Question: We are anxious to get started on planting our garden but our soils are still very wet and cold. Is there anything we can do to help warm them up and dry them out?
Answer: Unfortunately, wet clay soils are notorious for staying cold late into the Spring in our coastal area. A simple way to expedite warming the soil is to simply cover the bare ground with clear polyethylene plastic film. Researchers at the Penn State Center for Plasticulture found that daytime soil temperatures under clear plastic mulch are generally 8 to 14 degrees F. higher at a 2 inch depth and 6 to 9 degrees F. higher at a 4 inch depth compared to those of bare soil. It is important when using plastic mulch that there be good contact between the soil and the plastic. If an air space is created between the plastic mulch and the soil by a rough soil surface, soil warming can be less effective than would be expected.
Black plastic mulches are not as effective in warming the soil. Much of the solar energy absorbed by black plastic mulch is lost to the atmosphere through radiation and forced convection. Soil temperatures under black plastic mulch during the daytime are generally 5 degrees F. higher at a 2 inch depth and 3 degrees higher at a 4 inch depth compared to those of bare soil.
Another family of mulches includes the wave-length selective or photoselective mulches, which selectively transmit radiation in some regions of the electromagnetic spectrum but not in the photosynthetic region. These mulches warm up the soil like clear mulch, but without the accompanying weed problems.
Building raised beds 10 to 12 inches above the normal soil level have many advantages for short season vegetable production. Soil in raised beds dries out and warms faster in the spring, and drainage is better throughout the season, allowing for earlier planting and better plant growth. Soils in raised beds with a southern exposure will warm more than level soil. Add new soil, or amend native soil during the formation of the beds. Make beds 3 to 4 feet wide so you can work from the pathways on either side, eliminating compaction from foot traffic.
Question: Are there any vegetables we can safely plant now?
Answer: Cool season vegetable seeds can germinate in soil that is 40 degrees F. or cooler. They are also able to grow and mature when exposed to cooler day and night temperatures. Most can resist some frost and light freezes. Vegetables that will germinate at 40 degrees F. include Fava beans, beets, broccoli, Brussels sprouts, Chinese cabbage, cabbage, carrots cauliflower, kale collards, kohlrabi, leeks, parsley, peas, radish, and rutabaga. Lettuce, onion, parsnip and spinach will germinate at 35 degrees F.
Choose early cultivars with the shortest days from planting to maturity. Even a few days can mean the difference between a harvestable crop or no crop at all.
Question: These past few weeks of sunshine and no rain have me dying to get out and begin working the soil for our vegetable garden. How can you tell when the soil is dry enough to work?
Answer: Here's an easy test to tell if the soil is dry enough to spade or rototill. Take a handful of soil and squeeze it into a ball in your fist. Then open up your hand and tap the soil ball. If it stays like a mudball and won't break apart it's not ready to work. Wait until later and try this test again. When the soil is ready to till the soil ball will fall apart in your hand when you tap it.
When the soil is dry enough to till begin with a general clean-up of the garden plot. Pull and remove plants that you suspect may be harboring insects or plant diseases. Also remove large weeds or plants you don't want in the garden. If organic matter or compost is available, spread it on the top of the soil. Then when you spade or rototill mix it in. You can add sawdust, peatmoss, wood ashes or aged cow manure that has been composted for one year.