When to plant cucumber seeds – for a bumper harvest

It’s important to know when to plant cucumber seeds to maximize your chances of success.

Learning how to grow cucumbers is an achievable goal for even the most inexperienced gardener, as the plants are relatively trouble free. They are also an attractive crop, with their creeping vines and bright yellow flowers.

Plus, if you know how to grow cucumbers vertically, they can be highly space-efficient, which makes them an essential addition to your kitchen garden ideas.

However, you if plant the seed at the wrong time, you risk seedling failure, a poor quality harvest, or the seeds may not germinate at all.

When to plant cucumber seeds indoors

As with knowing when to plant vegetables in general, when you plant cucumber seeds will depend on whether they will be planted indoors or outside.

For the best chance of germination, you should plant cucumber seeds indoors – either positioned next to a sunny window, or in a greenhouse.

‘Expensive seeds such as cucumbers are best sown indoors because germination is far more successful in a protected environment,’ says growing expert Lucy Chamberlain.

Cucumber seeds can take a couple of weeks to germinate, so you can start them off a little earlier than many salad crops. 

This is usually March or April, but can be as early as February in a heated greenhouse.

‘As cucumbers need plenty of time in the sun to ripen, sow the seeds in early spring to ensure that you have good-size plants – say, 4 inches (10cm) or so in height – by the time the frosts are over and they can go outside,’ says Aaron Bertelsen author of Grow Fruit and Vegetables in Pots.

To minimize the chance of seed rot, it’s a good idea to position them at the outer edge of the pot, and lay them on their side. They should be planted about half an inch deep. Keep the soil moist, but not over wet.

Before planting out your cucumber seedlings, it’s best to harden them off in a sheltered area for a couple of days, so they will cope with the change of weather.

‘Cucumbers will need daily watering once the fruits start to develop – after all, they are 96 per cent water – and a dose of liquid feed every ten days or so,’ says Bertelsen.

Make sure you know how to prune cucumber plants to maximize fruit production as they grow.

When to plant cucumber seeds outdoors

If you wish to plant your cucumber seeds directly outdoors, then you will need to start them off later than if grown indoors.

Sow the seeds between late spring and early summer – roughly May to June, depending on your local climate.

Position them in a sunny spot that's sheltered from strong winds, and plant them in single rows around 35 inches apart.

If you wish to train the plants onto trellis or canes, it's best to insert these now. There are many wonderful vegetable garden trellis ideas to explore.

Alternatively, allow the cucumber vines to sprawl across the ground as they grow.

It's a good idea to look at options for cucumber companion planting, to deter pests and improve flavor.

When is the best time to plant cucumber seeds?

Spring is the best time to plant cucumber seeds, but there is flexibility within this time period, and you might want to try succession planting to ensure a steady summer supply.

‘I get them going under cover in March or April, potting them on as needed before planting them out in May (after hardening them off for a couple of days),’ says Mark Diacono, expert grower and author of River Cottage Handbook: Veg Patch.

‘If you sow in April you can expect a good harvest from August onwards, although you can always try a March and May sowing too if you are particularly keen to maximize your chances of a long and heavy haul.'

Is it too late to plant cucumbers?

Depending on your local climate, June or July is the latest possible date you can plant cucumbers in order for them to be able to yield any fruit.

When planted in warmer weather, the plants will establish much more quickly than when planted in the spring.

August will likely be too late to plant cucumber seeds, though you may be still able to find young plants at the garden center that you can grow on at home.

How long does it take to grow cucumbers from seed?

Cucumber seeds take up to two weeks to germinate, and around 12 weeks to produce fruit.

Harvest your cucumbers when they are young and tender for the best flavor.