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Cucumber Sowing and Growing Guide

Published: 27th April 2023

Cucumber Growing Guide


Cucumbers, benefit from warmer temperatures so unless you have a heated greenhouse it is better to delay sowing until late April or early May. Successional sowings can be made until the end of June for cropping until the end of September.

Sowings made in late April for planting in an unheated greenhouse in late May will produce a good crop of fruit through the end of August for one of the indeterminate types. Bush types such as ‘Bush Champion’ can be sown in early May for planting outdoors in pots or the vegetable plot in early June. Be aware if you do not have a greenhouse or conservatory, cucumbers are not likely to survive fully outdoors.


A kitchen windowsill or a heated propagator is perfect for germination. You can use either a seed tray (with or without grids), or a few small pots – filled with a seedling specific compost. Make sure you moisten the compost before planting your seeds. Plant your seeds evenly apart from each other with at least 1cm between each seed and sprinkle with a dusting of compost on top. Cover the seeds with a plastic bag if they are on a windowsill – this will keep the conditions warm and moist. If your seeds are in a heated propagator this won’t be necessary.

Cucumbers need to be kept very warm in the germination period. A temperature between 20-22 degrees Celsius is optimum.


Prepare to transplant your seedlings after about 10-12 days. Your seedlings should have one leaf on them before you consider moving over to pots. 9cm pots are perfect for cucumber seedlings, and they can stay in these for up to 4 weeks. Your cucumbers will still not withstand being outside at this point and will need to be kept inside on either a windowsill, in a conservatory or moved into a greenhouse/cold frame. Plants should not be moved outside into a non-heated greenhouse/cold frame before the mid-end of April. Cucumbers have no frost tolerance and will not survive in a non-heated greenhouse or a cold frame if there were a cold snap.


Indeterminate cucumbers must be planted in a greenhouse or conservatory in the UK climate to ensure strong growth and fruit development. Plants can be moved from 9cm pots into the soil, grow bags or a large pot (15 Litres in volume as minimum).  Plants should be supported on a bamboo cane and trained vertically or on a string attached to a horizontal wire running the length of the greenhouse. In all-female varieties like ‘Merlin’ or ‘Party Time’, fruit will start forming around 6-7 weeks from sowing in suitably warm conditions.


Harvest fruits when they are fully cylindrical and dark green. Break the fruits off with a thumb nail or use kitchen scissors to make a neat cut at the upper end of the fruit.

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