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 provided
has been discovered by myself. I just did a lot of research on the
subject because of a number of complaints from fellow soil growers
about fungus gnat infested soil, moldy soil, problems recycling soil,
etc.
INTRODUCTION:
Occasionally everyone gets a bad batch of soil...you all know what
I\'m talking about. You\'re finally ready for your transplant so you
open up your bag of rich, organic soil only to find it\'s filled with
fungus gnats or some other unwelcome pest. Soil-borne fungi and
nematodes 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 safest
and most popular method is Heat Treatment. Various soil fumigants exist
which create a toxic environment in the soil and will remain toxic for
a few weeks or more depending on what kind of fumigant is used.
“Sterilizing” is actually a misnomer, since complete sterilization
would completely eliminate every living thing in the soil, creating a
“biological vacuum”. This “vacuum” would then give an accidentally
reintroduced disease-causing organisms the opportunity to multiply and
spread rapidly, causing a severe disease situation.
Instead, treatments can be used that will eliminate the undesirable
organisms, but leave many of the harmless or beneficial soil organisms
(called pasteurization). This remaining microbial population will
compete with any introduced troublemaker and help prevent it from
becoming 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. Most
disease-causing fungi are killed by a 30-minute treatment at 140F.
Plant parasitic bacteria, most plant viruses, and soil insects are
killed at 160F for 30 minutes, and most weed seeds between 160 and
180F 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 in
soils when temperatures reach around 212F (boiling point of water and
temperature of steam). This more commonly occurs with soils having high
organic matter content. A maximum treatment of 160F for 30 minutes is
suggested.
Oven Method:
Place the soil in containers so that the soil is level, not more
than 4 inches deep. A glass or metal baking pan will work fine. Cover
each container tightly with aluminum foil. Place a meat or candy
thermometer through the foil and into the center of the soil. Set the
oven to 160-180F and heat for 30 minutes after the soil temperature
reaches 160F. After the treatment, allow the soil to cool.
Note: For large amounts of soil it may not be possible to use an
oven. Instead you can use the heat of the sun. First break up the soil
and make sure it’s moist. If not, water it and cover with a piece of
plastic. Add more soil around the edges of the plastic to keep it from
coming loose and letting the moisture and heat out. Leave the soil
undisturbed 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 that
can be used when heat treatment is not an option. These products are
VERY hazardous and should not be used under any circumstances where
you\'re plants are already in the plots!
They are for treating unplanted soil and once applied, the area
must be covered with a tarp and left. Aeration times vary. Read the
label.
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 saturation
is considered borderline toxicity. From what I’ve read Clearex is
awesome.
Compost
I have seen research suggesting a high beneficial bacteria and
micro-organism content helps prevent outbreaks from undesired critters.
The technique your talking about to sterilize compost piles is
called solarizing. You can get more information but I've heard of just
putting clear plastic sheeting over the pile.
DO NOT OVERHEAT! Chemicals toxic to plant growth can be produced in
soils when temperatures reach around 212F (boiling point of water and
temperature of steam). This more commonly occurs with soils having high
organic matter content. A maximum treatment of 160F for 30 minutes is
suggested.
Organic matter such as humus or clay have high Cation Exchange
Capacity. If you’ve ever taken chem 100 you know heat accelerates the
release of bonds between ionized metal salts and the medium. |