The process of flushing your marijuana plants is something cultivators often overlook, even though it's an essential step for producing a crop of clean, smooth tasting flowers. Also known as “leaching,” flushing a cannabis crop can be difference between ending up with fragrant, flavorful marijuana flowers and buds that are difficult to burn and taste harsh.
Flushing helps rid your crop of residual nutrients in the soil (or other growing medium) and forces your cannabis plants to use the nutrients and minerals it has stored as energy reserves. The technique also serves as a way to “reset” your soil if you accidentally over-feed your cannabis plants during the vegetative stage. Whether it's you're first time growing marijuana or it's your first time hearing about this simple step, here we walk you through how to flush a cannabis crop; don't worry, it gets easier with experience!
1. Determine when it's time to flush a cannabis crop. If you begin too early you risk depriving the plants of the nutrients it needs to flourish and waiting too long risks reducing the size of your yield. Flush your cannabis for the last two weeks of the flowering stage to give the plants plenty of time to process excess nutrients. You can also flush your crop during its vegetative stage if the plants have been overfed (called “nutrient burn”) which you can tell by fan leaves that shrivel and turn yellow.
2. You can use plain tap or well water to flush your cannabis crop, but you should check the pH before using the water. If necessary, treat your water supply so make sure the pH is at a safe level for your particular strain(s) of cannabis.
3. Water your plants as normal for the next two weeks, just without the fertilizers or other nutrients you've been feeding your cannabis crop. Flushing your crop doesn't mean water it more often or with a greater volume of water than before, as giving the plants too much water can lead to other problems you don't want to deal with right before a harvest.
4. Use a special meter to measure the amount of total dissolved solids (TDS) that flush out in the water that drains from your cannabis crop. The number should drop from more than 1000ppm to below 100ppm over the next two weeks.