Sowing cucumbers: in pots or in open ground

Choosing the variety and sowing method

Check the seed packet to see if the variety is suitable for a greenhouse, outdoors, or both: the RHS distinguishes between these growing conditions. Keep this information on the label.

Pots require a warm location, then sufficient light to raise the seedlings. Direct sowing avoids transplanting, but the seed immediately depends on garden conditions. Choose based on your equipment and the weather, without trying to start as early as possible.

When to sow cucumbers?

The SNHF places sowing in pots in March–April in a heated greenhouse, followed by planting or outdoor sowing in May, when frosts are no longer a risk. Wait until the garden is warm enough before moving from protected sowing to planting.

Start from the period when you can plant out the seedlings, taking local forecasts into account. The University of Maryland warns that sowing too early can sometimes produce elongated seedlings with cramped roots. Also plan for their acclimatisation; the Ice Saints alone do not determine when to move them outside.

Sowing in pots and monitoring emergence

Use clean containers with drainage holes to allow water to escape, as advised by Maryland. Prepare seed-sowing compost and a dated label.

The RHS method provides the following guidelines:

1. Fill 10 cm pots and moisten the compost.
2. Sow one seed per pot, on its side, at 1–2 cm depth.
3. Maintain around 21 °C for germination.
4. Emergence is expected in one to two weeks, as a guide. Remove any cover as soon as seedlings appear, then keep them warm and in bright light.

Monitor moisture without waterlogging the substrate. The University of Maryland notes that excess water deprives roots of oxygen. Stems stretching towards a window may also indicate insufficient light: warmth alone is not enough. The sowing guide covers preparation and basic techniques.

Sowing directly in the garden

Wait until the risk of frost has passed and the soil is warmed. The University of Minnesota advises checking that the soil is at least about 21 °C at a depth of 2.5 cm before direct sowing. This is their practical benchmark, not a universal germination minimum or an air temperature.

Prepare loose, well-drained soil enriched with garden compost, in full sun. The SNHF recommends one metre in all directions between plants; adjust spacing based on the variety and whether it will be grown along the ground or on a support.

The RHS suggests sowing up to three seeds per spot, at 1–2 cm depth, then keeping only one plant. To thin, cut excess seedlings with scissors rather than pulling them out: the University of Maryland recommends this to avoid disturbing neighbouring roots.

Acclimatising before planting

For seedlings raised under cover, start by placing them outdoors during the day in a spot sheltered from wind and strong sun, then bring them back indoors at night. Gradually increase their exposure based on the weather. The RHS provides a general guideline of two to three weeks, which varies depending on growing conditions. This transition does not make cucumbers frost-resistant.

For planting, the RHS recommends waiting until temperatures stay above 12 °C, in greenhouses as well as outdoors. Pay particular attention to night-time temperatures: this planting threshold is different from the 21 °C sowing guideline. Even an unheated greenhouse must be monitored.

The University of Minnesota notes that a seedling planted in cold soil grows poorly and should not be left to outgrow its container. When transplanting, keep the root ball intact and handle gently, as advised by the University of Maryland. The cucumber growing guide continues with advice after planting.