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Greenhouse Growing Guide
by Matt W (Greenhousestores)
Key Takeaways
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Greenhouses extend the growing season by creating a controlled environment for year-round gardening in the UK
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Proper ventilation is essential to prevent overheating and reduce humidity that can lead to plant diseases
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Choose the right location with maximum sunlight exposure (south or southeast facing) for optimal plant growth
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Start seeds earlier than outdoor planting dates to get a head start on the growing season
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Small greenhouses work well for limited spaces and are perfect for beginners or those with smaller gardens
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Water plants in the morning to allow foliage to dry before cooler evening temperatures
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Monitor temperature regularly using a min/max thermometer to maintain ideal growing conditions
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Use staging and shelving to maximise growing space and improve organisation
Key Takeaways
- Greenhouses extend the growing season by creating a controlled environment for year-round gardening in the UK
- Proper ventilation is essential to prevent overheating and reduce humidity that can lead to plant diseases
- Choose the right location with maximum sunlight exposure (south or southeast facing) for optimal plant growth
- Start seeds earlier than outdoor planting dates to get a head start on the growing season
- Small greenhouses work well for limited spaces and are perfect for beginners or those with smaller gardens
- Water plants in the morning to allow foliage to dry before cooler evening temperatures
- Monitor temperature regularly using a min/max thermometer to maintain ideal growing conditions
- Use staging and shelving to maximise growing space and improve organisation
What can I do in my greenhouse all year?
Greenhouse Growing Month by Month in the UK
Our Greenhouse Growing Guide gives a month by month guide on what to grow and when. A greenhouse allows you to grow vegetables all year round. It's a great place to start for Greenhouse Beginners.
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November/December
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January
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February
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March
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April
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May
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June
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July
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August
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September
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October
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Plant Selections for a New Greenhouse
A greenhouse is a piece of garden infrastructure that serves many horticultural functions: it can be an "orangery" for potted plants that aren’t quite winter hardy, a summer home for crops that need a bit of extra heat, and a sheltered space to start all kinds of new seedlings for the season.
For the gardener looking to get a head start on cultivation during the cooler months of spring, there are a variety of plants that can be easily germinated and cared for through the seedling stage in a greenhouse.
Below is a list of some of the more easy to grow selections for spring germination in a greenhouse.
Brassicas & Other Leafy Greens
Brassicas are plants in the cabbage family. Generally, they are coolweather crops, and will germinate even when soil temperatures as low as 10C. Therefore, they are some of the first plants that can be started in a greenhouse, in late winter or early spring (depending on the current and expected temperatures of the year).
"Leaf vegetable" on the other hand is kind of catchall term for plants that are grown for their leaves, belonging to a wide variety of botanical families: not just brassicas. Lettuces, for example, are in the A steraceae (daisy or aster) family.
After being planted in seedling flats and growing their first set of "true leaves", most brassicas and leafy greens can be moved out to a cool or covered section of the garden.
Brassicas to grow:
Asian Greens
Asian vegetables like pak choi (also known as bok choy), chinese or nappa cabbage make a tasty addition to a stir fry.
Broccoli
Most broccoli purchased in stores is a single cultivar: calabrese broccoli. From seed, however, gardeners have an array of options: purple sprouting broccoli, for example, gives a flower head full of dark and antioxidant anthocyanin pigments.
Brussels Sprouts
Growing up the stalk of the plant, these "mini-cabbages" are an attractive and healthy addition to the garden.
Cabbage
A classic of European cuisine and gardens, both red and green cabbages are experiencing something of a culinary renaissance, owing to their extremely rich profile of vitamins, minerals, and antioxidants, and long shelf life.
Kales
Classed as a superfood, kales are also extremely ornamental: cultivars like "Red Russian" and "Dinosaur" like grow into attractive palm-shaped plants that can be harvested all summer long.
Leafy greens to grow:
Chard
Closely related to beets, chard is a pleasantly earthy-tasting leaf vegetable. Cultivars like “Rainbow” boast brightly-coloured stalks, coming in shades like pink, red, orange, yellow, and white.
Endive
A bitter favourite of Italian cuisine, endive or chicory can be sown in a greenhouse in spring, but perpetually cultivated as a perennial thereafter, as it re-grows from a thick taproot. Come harvest time, it is best served sautéed.
Lettuce
Lettuce is a crop that goes so far beyond what is seen in supermarket shelves: fresh-plucked greens don’t need to be selected to shelf life, so heirloom or exotic cultivars like the bright red and curly-leafed "Galactic Lettuce" are perfect for the home gardener.
Spinach
Originating in Asia, this classic Amaranth-family green is loaded with nutrients and can be plucked from all summer long.
Cucurbits
Belonging to the botanical family Cucurbitaceae, these vining plants are often sown indoors, and transplanted out (or to a permanent, larger pot) once they have their first set of true leaves.
Care should be taken not to sow them too early in a greenhouse, because after they grow to a certain size, they don’t like being transplanted. They are best sown in late spring, after the risk of frost is passed and things start heating up.
Additionally, for the cucurbits that need to spend the entire summer in a greenhouse, care should be taken to open the vents every day during blooming time, in order to let pollinators in: otherwise, they need to be pollinated by hand.
Cucurbits to grow:
Cucumbers
Cucumbers come in cultivars that are suited to both indoor and outdoor cultivation, as well as both mounding and vining forms: take care to read the seed package to see exactly how to cultivate the variety in hand. Exotic relatives of the cucumber, like the Kiwano -also known as the African horned cucumber - can be grown in a greenhouse all summer.
Gourds & Pumpkins
A favourite come autumn, gourds both decorative and edible come in an amazing array of forms and colours: warted, smooth, elongated, bottle-shaped, round, striped, tiny, enormous are just a few descriptors. For a useful addition to a garden of gourds, the “Luffa” or loofah gourd can be grown in a greenhouse, and the fruit dries to produce a natural abrasive sponge-like tool for the shower!
Melons
Muskmelons like the French heirloom "Charentais", or super-sweet watermelons like the "Sugar Baby" are easily cultivated from seedling stage to harvest in the warmth of a greenhouse.
Squash
Coming in green, gold, and orange colours; oblong, bottle, and "pattypan" shapes; and winter and summer harvest times, squashes are a multi-purpose crop.
Nightshades
These plants, belonging to the botanical family Solanaceae, are unexpected relatives: most gardeners don’t know that their tomatoes are related to both tobacco and petunias. They are generally heat-loving tropicals, most originating from South America.
Most of these plants benefit from "buzz pollination", which is something bumblebees provide. For those grown all summer in a greenhouse - barring the presence of bumblebees - they can be hand-pollinated with an electric toothbrush.
Nightshades to grow:
Aubergine
The large purple aubergines - or eggplants - seen in the supermarket aren’t the only option: this fruit also comes in white ("White Casper") and purple striped ("Antigua") colours, as well as round ("Aswad") and elongated ("Fond May") forms.
Physalis
Also called "ground cherries", these sweet little fruits grow packaged in their own little lantern-like casing, and are a decorative addition to summer salads. Started in a greenhouse in spring, most cultivars can happily be transplanted outdoors.
Pepino
Perhaps a little exotic, this nightshade tastes like a honeydew and a cucumber: the name means "sweet cucumber" in Spanish. This fruiting tropical will give the best results cultivated in a greenhouse all summer long.
Pepper
With sweet, mild, and super-hot options available, peppers can be cultivated all across the Scoville scale. Most are more productive spending the growing season in a greenhouse.
Potato
Though potatoes are an impractical crop to grow in a greenhouse, they can be "chitted" or sprouted there in late winter or early spring.
Tomato & Tomatillo
Both tomatoes and the smaller tomatillos vary between cultivars as to their cold-hardiness over summer. Some can be germinated in a greenhouse and then transplanted-out, whereas others should be cultivated inside a greenhouse all summer. Heirloom cultivars can give a huge range of colours, sizes, and patterns that are not typically available in a grocery store.
Tropical Annual Flowers
All the delightful annuals that can be found in flats in a garden centre can instead be started at home from seed, in a greenhouse. The options are too numerous to list, but browsing the seed selections for flowers at a local store is a good place to get started.
Frequently Asked Questions
What types of plants are best for beginners to grow in a UK greenhouse?
For beginners, we recommend starting with:
- Leafy greens like lettuce, spinach and chard - these are quick-growing and tolerate cooler temperatures
- Brassicas such as kale and cabbage - these germinate even in soil temperatures as low as 10°C
- Tomatoes - particularly cherry varieties which tend to be more forgiving
- Annual flowers - providing color while you gain experience
These plants offer relatively quick results and are more forgiving of temperature fluctuations, making them perfect for those just getting started with greenhouse gardening.
How do I manage temperature and ventilation in my greenhouse throughout the seasons?
Temperature management is crucial for successful greenhouse growing:
- Spring: Open vents on warm days but close before evening to retain heat. Consider shade cloth as days get warmer.
- Summer: Maximum ventilation is key - keep doors and vents open during hot days. Use shade cloth to prevent overheating.
- Autumn: Reduce ventilation gradually as temperatures drop. Clean glass to maximize light penetration.
- Winter: Minimize ventilation except on occasionally warm days. Consider bubble wrap insulation or heating for tender plants.
Install a min/max thermometer to monitor temperature fluctuations and adjust your ventilation strategy accordingly.
What's the optimal timing for starting different crops in my greenhouse?
For UK greenhouse growing, timing is everything:
- Late winter (Jan-Feb): Start slow-growing crops like leeks, onions, and some perennials
- Early spring (Mar-Apr): Sow brassicas, leafy greens, and begin chitting potatoes
- Late spring (May): Start heat-loving plants like tomatoes, cucumbers, peppers, and aubergines
- Summer (Jun-Aug): Begin autumn/winter crops like winter cabbage and sprouting broccoli
- Autumn (Sep-Oct): Sow winter lettuce, spring onions, and overwintering broad beans
These timings can be adjusted based on your specific location within the UK and local climate conditions.
How do I deal with pollination for greenhouse plants?
Pollination can be challenging in an enclosed greenhouse:
- Open vents and doors during flowering to encourage bees and other pollinators to enter
- For nightshades (tomatoes, peppers, aubergines), use an electric toothbrush against the flowers to simulate "buzz pollination"
- For cucurbits (cucumbers, melons, squash), hand-pollinate by transferring pollen from male to female flowers using a small brush
- Consider introducing bumblebees if you have a larger greenhouse
- Choose self-pollinating varieties when possible to reduce the need for manual pollination
Regular pollination checks will ensure you get the maximum yield from your greenhouse crops.
What exotic or unusual plants can I successfully grow in a UK greenhouse?
A greenhouse opens possibilities for growing plants that wouldn't normally thrive in the UK climate:
- Pepino - A sweet cucumber-flavored tropical fruit related to tomatoes
- Melons - Try varieties like the French Charentais or compact Sugar Baby watermelons
- Physalis (Ground Cherries) - Sweet fruits with decorative lantern-like casings
- Luffa Gourds - Grow your own natural sponges for the bathroom
- Exotic Aubergine Varieties - Try white 'Casper' or purple-striped 'Antigua' for something different
- Heirloom Tomatoes - Experiment with varieties in unusual colors and patterns not found in shops
With proper temperature control and care, these unusual plants can thrive in your greenhouse and provide unique additions to your garden and kitchen.