Quick Answer: Greenhouse cucumbers want 75–80°F days, 60–70°F nights, and 80–90% relative humidity, per university extension guidance — a wetter target than tomatoes or peppers need. The bigger surprise is pollination: most modern greenhouse cucumber varieties are parthenocarpic, meaning they set seedless fruit without any pollen transfer at all, and letting bees in to “help” typically produces misshapen or bitter cucumbers instead of better ones. Pick a parthenocarpic hybrid, keep the structure sealed against pollinators, train the vines vertically, and almost any of our greenhouse kit picks will carry a productive cucumber crop.
Cucumbers round out our crop-guide series alongside greenhouse tomatoes and greenhouse peppers, but they break the pattern in the one place growers least expect: pollination. Tomatoes need a vibration to self-pollinate, peppers need physical agitation to release pollen from porous anthers — cucumbers, if you pick the right variety, need none of that, and inviting bees in can actively hurt your harvest.
Greenhouse cucumbers by the numbers:
- 75–80°F day, 60–70°F night — the university extension target range for greenhouse cucumbers until the first picking, with night temperatures allowed to drift no lower than 60°F for earliest production.
- 80–90% daytime RH — what Colorado State Extension says humidity-loving crops like greenhouse cucumbers need, the highest humidity target of any crop in our guide series, though sustained readings that high raise powdery mildew and botrytis risk without matching airflow.
- 6 inches — how tight vertical trellising can push in-row plant spacing, versus 12–24 inches for vines left to sprawl on the ground, roughly doubling plants per square foot of greenhouse floor.
- 2 plants per square foot — a commonly cited planting density for vertically trellised cucumbers, made possible by training vines up rather than letting them spread horizontally.
How cucumbers compare to tomatoes and peppers
If you’ve already read our other crop guides, the temperature numbers will look familiar — the pollination story won’t:
| Factor | Tomatoes | Peppers | Cucumbers |
|---|---|---|---|
| Day temperature | 75–80°F | 70–80°F | 75–80°F |
| Night temperature | 60–65°F | 60–70°F | 60–70°F |
| Humidity target | Disease-pressure concern | 65–85% (fruit-set-critical) | 80–90% (highest of the three) |
| Pollination | Self-fertile, needs vibration | Needs physical agitation | Often none needed — parthenocarpic hybrids set fruit unpollinated |
| Bees in the structure | Not required, harmless if present | Helpful if present | Can actively cause deformed or bitter fruit |
| Growth habit | Indeterminate, needs tall trellis or lower-and-lean | Bushy, little to no trellis | Vining, wants a vertical trellis but stays shorter than tomato vines |
That pollination row is the one that trips people up. It’s tempting to assume more pollinators are always better in a greenhouse — cucumbers are the crop in this series where that assumption backfires.
Picking a variety that matches how you’re growing
The variety decision matters more for cucumbers than for tomatoes or peppers, because it determines whether pollination helps or hurts you:
- Parthenocarpic hybrids (Diva, Sweet Success, Tasty Jade, and similar greenhouse-bred varieties) set fruit without pollination. Grown in a sealed structure with no bee access, they produce smooth, seedless, often burpless fruit — but if a bee does get in and pollinate a flower, the resulting cucumber typically comes out misshapen, oversized in the seed cavity, or bitter.
- Standard open-pollinated varieties need bees or hand-pollination to set fruit at all, the same as an outdoor cucumber patch, and are a poor fit for a bee-excluded greenhouse.
Because of the cross-pollination risk, most greenhouse growers don’t mix the two types in one structure — they pick parthenocarpic varieties specifically to grow indoors and keep the greenhouse sealed against pollinators, rather than trying to manage pollination at all.
QueenBird Heavy-Duty Trellis Netting
- Strings across an overhead or A-frame support so cucumber vines climb vertically instead of sprawling across the floor, freeing up growing space for other crops.
- Tightens usable in-row spacing to as little as 6 inches between plants versus 12–24 inches for ground-trained vines.
- UV-treated nylon holds up to a full season of vine weight and can be rolled up and reused the next year.
Vertical growing means more small hardware — netting clips, twine, an extra length of trellis — showing up on your doorstep throughout the season, so try Amazon Prime free for 30 days if you’d rather have those arrive in two days than wait on standard shipping mid-grow. Sponsored link — we may earn a fee if you sign up. No extra cost to you.
Hitting the temperature window
Keep daytime temperatures at 75–80°F and nights around 70°F until the first fruit is picked — night temps shouldn’t drop below 60°F if you’re after the earliest possible harvest. Once picking starts, you can gradually reduce night temperatures by about 2°F per night down to roughly 63°F, which helps moderate vine growth without shocking the plant. Soil temperature matters too: extension guidance targets 70–75°F during the day and at least 65°F at night, since cold roots slow fruiting even when the air temperature looks fine.
A greenhouse heater covers the cold-night side of that window, and because cucumbers want the highest humidity of any crop in this series, pairing it with a greenhouse humidifier matters more here than it does for tomatoes or peppers. Ventilation is the other half of that equation — our ventilation guide covers sizing a fan or vent opener so 80–90% humidity doesn’t turn into a fungal disease problem.
Training vines vertically
Left on the ground, a cucumber vine sprawls several feet in every direction and is spaced 12–24 inches apart in the row with 3–4 feet between rows to give it room. A vertical trellis — string, netting, or wire — changes that math: training vines upward lets you tighten spacing to as little as 6 inches between plants, which is how growers get to roughly two plants per square foot of greenhouse floor instead of one sprawling plant eating several square feet. Vertical growing also improves airflow around the leaves, which helps manage that 80–90% humidity target without inviting as much fungal disease as a dense, ground-sprawling canopy would.
How to choose
- Pick a parthenocarpic variety if you’re growing indoors. It’s the single decision that determines whether keeping bees out helps or hurts your harvest.
- Seal the structure against pollinators, don’t invite them in. This is the one crop guide in our series where more pollination access is a liability, not a bonus.
- Budget for the highest humidity target of the three crop guides. 80–90% RH is wetter than tomatoes or peppers want, so pair a humidifier with real airflow, not just a sealed structure.
- Train vertically from the start. Retrofitting a trellis around an already-sprawling vine is harder than stringing netting before you transplant.
- Watch for the same pests as tomatoes and peppers. Aphids and whiteflies target cucumber foliage just as readily — our greenhouse pest control picks cover early intervention.
The bottom line
Cucumbers share the same rough temperature window as greenhouse tomatoes and peppers — 75–80°F days, 60–70°F nights — but flip the pollination script entirely: pick a parthenocarpic variety, keep the structure sealed against bees, and train vines vertically, and a compact walk-in greenhouse will out-produce a bigger structure where pollination access or trellising was an afterthought.
Still shopping for the structure itself? Our best greenhouse kit roundup and best small greenhouse picks cover the walk-in options this guide assumes you’re growing in.