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Contributed by: GyroProtagonist
Submitted: March 2nd, 2005
How to properly clean your dirty old soil!
Disclaimer: I'd like to say that none of the information providedhas been discovered by myself. I just did a lot of research on thesubject because of a number of complaints from fellow soil growersabout fungus gnat infested soil, moldy soil, problems recycling soil,etc.
INTRODUCTION:
Occasionally everyone gets a bad batch of soil...you all know whatI\'m talking about. You\'re finally ready for your transplant so youopen up your bag of rich, organic soil only to find it\'s filled withfungus gnats or some other unwelcome pest. Soil-borne fungi andnematodes can be very destructive to your crops, causing seed rot,seedling diseases, and vascular wilts.
TREATMENTS:
There are various ways to treat soil that is infested. The safestand most popular method is Heat Treatment. Various soil fumigants existwhich create a toxic environment in the soil and will remain toxic fora few weeks or more depending on what kind of fumigant is used.
“Sterilizing” is actually a misnomer, since complete sterilizationwould completely eliminate every living thing in the soil, creating a“biological vacuum”. This “vacuum” would then give an accidentallyreintroduced disease-causing organisms the opportunity to multiply andspread rapidly, causing a severe disease situation.
Instead, treatments can be used that will eliminate the undesirableorganisms, but leave many of the harmless or beneficial soil organisms(called pasteurization). This remaining microbial population willcompete with any introduced troublemaker and help prevent it frombecoming established and spreading rapidly in the treated soil.
Heat Treatment
Temperature control is CRITICAL when heat treating soils.Overheating or under heating can lead undesirable results. Mostdisease-causing fungi are killed by a 30-minute treatment at 140°F.
Plant parasitic bacteria, most plant viruses, and soil insects arekilled at 160°F for 30 minutes, and most weed seeds between 160° and180°F for 30 minutes.
Remember: the higher the treatment temperature, the greater the number of beneficial organisms that will also be killed.
DO NOT OVERHEAT! Chemicals toxic to plant growth can be produced insoils when temperatures reach around 212°F (boiling point of water andtemperature of steam). This more commonly occurs with soils having highorganic matter content. A maximum treatment of 160°F for 30 minutes issuggested.
Oven Method:
Place the soil in containers so that the soil is level, not morethan 4 inches deep. A glass or metal baking pan will work fine. Covereach container tightly with aluminum foil. Place a meat or candythermometer through the foil and into the center of the soil. Set theoven to 160-180°F and heat for 30 minutes after the soil temperaturereaches 160°F. After the treatment, allow the soil to cool.
Note: For large amounts of soil it may not be possible to use anoven. Instead you can use the heat of the sun. First break up the soiland make sure it’s moist. If not, water it and cover with a piece ofplastic. Add more soil around the edges of the plastic to keep it fromcoming loose and letting the moisture and heat out. Leave the soilundisturbed under the sun for a few weeks before planting.
[Editor's note: greenhouses commonly use electric soil sterilizers, able to process larger amounts of topsoil.]
Soil Fumigants
There are various products available for use in outdoor plots thatcan be used when heat treatment is not an option. These products areVERY hazardous and should not be used under any circumstances whereyou\'re plants are already in the plots!
They are for treating unplanted soil and once applied, the areamust be covered with a tarp and left. Aeration times vary. Read thelabel.
Contributed by: AeRoGaNiC
Salts
I just put a post in the grow faq about Cation Exchange Capacity.Read the short little part about Sodium buildup. 15% total saturationis considered borderline toxicity. From what I’ve read Clearex isawesome.
Compost
I have seen research suggesting a high beneficial bacteria andmicro-organism content helps prevent outbreaks from undesired critters.
The technique your talking about to sterilize compost piles iscalled solarizing. You can get more information but I've heard of justputting clear plastic sheeting over the pile.
DO NOT OVERHEAT! Chemicals toxic to plant growth can be produced insoils when temperatures reach around 212°F (boiling point of water andtemperature of steam). This more commonly occurs with soils having highorganic matter content. A maximum treatment of 160°F for 30 minutes issuggested.
Organic matter such as humus or clay have high Cation ExchangeCapacity. If you’ve ever taken chem 100 you know heat accelerates therelease of bonds between ionized metal salts and the medium.
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