August 06, 2020
When starting out as a medicinal plants grower with all the relative equipment, such as indoor grow tent, indoor grow lights, ventilation,etc, “flushing” is a term you might be unfamiliar with. Although visions of frantically trying to shove a medicinal plants down a toilet may come to mind, flushing is actually when you stop feeding the plants nutrients and simply give them water. The process is generally as easy at it sounds; however, knowing precisely when to flush and how often is a more refined skill.
The act of flushing a plant is using plain water to actively remove any nutrients in the soil. A large amount of water is passed through the soil and drained away on a regular basis. Any minerals and nutrients present in the soil are washed away over time by the water, leaving the soil clean.
Why would you want to strip away all the minerals from the soil? Isn't this hurting your harvest? It actually helps your harvest a significant way. When the nutrients are removed from the soil, it forces your medicinal plants to use up any remaining nutrients still present in the plant. It is a lot like the human body. We take in a lot of food and, what we do not use is turned into fat. In extreme situations where food is scarce, the body relies on this stored fat for energy.
Most experienced growers know how important it is to flush the soil prior to harvesting their plants. What they may not realize is that removing excess nutrients and minerals can be beneficial during other phases of plant growth as well.
Flushing Before Changes in the Feeding Schedule
Many growers flush their plants before switching from vegetative growth formulas to flowering formulas. The reasoning behind this choice is that flushing creates a blank slate. Since plant foods designed for the flowering phase feature different nutrient ratios, adding a liquid food or fertilizer intended for flowering plants to unflushed soil can alter those ratios, leading to overconcentration of some nutrients and minerals and under-concentration of others.
Some growers also flush their plants when they switch from seedling food to vegetative phase food. Novice growers who haven’t gotten a feel for how hardy their plants are at different stages of growth should be careful if they choose to follow suit, though. Seedling medicinal plants in air grow pot or others have small, poorly developed root systems, so over-watering can cause them to become unstable in the soil.
Flushing Before Harvest
While it’s not strictly necessary to flush plants before switching to a new plant food or liquid fertilizer, pre-harvest flushes are essential. Not only will flushing before harvest improve the taste of growers’ harvested flower by removing excess chemicals and nutrients, but it will also stimulate growth in the flowers.
There are two mechanisms at work behind this stimulation in growth. First, flushing the plants causes mild stress, which tells the plants to invest their energy in rapid growth in an effort to reproduce.
Flushing, or removing, the excess nutrients and minerals from the soil also encourages plants to use up the nutrient stores that have built up in their cells throughout the growing season. The use of those nutrients stores route to the flowers, encouraging a growth boost to the flowers during this final phase. The result will be increased bud growth and a lower concentration of unused nutrients, which is what explains the difference in taste that occurs when growers flush their plants pre-harvest.
When performing a pre-harvest flush, growers need to pay attention to the maturity of the flowers because timing is important. The mature flower will have dark orange or amber pistils and opaque trichomes. Flushing the plants too early will rob them of the nutrients they need to fully develop, while flushing them too late will leave a concentration of excess nutrients in the final product. Instead of following generalized rules of thumb like flushing two weeks before harvest, check on the plant’s trichomes to determine when the time is right.
Plants with mostly clear trichomes are in the perfect stage for flushing. By the time the plants are harvested, the trichomes should be milky and white. By then, it’s too late to flush the soil. For best results, stop feeding the plants and flush them as soon as the first trichomes begin to change color.
Whether they're autoflowering, quick, CBD-rich, indica or sativa hybrids, all medicinal plants can be flushed using the same method, which involves two complementary techniques: flushing of the substrate and flushing through watering.
This first stage is aimed at removing the salts built up in the substrate, and should occur at least three weeks prior to the end of the flowering period.
For an optimal result, set your pots in a shower or bathtub and pour water onto the top of the soil for 25-30 minutes. You just have to hold the showerhead above the pots, interrupting the flow of water at short regular intervals so that it drains from the bottom of the pot, gradually cleaning the substrate. The drained water will be rather dark at first, but should become clearer and clearer as the substrate gets clean. By the end of the process, the water should come out clean.
A good way to ensure everything has gone as expected is to measure the EC of the water drained from the pot both at the beginning and at the end of the process. By doing so, you won't have to rely just on the colour of the water, but will also have tangible data to help you -high at first, the EC value should be greatly reduced after flushing. Besides helping you determine whether the plants have been correctly flushed, measuring the EC is a great way to gain awareness of the amount of waste that can end up in your body if you ingest buds from plants that have not been flushed.
For a particularly thorough result where the final product is completely safe and free from impurities, you can reflush your plants after a week, reducing the flushing time to 15-20 minutes.
This is the preferred method by medicinal plants growers.
Flushing through watering is a method that essentially involves giving your plants abundant clean water - with a pH of 6.5 - during the last 2-3 weeks prior to harvest. Enzymes may be added to the water once or twice a week to aid the dissolution of minerals built up in the roots and tissues of the plant.
A three-week flushing will completely remove excess mineral buildup from your plants, ensuring the final product is entirely free from impurities. If you opt for a flushing of just two weeks, instead, your medicinal plants will be sufficiently clean but will probably contain a small amount of salts.
During senescence, the last maturation stage of the flowers before harvest, plants start to yellow, gradually losing their intense green colour. Surprisingly enough, this is a very positive sign that everything is going as expected and that the plant tissues are effectively absorbing and assimilating the nutrients.
Hopefully these tips will help you improve the quality and the safety of your crop. Best of luck with your grow!Once you’ve properly flushed and harvested your garden, it’s important to dry and cure the medicinal plants correctly. It is through a quality flush and a long cure that your medicinal plants will be able to fully express itself.