Cucumbers are seeded or transplanted outside in the ground no earlier than 2 weeks after the last frost date. Cucumbers are extremely susceptible to frost damage; the soil must be at least 65ºF for germination. Do not plant outside too soon!
For an early crop, start cucumber seeds indoors about 3 weeks before you transplant them in the ground. They like bottom heat of about 70ºF (21ºC). If you don’t have a heat mat, put the seeds flat on top of the refrigerator or perch a few on top of the water heater.
Before you plant outside, select a site with full sun.
Ideally, soil should be neutral or slightly alkaline with a pH of 7.0. Improve clay soil by adding organic matter. Improve dense, heavy soili by adding peat, compost or rotted manure. (Get a soil test if you are unsure of your soil type; contact your local county cooperative extension.) Light, sandy soils are preferred for northern gardens, as they warm quickly in the spring.
Mix in compost and/or aged manure before planting to a depth of 2 inches and work into the soil 6 to 8 inches deep. Make sure that soil is moist and well-drained, not soggy.
Sow seeds in rows, 1 inch deep and 6 to 10 inches apart.
If you are transplanting seedlings, plant them 12 inches apart.
A trellis might be a good idea if you want the vine to climb, or if you have limited space. Trellising also protects the fruit from damage from lying on the moist ground.
When planting seeds in the ground, cover with netting or a berry basket to keep pests from digging out the seeds.
When seedlings emerge, begin to water frequently, and increase to a gallon per week after fruit forms.
When seedlings reach 4 inches tall, thin plants so that they are 1½ feet apart.
If you've worked in organic matter into the soil before planting, you may only need to side-dress your plants with compost or well-rotted manure. Or, if you wish, use a fertilizer from your garden store which is low nitrogen/high poatassium and phosphorus formula and apply at planting, 1 week after bloom, and every 3 weeks with liquid food, applying directly to the soil around the plants. Or, you can work a granular fertilizer into the soil. Do not overfertilize or the fruits will get stunted.
Water consistently; put your finger in the soil and when it is dry past the first joint of your finger, it is time to water. Inconsistent watering leads to bitter-tasting fruit. Water slowly in the morning or early afternoon, avoding the leaves.
Mulch to hold in soil moisture.
If you have limited space or would prefer vertical vines, set up trellises early to avoid damage to seedlings and vines.
Spray vines with sugar water to attract bees and set more fruit.