Fungi, bacteria, and nematodes! The gardening community's "lions, tigers, and bears", these pests can take up residence in your garden soil and cause harm to your plants. Unlike above-ground threats which directly affect your plants, soilborne risks to your garden jeopardize the soil itself, rendering it useless to grow in unless remedied. Fortunately, all you need is a plastic sheet/tarp, the sun, and 4 to 8 weeks to solarize your soil.
(Parasitic nematode affected carrot - Img src: GardenInMinutes)
Solarizing Your Soil
Healthy soil equals a healthy garden, and healthy soil has to be maintained. Solarizing your soil is a non-chemical and effective method for killing soilborne threats by process of capturing radiant heat from the sun to increase your soil's temperature. The increased temperature makes your soil uninhabitable for the soilborne issues, leaving you with healthy soil once complete. It's a simple process comprised of 5 steps:
To trap heat and keep the tarp from sailing – getting buffeted by the wind which cools the soil – the garden needs to have all existing plants removed and soil raked flat. It doesn't need to be perfect, just clear of any chunks of soil or divots that can create air pockets.
Wet soil will heat and retain heat better and than dry soil. By wetting the soil up to 12 inches deep, you are ensuring maximum heat can be reached at deeper levels which will kill or drive away more parasites, fungi, bacteria or pests.
(Garden Grid watering system - Img src: GardenInMinutes)
Transparent/translucent plastic sheeting offers the highest amount of heat production (ideal especially for colder climates), but black plastic sheeting can also be used as it helps control any weed growth as well. Transparent/translucent tarps allow more of the sun's rays through allowing radiant heat to build faster, but in areas where it doesn't get hot enough outside – or sunlight isn't as direct – weeds can grow under it. They won't grow under black tarps though because the black tarps don't allow enough sunlight through for weeds to take advantage. The thickness of the plastic is also important. The most effective will be tarps between 1 mm and 2 mm.
Place the tarp over your soil and make sure it's tight against the soil. This is easiest when covering the soil in a raised garden bed. Since the garden bed is already contained and raised, it's easy to tuck the tarp in between the soil and the garden bed's boards to secure it. If you’re not using a raised bed, find a way to anchor the tarp edges down to ensures it is secure and won't come loose. Once you've tucked it in nice and tight, all soil solarization takes is patience.
After 4-8 weeks (6-8 for colder climates or more problematic soil) of your garden 'solarizing', remove the tarp. Your soil should be rid of the "lions, tigers and bears" and ready for planting!
So the steps are simple, but when you solarize is probably the most important. If you haven't guessed, solarization works best during the hottest time of the year – summertime. From May to August, solarization can heat your soil up to 130 degrees a couple inches deep. In warmer regions, gardeners can solarize their soil up to 18 inches deep, killing a wide variety of threats by leaving no space to hide from the heat. The process can take time, so it's essential to plan. If you want to grow a summer garden, then you may want to consider having a second garden area in the interim. While one solarizes, the other can be filled with all of your favorite vegetables. Then the solarized one will be ready to grow along side it for fall and winter gardening.