Step 5 - Greenhouses
What to Grow in a Greenhouse
A greenhouse is expensive floor space. The point is to use it for crops that genuinely cannot do as well outside.
Janet H. - the hands-on owner behind Janet Media Group.
Published - last updated
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Use greenhouse space for heat-loving crops that struggle outside in your climate, and for raising seedlings in late winter when nothing else can. Do not fill it with things that grow perfectly well in the open garden -- that is the most common way a greenhouse fails to pay for itself.
The year, month by month
| Season | Main job | Crops |
|---|---|---|
| Late winter | Seed starting, with a grow light | Tomatoes, peppers, eggplants, brassicas, onions from seed |
| Early spring | Hardening off and early sowings | Salad crops, radishes, early carrots in containers |
| Late spring | Plant the summer crop | Tomatoes, cucumbers, peppers, basil, chillies |
| Summer | Grow on, shade, ventilate hard | The above, cropping continuously |
| Autumn | Clear and replant for winter | Winter lettuce, spinach, mache, chard, herbs |
| Winter | Harvest hardy greens; little growth | Whatever was established in autumn |
The crops that justify the space
- Tomatoes. Earlier, longer-cropping and far less troubled by blight under cover than outdoors in a wet climate.
- Cucumbers. Greenhouse varieties are more productive and need the warmth and shelter.
- Peppers and chillies. In many climates these only ripen properly under cover.
- Basil. Hates cold nights and wet leaves; thrives in a greenhouse.
- Early salad crops. Weeks ahead of the open garden, at the time of year when salad is expensive.
- Seedlings of everything. The highest-value use of the space in February and March.
Not worth the space
Anything that grows perfectly well outside and takes up a lot of room: sweetcorn, squash, potatoes, brassicas grown to maturity, and most root crops. Grow those in the raised bed and keep the greenhouse for crops that need it.
The exception is raising their seedlings, which is a few weeks of tray space rather than a season of floor space.
Watering and humidity
Nothing under cover gets rain. Greenhouse crops depend entirely on you, and in summer a mature tomato plant in a container can need water daily.
Water the soil rather than the leaves, and water in the morning rather than the evening so foliage dries before nightfall -- wet leaves overnight in a humid structure is how fungal problems start. Damping down the floor on hot days raises humidity, which helps crops cope with heat and discourages red spider mite.
Pollination
Closed greenhouses exclude pollinators. Tomatoes and peppers are largely self-fertile and respond to a gentle tap on the flower truss or a fan. Cucumbers and squash are not -- either buy parthenocarpic greenhouse varieties that set fruit without pollination, or open the doors and vents while they flower.
For starting the seedlings that go in, see when to start seeds indoors. For running the structure day to day, greenhouse gardening tips.
What to buy
The products that fit the advice above, chosen by the process on our how we choose page. We have not hands-on tested them; specifications are the manufacturers’ own.
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Top pickPalram Canopia Mythos GreenhouseAluminum frame, 4 mm twin-wall polycarbonate | A first real greenhouse | 9.0 | Check price on Amazon |
| 2 |  Barrina T5 Full-Spectrum LED Grow LightsLinkable LED strips, full spectrum | Stopping leggy seedlings | 9.0 | Check price on Amazon |
| 3 |  VIVOSUN Seedling Heat MatWaterproof mat sized for 1020 trays | Peppers, tomatoes and slow germinators | 8.8 | Check price on Amazon |
| 4 |  Greenhouse Staging and Shelving UnitTiered staging sized for standard trays | Doubling usable space | 8.2 | Check price on Amazon |
#ad We may earn a commission - prices are shown by Amazon, not by us
Scores are our own editorial judgment, formed from published specifications and independent sources. They are not aggregated customer ratings, and they are not the result of hands-on testing, which we do not currently do. See how we choose.
Common questions
What is the best thing to grow in a greenhouse?
Heat-loving crops that struggle outside in your climate -- tomatoes, cucumbers, peppers, chillies and basil -- plus seedlings in late winter. Avoid filling it with crops that do perfectly well outdoors, which is the main reason greenhouses fail to earn their space.
Can you grow tomatoes in a greenhouse all year?
No, not without heat and supplementary light. Tomatoes need warmth and long days; in midwinter both are absent even inside a greenhouse. The realistic season runs from a late-spring planting through to the first cold nights of autumn.
Do greenhouse plants need pollinating by hand?
Tomatoes and peppers are largely self-fertile and respond to a tap on the flower truss or air movement from a fan. Cucumbers and squash need either pollinators -- open the doors while they flower -- or parthenocarpic varieties that set fruit without pollination.
How often should I water greenhouse plants?
Far more often than outdoors, because nothing under cover gets rain. In summer a mature tomato in a container can need water daily. Water the soil rather than the leaves, and water in the morning so foliage dries before night.
Sources
Factual claims on this page are backed by the published sources below, and product specifications are the manufacturers’ own. Where a figure is not published, we say so rather than estimating it.