Can I grow tomatoes and cucumbers in the same greenhouse?
The old advice says never. The real answer is that they want different humidity and shading, and there are three practical ways to keep both happy in one house.
- Difficulty
- beginner
- Time
- 10 min
- Read
- 3 min
Short answer
Yes, and most people do. They are not incompatible, they just prefer different conditions — cucumbers want humid and shaded, tomatoes want drier and brighter. Put cucumbers at the shaded, sheltered end away from the door and tomatoes at the bright end, and manage the middle as a compromise.
The traditional rule that tomatoes and cucumbers must never share a greenhouse is an overstatement of a real difference. In commercial glasshouses they are separated because each crop is run at its own optimum. In a domestic greenhouse the choice is between a slight compromise for both and having only one crop.
Step by step
- Understand the actual conflict.Cucumbers want higher humidity, more warmth and shelter from direct sun. Tomatoes want good air movement, lower humidity to reduce botrytis, and all the light they can get. Neither preference is absolute — both grow acceptably in the other's conditions.
- Separate them by position within the house.Cucumbers at the end furthest from the door, where it is stillest and most humid, ideally on the shadier side. Tomatoes nearest the door and on the brightest side. Even in a 6ft by 8ft house that separation makes a real difference.
- Partition if you can.A curtain of polythene or bubble insulation across the house creates two microclimates. It is the same technique used for a heated zone and works just as well for a humid zone.
- Shade selectively.Shade the cucumber end and the roof above it more heavily, and leave the tomato end brighter. External netting fixed over part of the roof does this easily.
- Damp down at the cucumber end.Wetting the floor at one end raises humidity locally. Combined with the door being at the other end, the gradient across the house is bigger than you would expect.
- Water and feed each crop on its own schedule.Cucumbers need more water more often; tomatoes want thorough but even watering. Both use a high-potash feed once fruiting. Do not treat them as one crop with one watering can routine.
- Accept the compromise, or split by season.If you find both crops mediocre, grow cucumbers in the greenhouse and tomatoes outside against a warm wall, which works well in southern Britain, or grow one crop each year.
Tips
- Peppers, chillies and aubergines sit between the two and are happy in either zone, which makes them useful buffer plants for the middle of the house.
- Ventilation is the shared requirement. Whatever the humidity preference, still air is bad for both — cucumbers want humid moving air, not humid still air.
- Growing outdoor ridge cucumbers instead removes the conflict entirely and frees the greenhouse for tomatoes.
Common mistakes
- Treating the old rule as absolute and giving up on one crop — Both crops are perfectly achievable in one domestic greenhouse with sensible positioning. The rule comes from commercial practice where each crop gets its own house.
- Running the house humid for the cucumbers — That is what gives you botrytis on the tomato stems and fruit. Damp down locally, ventilate throughout, and let the gradient do the work.
- Planting them adjacent in the same border — Different watering needs in the same root zone means one of them is always wrong. Separate them along the length of the house.
Questions people ask
Why are you told not to grow them together?
Because their optimum humidity, temperature and shading differ, and commercial growers run each crop at its own optimum. In a domestic greenhouse the compromise costs you a little of each crop, which most people accept happily.
What else can share a greenhouse with tomatoes?
Peppers, chillies, aubergines and basil all want essentially tomato conditions and are the easiest companions. Melons want cucumber conditions.