Originally Posted by Capt Cannabis
I have been battling pests for the first time during this grow, I believe they are fungus gnats. I have been using neem oil with no improvement. When the plants were younger I put a 1/2" layer of sand on the top of the soil on each plant and the bugs were gone within 48 hours. I was experiencing some issues with yellowing at the time, and I wanted to see what your experiences were when adding sand to your soil. The sand is not from the beach, from a local hardware store.
A few questions regaurding the use of sand:
1) What does sand do to the PH of my soil? Since the sand is on the top, the water and nutrients I give them go through the sand first. How does the top layer of sand affect the PH?
2) Should I do anything to the sand before using? It's coming from a huge pile outside the hardware store.
Any other issues or concerns I should be aware of?
Thanks very much,
My hort professor had some easy steps to help prevent fungus gnats and other soil-born critters.
1. Pour 2 inches of course sand - course so it cuts the soft bodies of the critters.
2. Finely crush some egg and oyster shells and top dress the soil with them - they act as a sharp defense barrier and also they contain up to 98% calcium carbonate so they are a great slow release source of calcium.
3. Then alwayys ALWAYS let your soil dry out in between waterings. gnats love the top couple inches of soil so you will cook their home. I always make sure that 3 inches of my soil is completely dry in between waterings.
I had a bad bag of SEA SOIL that had a ton of bugs. I used the sand technique to first combat the issue then I removed most of the sand and continued with the shells and the drying out of the soil in between waterings and I haven't had a large infection since.
I don't believe it would change the ph. But if left it has the chance to change your soil structure.
One of the best ways to battle them is to add lots of beneficial bacteria and fungi. There are also lots of beneficial predators like mini wasps the lay their eggs in the larvea etc.