When spring arrives the biggest factor for getting a good start to the growing season is the temperature of the ground.
Soil temperature is a factor few plot holders check before planting, yet it is probably the most important factor affecting seed germination.
As spring progresses the Sun rises higher in the sky and the ground is exposed to more direct sunlight, and so the plot warms up.
This is offset by the night temperatures when any heat gained during the day is released to the colder night air.
Anything that can improve the rate of heating and conserve it will improve the date at which planting will be most effective i.e. the seeds germinate quickly rather than sit in cold damp soil waiting for the germination temperature to be reached.
Covering the soil with black materials increases the temperature of the soil.
Black materials are black because nearly all of the light hitting the material is absorbed by it.
White materials are the opposite, nearly 100% of the light bounces off it, red materials are red because they absorbs all the other colours but reflect red light.
When the light is absorbed by the material it heats up, and this is transferred to the air above the soil and the soil itself. The material covering also acts like a blanket and keeps the warmth in during the night when the temperature drops.
Common materials for covering plots are black plastic and weed control fabric.
Black Plastic Sheeting
Black Plastic is very often used by farmers to cover bales of hay for conversion to silage over the Winter, the increase in temperature accelerates the growth of the micro-organisms in the bale that convert hay to silage. Sheets of black plastic are ideal for plots where waterlogging can be a problem as they do not let water through, keeping the soil dry. Black Plastic sheeting is manufactured in a number of thicknesses for different purposes. For plot protection choose a heavy duty sheeting that is at least 125microns or 500gauge thick. Thin sheeting will tear easily if you use staples or pegs to hold it down to the soil.
Weed Control Fabric
This is a woven material made from tough manmade fibres that has the same light absorbing properties but will allow water through to the soil. If your plot is in a sandy /dry soil area this may be the best option.
Dig a small trench along both edges of the plot, retain the soil. Put the edge of the sheeting into the trench and backfill with the retained soil.
Plastic pegs are about 6” in length with barbs along its length to retain it in the soil. Lay the sheeting over the plot and fix with pegs every metre or so along at least two sides. If the plot is exposed consider fixing on all four sides.
A larger versions of the paperwork staple. These can be used in the same way as plastic pegs. Weed Control Fabric
You can always weigh the sheeting down with bricks, rocks or boards. Ensure you cover all the sides as wind can get under the sheeting easily and add it to your neighbours plot!
Both types of material can be used to cover the plot over the winter period and into spring then removed during the active growing season.
Alternatively you can leave the sheeting down once the soil warms up and then cut holes in the sheeting and plant through it into the soil.
This has advantages in that the sheeting acts as a mulch keeping water in and weeds down and providing more warmth to the soil. Once the growing season has finished remove the sheeting carefully, turn over the soil, fertilise, rake to a fine tilth ready for planting and return the sheeting for the winter.
All of these items can be found in our Fabrics & Membranes section