When To Move Cucumbers Outside? (and how to harden them off)

When To Move Cucumbers Outside

Cucumbers grow vigorously through summer, & produce loads of juicy fruits–but you need to know exactly when to move cucumbers outside. They’re heat-loving vegetables that won’t do well if you move the seedlings out when the ground is still cold. Transplanting too late isn’t good, since it’ll shorten your growing season.

Cucumbers should be transplanted outside at least 2 weeks after the last frost date. Since they are extremely susceptible to frost and cold damage, make sure there’s no chance of frost once they’re in the ground and the soil temperature is at least 60ºF.

The exact timing depends on your climate, the number of growing days that the specific variety requires and how long has it been growing indoors. Other than the timing, you’ll also need to be careful about how to harden off the seedlings and transplant them into the garden to make sure they grow into productive plants. 

When To Move Cucumbers Outside

When To Move Cucumbers Outside

Cucumbers are warm-season crops that don’t tolerate frost or cold. 

Cucumber seeds won’t germinate in cold soil. 

Cucumber seed germination temperature ranges from 60ºF to 105ºF, but should ideally be at least 70ºF. 

The ideal germination temperature occurs somewhere between late May to June in the garden soil which is when you’ll be planting the seeds for direct seeding.

However, in areas with shorter growing seasons, direct seeding isn’t the most suitable option since it won’t give enough time to the vines to grow to full maturity before the temperatures start dropping again in fall.

Alternatively, gardeners, particularly those living in short-season climates, choose to start cucumber seeds indoors and move them to the ground once the temperatures are suitable. 

When growing cucumbers from transplants, wait at least 2 weeks after the last spring frost before transplanting the cucumber seedlings in the garden. The soil temperature in the planting bed must be 70ºF or higher at the time of transplanting the seedlings. 

Growing Cucumbers From Transplants

Seedlings should grow at least 3 to 4 weeks until they are strong enough to handle the transplant. 

For this reason, plan to sow the seeds indoors 2 to 3 weeks before the last frost date. 

Once the seedlings have had some time to develop indoors, they’ll be healthy enough to handle relocation.

Only transplant once the seedlings are big enough and the outside weather is suitable before moving the young plants into the garden bed.  

Check out the full answer for whether frost will kill cucumbers.

When To Transplant Cucumber Outside

When To Transplant Cucumber Outside

Like most other heat-loving vegetables, cucumber plants are very sensitive to cold. 

Cucumber seeds need the soil temperature to be at least 70ºF for viable germination.  

Other than the cucumber seeds, seedlings will also grow slower and weaker if they are planted in soil that’s too cool. 

Timing the planting season correctly is one of the most important things in ensuring a good harvest.

If you plant too early, the plants will grow slow, spindly and will not produce well. 

If planted too late, cucumbers won’t get the optimal number of days they need to come to harvest.

Depending on the variety, cucumbers take between 45 to 70 days to come to harvests when grown from seed and 35 to 60 days when grown from transplants

Plan the planting time such that cucumbers can receive their maximum number of growing days while the temperatures are within the optimal range. 

Plan The Planting Time

Whether you plant them through direct seeding in the ground or transplanting seedlings, cucumbers can go in the ground around early summer once the soil has warmed up to the ideal temperature. The ideal soil temperature for cucumbers occurs between May and June for most regions. 

To ensure that the seedlings are ready by the earliest transplanting time, you’ll need to give them around three to four weeks to develop indoors before they can be moved. 

Another consideration is not to let the seedlings get too big when growing indoors or they’ll become rootbound and experience problems as a result. 

Don’t start the seeds indoors any earlier than 4 weeks before the expected date of the last frost. 

Plants that have one or two true leaves transplant best so plan accordingly.

Protection From Unexpected Weather Changes

Protection From Unexpected Weather

If you fear a potential frost once you’ve set the cucumber seedlings in the garden, you can use a cold frame on the young plants to prevent any damage. 

Cold frame is simply an enclosure with a transparent roof, built low to the ground to protect young plants from cold and frost. 

How To Plant Cucumber Seedlings Outside

How To Plant Cucumber Seedlings Outside

Transplanting cucumber seedlings carefully to prevent transplant shock is just as important as the transplanting time. 

Cucumbers, just like other cucurbits, are very sensitive to disturbance

When transplanting cucumbers, you need to take extra care not to damage the long taproot or the plant won’t grow well and may even fall prey to different diseases. 

To make transplant easier and less risky, many gardeners plant cucumber seeds indoors in peat pots. 

Peat Pots

When the time is right to move the seedlings to the garden, they simply bury the peat pots in holes in the planting bed without the risk of causing any disturbance to the young roots. 

  • Preparing The Site

Choose a site with full sun. 

Prepare the planting bed for cucumber seedlings 2 weeks before transplanting them outdoors.

Break up the soil, remove stones and debris and incorporate plenty of compost into the top 8 inches of soil.  

  • Hardening Off Seedlings

Wait until the outdoor temperature is at least 60°F.

Place the seedlings outdoors for two to three hours at a shaded spot on the first day.

During the next ten days, increase the number of hours they spend outdoors and the exposure to sunlight.

If it’s forecasted that the temperature will drop below 60°F, bring the plants indoors for the day.  

  • Planting Cucumber Seedlings

Dig planting holes 12 inches apart from each other. 

The hole should be slightly bigger than the seedling’s original pot. 

If the seedlings are in peat pots, just place the pot into the hole and barely cover with soil so that the pot is at soil level. 

Pat the ground gently.

Once all the cucumber seedlings are in the ground, water them deeply or offer a drink of compost tea. 

Maintain consistent watering throughout the growing season, offering a drink each time the top ½ inch of soil dries out. 

After 4 weeks of transplanting, sidedress with compost to replenish the soil nutrients for healthy growth of the plants. 

You might also want to check out the articles on growing specific cucumber varieties:

When To Transplant Cucumber Seedlings Outside

When To Transplant Cucumber Seedlings Outside

So you know that cucumber seedlings are very specific about their planting times if you want to see them develop into thriving plants that bring bundles of harvests. 

There are several considerations to keep in mind when deciding the right time to plant the seedlings outdoors.

Here are some things to think about:

  • Number of growing days for the specific variety you are growing
  • Date of the last spring frost
  • Outdoor soil temperature
  • Age of the seedlings (don’t let them outgrow the peat pot)
  • Number of days you’ll have the optimal temperatures for cucumbers

Keeping a rough idea of all the considerations in mind, it’s easy to figure out when to plant cucumber seeds indoors and exactly when to relocate them outdoors into the planting bed. 

Experts recommend transplanting cucumber seedlings outdoors once the soil temperatures are expected to stay consistently above 60ºF. Cucumbers cannot tolerate frost so only transplant them outdoors once the soil has warmed up to the optimal temperatures and there’s no forecast of frost through the rest of the season. 

Best Time To Go Outside

Early summer is usually the best time for cucumber seedlings to go in the garden. 

In most areas, the ideal time to transplant is somewhere in the months of May and June. 

If you plan on growing cucumbers through direct seeding, you’ll plant the seeds in the ground around the same time. 

Most varieties will take 45 to 70 days to produce fruit from the day of planting the seeds so you can expect to start harvesting by mid to late summers, depending on the variety. 

You’ll probably want to check out the full article on how long it takes a cucumber to grow.

Conclusion

When To Move Cucumbers Outside? (And How To Harden Them Off)

Growing cucumbers isn’t hard at all if you can just get the planting and transplanting times right. 

Planted at the correct time, you can offer cucumber just the ideal weather conditions to grow and produce a healthy crop. 

With just a little bit of care, you can grow loads of homegrown cucumbers to eat right off the vine, add them to salads or turn them into pickles and enjoy for the rest of the year!

About the author

Greg Volente

Greg Volente holds a Naturalist Certificate from the Morton Arboretum, worked for The Nature Conservancy leading environmental education programs and doing natural areas restoration, and worked in the soil science research & testing lab at Michigan State University. Besides gardening, he's an avid wildflower enthusiast, and loves botanizing, hiking, and backpacking.

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