Q. Earlier in March you
talked about fungus gnat problems in potting soils. You recommended baking the
potting soil in the oven. But I’ve heard this stinks up the whole house! I
might try it in a gas grill outside, but not inside.
talked about fungus gnat problems in potting soils. You recommended baking the
potting soil in the oven. But I’ve heard this stinks up the whole house! I
might try it in a gas grill outside, but not inside.
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| Potting soils are lightweight soil mixes that usually contain peat moss and perlite as part of the soil component to minimize weight and maximize porosity. |
A. I used to think the
same thing about baking potting soil in the oven. The common response by
gardeners is not to do it for that very reason; it stinks up everything! But we
tested it recently and it worked just fine as long as the temperature of the
oven was below 180F. I think the smell problem occurs when the temperature of
the oven is set too high.
same thing about baking potting soil in the oven. The common response by
gardeners is not to do it for that very reason; it stinks up everything! But we
tested it recently and it worked just fine as long as the temperature of the
oven was below 180F. I think the smell problem occurs when the temperature of
the oven is set too high.
I prefer “solarizing” potting soil in sealed, clear
plastic bags for a couple of days to kill fungus gnats. The temperature of the
soil does not have to be as high as it does to kill everything in the soil,
a.k.a soil sterilization. If the temperature of the potting soil reaches 140 –
150 F for 30 minutes, through and through, it’s enough to kill insects.
plastic bags for a couple of days to kill fungus gnats. The temperature of the
soil does not have to be as high as it does to kill everything in the soil,
a.k.a soil sterilization. If the temperature of the potting soil reaches 140 –
150 F for 30 minutes, through and through, it’s enough to kill insects.
To sterilize potting soil, completely ridding it of all
insects as well as harmful microorganisms, the temperature must reach 180° F
for 30 minutes throughout the soil. Attaining this temperature by solarizing is
doable if there is plenty of sunshine, the soil is moistened, placed in a clear
plastic bag and left in the sun long enough.
insects as well as harmful microorganisms, the temperature must reach 180° F
for 30 minutes throughout the soil. Attaining this temperature by solarizing is
doable if there is plenty of sunshine, the soil is moistened, placed in a clear
plastic bag and left in the sun long enough.
To be on the safe side, I solarize the soil with one side
facing the sun the first day. Then I turn the bag over and solarize the other
side on the second day. I check the temperature with a temperature probe
through the plastic bag to make sure the temperature was high enough.
facing the sun the first day. Then I turn the bag over and solarize the other
side on the second day. I check the temperature with a temperature probe
through the plastic bag to make sure the temperature was high enough.
I would not recommend putting potting soil in a gas grill
and firing the temperature up high. Low temperatures in gas grills are harder
to control. Excessively high temperatures will “burn up” the organics in the potting
soil. That’s when it gets stinky.
and firing the temperature up high. Low temperatures in gas grills are harder
to control. Excessively high temperatures will “burn up” the organics in the potting
soil. That’s when it gets stinky.
This cool, overcast spring presented some real problems. Cool
temperatures and overcast skies did not allow solarization to reach the
temperatures needed inside the bag. I enlisted the aid of a brave volunteer
with an oven that had accurate temperature controls. She placed a half bag of
potting soil on cookie sheets and into a domestic oven.
temperatures and overcast skies did not allow solarization to reach the
temperatures needed inside the bag. I enlisted the aid of a brave volunteer
with an oven that had accurate temperature controls. She placed a half bag of
potting soil on cookie sheets and into a domestic oven.
The lowest thermostat setting for the oven was 160° F.
The temperature inside the oven stayed around this temperature for 30 minutes
and the soil allowed to cool inside of it. Voilà. No fungus gnats and no off smell.
The temperature inside the oven stayed around this temperature for 30 minutes
and the soil allowed to cool inside of it. Voilà. No fungus gnats and no off smell.