Germinating cucumber seeds indoors for outdoor transplanting typically takes seven to 10 days if correctly done. By soaking cucumber seeds in warm water, gardeners can germinate the seeds in one to three days. Although some seeds in a batch may germinate overnight, most of them will take a couple more days. This method is also useful for older seeds that may have a lower germination rate or for rare and expensive seed for which you want to ensure germination.
Basic Cucumber Requirements
Related to squash and melons, annual cucumbers (Cucumis sativus) grow in bush form or on vines 3 to 8 feet long and have specific growing requirements. They thrive in organically rich, loose fertile soil that drains well. Cucumbers evolved in the East Indies and need full sun; they grow best in hot summer weather with warm nights. Although nurseries sell cucumber seedlings, you can easily germinate cucumber seeds indoors.
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Cucumber Seed Sprouting Basics
Quick sprouting of cucumber seeds is not difficult. Placing cucumber seeds in warm water activates growth enzymes that causes them to grow tiny roots. That's when you transplant them in potting mix for growing seedlings, or you can transplant outdoors. They will later grow stems and leaves. This same quick method of germinating seeds is used to grow sprouts for salads and sandwiches.
How to Sprout Cucumber Seeds
Soak the seeds in water for five to 10 hours before draining them. Dampen a paper towel in warm water. Fold the seeds into the towel. To keep the moisture in the towel from evaporating, put it in a plastic bag or box. Keep the temperature of the towel above 70 degrees Fahrenheit. Check the seeds at least once daily. When you spot seeds that have developed roots, transplant them into a potting mix. If the roots have grown into the towel, tear the towel around the roots and plant both together to avoid damaging the delicate roots.
Plant the rooted seeds 1/2 inch deep in 3-inch-wide peat pots containing a potting soil mix of 1 part vermiculite, 1 part perlite, 2 parts of screened compost and 4 parts of sphagnum peat. To this add enough dolomitic lime to bring the mix to a pH of 6. Garden supply centers sell these ingredients and a kit to measure pH. The dolomitic lime comes in a powder. Wear a mask when handling it so you don't inhale it. You can also use commercial potting mix that's already blended for to promote seedling growth.
Standard Indoor Germination
Although soaking cucumber seeds allows them to germinate faster than sowing them directly in soil, standard indoor germination doesn't require watching for roots developing on individual seeds. Sow one to three cucumber seeds on their sides 1/2 inch deep in 3-inch-wide peat pots with the same mix you used for the pre-sprouted seeds that developed roots. Moisten the mix, cover it with a plastic bag so the moisture doesn't evaporate or water it when the mix becomes dry. Do not allow the mix to become soggy. Keep it between 70 and 85 F. Do not plant cucumber seedlings outdoors until soil temperature reaches 60 F. Space them 18 to 36 inches apart.