When to plant cucumbers?

Updated 4 November 2026 · By the Orto editorial team

Sow cucumbers indoors at 21 °C: from mid-February to mid-March in a heated greenhouse, in April in an unheated one, and in late April for outdoor plants. In the open ground they go out once the air stays above 12 °C, from early June in the north, and Campania sets no month: it asks for nights at 18-20 °C and days at 24-28 °C.

Young cucumber plants just transplanted at the base of a trellis net

When, by region

	North	Centre	South
Sow indoors	Heated greenhouse from mid-February to mid-March, at 21 °C. Unheated greenhouse in April. For outdoor plants, late April. One seed, 1-2 cm deep, in a 10 cm pot.	Umbria's guide does not fix a month. The same thresholds: 21 °C indoors.	No written month. In a greenhouse Sicily asks for days at 24-28 °C and nights at 18-20 °C. Without that heat, wait.
Open ground	From early June, once the air stays above 12 °C. Direct sowing in late May or early June. The soil, for University of Minnesota Extension, at least 21 °C at 2.5 cm.	The same 12 °C threshold. In Umbria, at least 3 years between crops, and no other cucurbits or solanums before.	In Campania the cover comes off once nights settle at 14-15 °C and days at 22-24 °C. Single rows, 1.5-3 plants per square metre. In Sicily, in a greenhouse, no more than 2.5.

The northern month is from the RHS. Centre and south follow temperature: the regional guides do not write a month.

Mid-February to mid-March in a heated greenhouse, April in an unheated one, late April for outdoor plants, 21 °C, planting out from early June above 12 °C, and direct sowing in late May or early June, are from the RHS. Soil at 21 °C (70 °F) at 2.5 cm (1 in), and seed about 13 mm (½ in) deep, are from University of Minnesota Extension. Nights at 18-20 °C and days at 24-28 °C, covers off at 14-15 °C at night and 22-24 °C by day, and 1.5-3 plants per square metre, are from Campania. The same 24-28 °C and 18-20 °C, and a greenhouse maximum of 2.5 plants per square metre, are from Sicily. The 3 years in the open ground, with no cucurbits or solanums before, are from Umbria. Courgettes, in the same family, have a different threshold: when to plant courgettes. The months are in the February calendar, April, May and June.

A short seedbed

The seed wants heat. The RHS sows it at 21 °C (70 °F), on its side, 1-2 cm (½–¾ in) deep, one to a 10 cm (4 in) pot. It shows in a week or two. University of Minnesota Extension does not start it indoors more than four weeks before the last frost, in a pot you plant whole, because the root resents the move. Those pots are in the homemade seedbed.

In a heated greenhouse you can plant from late March, if it stays above 12 °C (53 °F) inside. In an unheated greenhouse, from late May, at the same threshold. Outdoors, from early June. Two weeks of hardening off come first, as with the other heat-loving plants. The method is in starting seeds indoors.

Spacing, supports, pots

The RHS leaves 30 cm (1 ft) between plants, in the ground or in a pot at least 30 cm wide and deep. A growing bag takes two. Put the support in at planting: in a greenhouse a cane or a string to the roof, outdoors a wigwam or netting. Outdoors, once the plant has seven leaves, pinch the tip so side-shoots grow.

In Campania, at 20-25 °C, a fresh cucumber finishes its cycle in 80-100 days, and picking starts 40-60 days after planting, for 2-3 months. In a greenhouse the RHS keeps 18-25 °C (64-77 °F). Flowers on greenhouse varieties, almost all female, must not be pollinated, or the fruit is bitter: male flowers, with no tiny fruit behind them, come off. Outdoors you need the male flowers, because fruit sets only if the flower is pollinated.

In a pot the compost dries out on a hot day: see the container garden.

Water, and where not to return

Water the soil, not the leaves. The RHS says so for powdery mildew, and University of Minnesota Extension asks for about 25 mm (1 in) a week, on a drip line. In Umbria the thirst matters most at flowering and while the fruit swells. How much is in watering. A layer of compost or well-rotted manure, with a gap around the stem, is mulching.

The white dust is powdery mildew, the same one as on courgettes, under pests and diseases. In Umbria, in the open ground, wait at least 3 years, and do not put cucumber after cucumber, courgette, squash, melon, watermelon, tomato, pepper or aubergine. Under cover, after a run of crops, the gap is 2 years, for the other cucurbits too. The plan is in crop rotation.

In the app

Every plant in the catalogue has its own sowing calendar, and weather alerts for your area help you judge whether to sow now or hold off.

Frequently asked questions

Can I sow cucumbers in January?

No. In a heated greenhouse the RHS starts in mid-February, at 21 °C. In an unheated greenhouse, April. For outdoor plants, late April. January is too early even on a windowsill.

When do I plant them out in the north?

From early June, if the air stays above 12 °C. Direct sowing is late May or early June, with the soil at least 21 °C at 2.5 cm. Below that, the seed does not start and a plant set outside does not grow.

What month is it in the south?

Campania and Sicily do not write a month. In Campania the tunnel comes off once nights are at 14-15 °C and days at 22-24 °C, and the crop wants nights at 18-20 °C and days at 24-28 °C. In a Sicilian greenhouse, the same temperatures apply.

What pot, and which flowers do I remove?

A pot at least 30 cm wide, one plant, or two in a growing bag. In a greenhouse, remove the male flowers on all-female varieties, or the fruit is bitter. Outdoors, leave the male flowers.

Can I plant them where courgettes were?

Not in Umbria. In the open ground, at least 3 years, and no other cucurbits or solanums in between. Under cover, after repeated crops, a 2-year gap.