Cucumbers are in the family of cucurbits, which also includes squash, pumpkins, & melons. They have similar cultural requirements and pests. Cucurbits do not do well in soil temperatures below 55F.
In some seasons, and with early plantings, a spell of four to five days of rainy or cloudy weather can cause losses. Without sunshine, the soil temperature drops below 55F, so that the transplant’s roots can no longer absorb water from the soil. When the sun reappears, the leaves transpire (release water vapor) releasing moisture much more rapidly than the roots can absorb water. The baby cucurbit suddenly wilts and dies.
There is no cure, but here are some management tips to try to prevent this problem.
- Hold off planting cucurbits until the weather is warm and settled and the soil has warmed. (Now should be fine.)
- If you want to plant early, choose a site that has a warmer micro-climate. Example, a southern facing slope rather than a northern one.
- Plant through black plastic, which you lay down on top of the planting bed once you’ve fertilized and moistened the soil. If you have only a hill or two of cucumbers, you can cut apart a black plastic bag. Take care to make sure the plastic is weighted down so the wind can’t pull it up or shift it, damaging your transplants. Sometimes we put rocks near the planting hole as well as weighing down the outer edges of the plastic or burying them in soil. The black plastic harnesses some solar heat and blocks out weeds.
- Gallon plastic jugs with the bottoms cut off and the caps removed will also help hold in the warmth around individual plants.
Other advice: seal a floating row cover over your young cucurbits, which not only increases the temperature a couple of degrees, it excludes insects such as flea beetles and cucumber beetles.
When you notice flowers on your cucurbits, you must remove the row cover to allow insect pollination, unless you plant parthenocarpic varieties.
Cucumbers that do not require pollination to produce fruit are called parthenocarpic. Some newer cucumber varieties are gynoecious, meaning they have only female flowers (the ones that make the fruit.) Gynoecious plants have earlier and higher yields.***
In a regular cucumber plant, such as Marketmore (which is open-pollinated, meaning you can save the seed and it will come true), the first 10-20 flowers are male, and for every female flower, 10-20 male flowers are produced.
Two of the varieties we grow, Diva and Cucino, are both gynoecious and parthenocarpic, meaning they have only female (fruit-creating) flowers which do not require pollination. Tasty Jade and Little Leaf Pickling are parthenocarpic, meaning you can exclude the pollinators (or even grow them indoors if you have a sunny enough room or use fluorescent lights) and you will still get cucumbers.
Our cucurbits are all started in peat pots, which practically eliminates transplant shock. Plant them deep, leaving the first set of leaves (the cotyledon or baby seedling leaves) about ½ to 1” above the soil surface. Do not remove the peat pot. The roots will grow right through the pot, and additional roots will also form on the stem below the cotyledon leaves where you have buried it in the soil. Fill the soil in around the plant gently, rather than pressing hard—most plants grow better when the soil is not compacted.
**New England Vegetable Management Guide, 2014-2015 Edition, pp. 159-160
*** Johnny’s Selected Seeds “De-Mystifying Cucumber Types and Terminology”, pdf 10/09