can start them earlier and keep harvesting later, which is brilliant if you use shallots regularly in your cooking like I do.

Shallots are basically onions' sophisticated cousins—they've got a milder, sweeter taste that's perfect when you don't want to overpower a dish. They grow differently too, splitting into clusters of bulbs rather than forming one large one. I've noticed my greenhouse-grown ones tend to form more bulbs per cluster compared to outdoor ones, probably because they're less stressed by weather and temperature swings.

Choosing the Right Greenhouse for Shallot Growing

You don't need some massive glass palace to grow great shallots—trust me! When I started, I used a modest 6x4 greenhouse that sat in the corner of my garden, and it produced enough shallots to keep my family supplied all year. My sister-in-law went for a 6x6 greenhouse because she grows all sorts alongside her shallots, and she swears the extra space was worth it.

When I was shopping for my greenhouse, these features made a real difference for my shallots:

• Good ventilation: My first greenhouse didn't have enough vents, and it was a nightmare for mildew. Make sure yours has windows or vents you can actually open easily.
• Plenty of light: My shallots sulked in a partially shaded spot until I moved the greenhouse to catch more sun.
• Solid construction: My neighbour bought a flimsy greenhouse that blew down in the first autumn gale. Don't make that mistake!
• Shelves or staging: I added these later and kicked myself for not doing it sooner—the amount of growing space it adds is brilliant.

Money a bit tight? Don't worry—some of the cheap greenhouses work surprisingly well. A gardening mate of mine uses the Palram Canopia Hybrid 6x4 and grows cracking shallots. The polycarbonate panels actually help diffuse the light nicely, which stops the plants getting scorched on those rare blazing hot summer days we sometimes get.

I ended up upgrading to a polycarbonate greenhouse after my glass one had an unfortunate encounter with my son's football. The difference in temperature stability was noticeable—my shallots seemed happier with fewer extreme swings between day and night. Just make sure wherever you put it gets good sun, especially in winter when every bit of light counts.

Preparing Your Greenhouse for Shallot Cultivation

Before planting your shallots, proper preparation of your greenhouse ensures optimal growing conditions. Start by thoroughly cleaning your greenhouse to remove any pests, diseases, or debris from previous growing seasons. A solution of horticultural soap or a mild bleach solution (1 part bleach to 9 parts water) works well for disinfecting surfaces.

Next, prepare your growing medium. Shallots prefer well-draining soil that's rich in organic matter. You can use:

• Raised beds within the greenhouse
• Deep containers or grow bags
• Direct planting in greenhouse soil (if you have soil beds)

Whatever system you choose, incorporate plenty of well-rotted compost or manure into your growing medium. Aim for a pH between 6.0 and 7.0, which is slightly acidic to neutral. If you're uncertain about your soil pH, inexpensive test kits are available at garden centres.

Temperature regulation is essential for shallot growth. Before planting, ensure your greenhouse can maintain temperatures between 10-21°C (50-70°F). Install thermometers at different heights to monitor temperature variations. During colder months, you might need additional heating, while summer might require shade cloth to prevent overheating.

Set up an irrigation system that suits your greenhouse setup. Drip irrigation works well for shallots as it delivers water directly to the soil without wetting the foliage, which can help prevent fungal diseases. Alternatively, hand watering with a watering can fitted with a rose attachment provides gentle watering that won't disturb young plants.

Staging or shelving in your greenhouse creates valuable space for starting shallots in modules before transplanting. Position these at a convenient height for working and where they'll receive adequate light. In my experience, setting up a dedicated germination area separate from mature plants helps manage different growth stages more effectively.

Selecting Shallot Varieties for Greenhouse Growing

Choosing the right shallot varieties significantly impacts your greenhouse growing success. Different varieties offer varying levels of disease resistance, storage capabilities, flavour profiles, and growth habits. For greenhouse cultivation, consider these popular options:

Traditional French Varieties:

• French Grey Shallots (Griselle): Offer distinctive, rich flavour but grow more slowly
• Echalion (Banana Shallots): Longer in shape, easier to peel, with excellent flavour

UK-Friendly Varieties:

• Jermor: Copper-skinned with pink flesh, stores well
• Red Sun: Vibrant red-skinned variety with excellent disease resistance
• Golden Gourmet: Reliable producer with golden-bronze skin
• Pikant: Early maturing variety, ideal for greenhouse growing

For greenhouse growing, I prefer varieties that mature relatively quickly and have good disease resistance. The controlled environment allows you to experiment with some varieties that might struggle outdoors in the UK climate. Heritage varieties often provide exceptional flavour but may require more careful attention to growing conditions.

You can grow shallots from either seeds or sets (small bulbs). While sets are easier and quicker to establish, starting from seed gives you access to a wider range of varieties. For greenhouse growing, both methods work well, with seeds typically started in modules before transplanting.

When selecting sets, choose firm, disease-free bulbs about the size of a 2-pound coin. Larger sets are more likely to bolt (produce flowers), which reduces bulb development. For seeds, freshness matters; use seed from reputable suppliers and check the packet date to ensure viability.

In my greenhouse, I've found that growing multiple varieties simultaneously provides a useful comparison of performance under identical conditions. This approach helps identify which varieties perform best in your specific greenhouse environment for future growing seasons.

Step-by-Step Planting Guide for Greenhouse Shallots

Let me walk you through planting shallots in your greenhouse, based on what's worked for me after much trial and error! You've got two ways to start—either with sets (small bulbs) or seeds. Sets are easier and quicker, but I've had great results with both.

Starting from Sets:

1. Pick good ones: I learned this the hard way! Squeeze them gently—they should be firm, not soft or sprouting. Any mushy spots mean trouble.
2. Get the timing right: I usually plant mine in January or February in the greenhouse, though autumn planting works too if your greenhouse doesn't freeze.
3. Don't bury them: Just push them into the soil until the tip peeks out—my first lot rotted because I planted them too deep!
4. Give them space: I space mine about 15-20cm apart. The first year I crowded them, and they produced tiny bulbs.
5. Pointy end up: Sounds obvious, but I've absent-mindedly planted a few upside down, and they grow all wonky!

Starting from Seeds:

1. Module trays work best: I use the same plastic module trays I use for my tomato seedlings.
2. Start early: I sow mine about 8-10 weeks before I want to plant them out. Last year that was early January.
3. Keep them warm-ish: My greenhouse heater keeps them around 15-18°C, which seems perfect.
4. Don't overwater: I killed a whole tray by overwatering once. Just keep the compost damp, not soggy.
5. Wait for the right size: I transplant when they're about 15cm tall and look sturdy enough to handle.

I've become a big fan of starting in modules after my disaster with direct planting. Even the Royal Horticultural Society recommends it, so I'm in good company! The seedlings establish better roots, and there's less shock when you transplant them.

My greenhouse beds get a good sprinkle of horticultural sand mixed in—our clay soil holds too much water otherwise. I learned this tip from my allotment neighbour after losing a crop to rot. Makes a massive difference.

Here's a little trick I stumbled on: after planting, I water them in with a weak comfrey tea solution. Then I add a thin layer of homemade compost as mulch, keeping it away from the actual stems. Stops the weeds and feeds them slowly.

The best thing about greenhouse growing? No more shallots sitting in puddles after those typical British downpours! I can water exactly when needed—usually much less often than you'd think. My outdoor-growing friends are always fighting rot problems that I just don't get in the greenhouse.

Caring for Greenhouse Shallots: Watering, Temperature, and Maintenance

Proper care throughout the growing season ensures healthy, productive shallot plants. In a greenhouse environment, you'll need to pay careful attention to watering, temperature management, feeding, and general maintenance.

Watering Requirements:

Shallots need consistent moisture but dislike waterlogged conditions. Follow these watering guidelines:

• Water when the top 2.5cm (1 inch) of soil feels dry
• Ensure more frequent watering during hot periods
• Reduce watering as bulbs mature and foliage begins to yellow
• Always water at the soil level, avoiding the foliage when possible
• Morning watering allows any splashed foliage to dry during the day

Temperature Management:

Maintaining appropriate temperatures in your greenhouse is crucial:

• Ideal growing temperature: 10-21°C (50-70°F)
• Ventilate on warm days to prevent temperatures exceeding 25°C (77°F)
• Provide shade during the hottest parts of summer
• Consider heating during winter months if growing year-round
• Avoid rapid temperature fluctuations, which can stress plants

Feeding Schedule:

Shallots aren't heavy feeders but benefit from strategic fertilisation:

• Apply a balanced liquid feed every 3-4 weeks during active growth
• Switch to a high-potassium feed (like tomato food) when bulbs begin forming
• Avoid high-nitrogen fertilisers, which produce lush foliage at the expense of bulb development
• Stop feeding approximately 3-4 weeks before expected harvest time

General Maintenance:

Regular maintenance keeps your shallot crop healthy:

• Remove weeds promptly as they compete for nutrients and water
• Check regularly for signs of pests or disease
• Remove any yellowing or diseased leaves
• Ensure adequate spacing between plants for air circulation
• Monitor humidity levels and increase ventilation if condensation forms on greenhouse glazing

From my experience, one of the most common mistakes in greenhouse shallot growing is overwatering. The enclosed environment retains moisture more efficiently than outdoor gardens, so plants typically need less frequent watering. I check soil moisture by inserting my finger about an inch into the soil - if it feels dry at that depth, it's time to water.

Ventilation deserves special attention when growing shallots in greenhouses. Even during cooler months, opening vents for a few hours on mild days helps prevent fungal problems by reducing humidity. In spring and summer, you may need to leave vents open all day and partially open at night to maintain ideal conditions.

Common Pests and Diseases in Greenhouse Shallot Growing

Even in a greenhouse, the buggers still find a way in! Last year I thought my shallots would be perfectly protected, then found tiny thrips all over them. Here's what I've learned about dealing with the most common nasties:

Pests:

Onion Fly: These sneaky devils ruined half my crop the first year. The maggots tunnel into the bulbs, and before you know it, your shallots are rotting.

• Prevention: I now cover young plants with fine mesh—total game-changer!
• Treatment: Once you spot them, it's usually too late. I pull up affected plants straight away and bin them (not compost—learned that mistake!). Sprinkling diatomaceous earth around plants helps too.

Thrips: Tiny little insects you might not even notice until you see silvery patches on leaves. My greenhouse had loads last summer.

• Prevention: I keep everything super clean now and it's made a huge difference.
• Treatment: I bought some predatory mites (Amblyseius cucumeris) online, and they sorted the problem in a few weeks. Yellow sticky traps help too.

Aphids: The green blighters that seem to appear overnight on new growth.

• Prevention: I check my plants religiously now, especially the tender new bits.
• Treatment: My homemade soap spray (bit of washing-up liquid in water) works a treat. My granddaughter loves releasing ladybirds in the greenhouse—they munch through aphids like nobody's business!

Diseases:

White Rot: Absolute nightmare. Looks like white fluff at the base of plants, and once you've got it, you're in trouble.

• Prevention: I only buy sets from trusted suppliers now after a bad experience.
• Treatment: There isn't one, sadly. I had to pull up every affected plant and haven't grown alliums in that part of my greenhouse for years. Eight years is what they recommend!

Downy Mildew: Causes pale patches that turn yellow then brown. Spreads like wildfire when conditions are right.

• Prevention: I keep a small fan running in my greenhouse now to keep air moving. Bit extravagant maybe, but it works!
• Treatment: I cut away any affected leaves immediately. Had to use a copper spray once when it got really bad.

Botrytis (Grey Mould): Fuzzy grey stuff that appears when it's damp and still.

• Prevention: I learned the hard way not to overcrowd—now I'm ruthless with spacing.
• Treatment: Better air flow is the key. I open vents even on cool days now if there's any sign of it.

Neck Rot: Shows up after harvest as softening around the neck. Ruined a whole batch I'd stored.

• Prevention: I make sure my shallots are properly dried now before storing.
• Treatment: Once it starts, that's it—bin job. It's all about prevention.

Sunday morning greenhouse checks with a coffee have become my ritual. Much easier to spot problems early than try to fix them later. I check the leaves, stems, and poke around the soil a bit to make sure everything looks healthy.

I've turned into a bit of a clean freak with my greenhouse—no dead leaves left lying about, tools cleaned between uses, that sort of thing. It's made a massive difference to disease problems. I've also got quite into beneficial insects—my greenhouse has become home to all sorts of helpful creatures that keep pests in check naturally.

For those who prefer organic methods like me, neem oil is brilliant stuff. Smells a bit funny but works on loads of pests. Just don't spray it in the middle of a hot day—I accidentally frazzled some leaves that way. Evening application is much better.

Harvesting and Storing Your Greenhouse-Grown Shallots

Knowing when and how to harvest your shallots ensures the best flavour and longest storage life. Greenhouse-grown shallots typically mature faster than outdoor crops but follow similar harvest indicators.

When to Harvest:

• Harvest when approximately 75% of the foliage has yellowed and begun to fall over
• This usually occurs 90-120 days after planting sets or 100-150 days from seed
• The necks of the bulbs will begin to shrink and dry
• The outer skins will develop the characteristic papery texture
• If you're growing for green shallots, you can harvest earlier when the green tops are 15-20cm tall

Harvesting Process:

1. Choose a dry day for harvesting, ideally after several days without watering
2. Gently loosen the soil around the bulbs using a fork
3. Lift rather than pull the bulbs to avoid damaging the necks
4. Brush off excess soil but don't wash the bulbs if you plan to store them
5. For green shallots, simply pull as needed throughout the growing season

Curing Process:

Proper curing is essential for long-term storage:

1. Lay harvested bulbs in a single layer in a warm, dry, well-ventilated area of your greenhouse
2. Alternatively, hang in bunches with foliage intact
3. Allow to cure for 2-3 weeks until skins are papery and necks are completely dry
4. Trim roots and cut tops to about 2.5cm (1 inch) above the bulb
5. Remove any damaged or soft bulbs for immediate use

Storage Methods:

Once properly cured, shallots store remarkably well:

• Store in mesh bags, braided strings, or open baskets to ensure air circulation
• Keep in a cool (7-10°C/45-50°F), dry place with good ventilation
• Check regularly and remove any bulbs that show signs of sprouting or rot
• Under ideal conditions, properly cured shallots can store for 6-8 months
• Set aside the firmest, disease-free bulbs for replanting if you wish to grow your own sets

I've found that greenhouse-grown shallots often produce larger bulbs with better storage qualities compared to outdoor-grown ones. The controlled environment reduces exposure to excessive moisture during growth and curing, which significantly decreases the risk of storage rots.

For continuous supply, I stagger my greenhouse plantings with about 4-6 weeks between batches. This approach provides fresh shallots throughout the growing season while still allowing for a main harvest for long-term storage. The greenhouse environment makes this succession planting possible even in regions with shorter outdoor growing seasons.

After harvesting, use your greenhouse space for another quick-growing crop. Leafy greens or radishes work well in the post-shallot bed, taking advantage of the remaining fertility while breaking the pest and disease cycle specific to alliums.