Why Prune Cucumbers?
Cucumbers are rather like indeterminate tomatoes, given half a chance they’ll take over, filling the greenhouse with haulm (stems and leaves). What we actually want are the fruits and enough leaves to support their production, not monster masses of vegetation.
Just like a tomato, where the leaf joins the stem, the cucumber will start another stem. Left alone, this stem will form more stems and those in turn yet more stems. By pruning back to one or two leading stems, the plant’s energy will go into the fruits.
Prune Cucumber Sideshoots Early
Pruning cucumbers is essentially the same as pruning tomatoes. The sideshoots both come from the point where the leaf joins the stem. The earlier the sideshoots are removed the better and easier as energy is not wasted in producing foliage that will be removed.
Identifying Where to Prune Cucumbers
Unlike tomatoes, the joint where the the sideshoot grows from also produces a tendril and a fruit / flower. This should make it more obvious where the sideshoots are and so make pruning cucumbers easier but because of the speed cucumbers grow and the sheer size and volume of foliage it can be confusing. A case of not seeing the wood for the trees.
How to Remove Cucumber Sideshoots
Another difference to pruning tomatoes when pruning cucumbers is how the sideshoots are removed. With tomatoes the sideshoots are ripped or twisted off as, surprisingly, the scar heals better than a clean cut. The opposite is true of cucumbers.
When small, pinch the sideshoot off using your thumbnail to provide a cutting edge but for larger stems use a sharp pair of secateurs to achieve a clean cut as near to the joint as practicable.
The excellent video below from American seed supplier Johnny’s Seeds shows the process of pruning cucumbers very clearly.