Ask Erik: January/February, 2008
I start my cuttings in trays using small rockwool propagation cubes. I have noticed that a white-looking mold has started to grow on the surface of the cubes and it is starting to grow on the base of the stems of my rooted cuttings. I am worried this will harm my plants. Is there anything I can do to get rid of it?
Molds may occur more readily during propagation if the rooting medium remains too wet, especially if spores are present in your growing environment or on the donor material used to propagate cuttings.
A foliar application of a product containing silicate on the surface of the growing medium and base of the plant will help to rid you of the mold and strengthen the cells of the plant. Plants treated with available silicate will be more resistant to many diseases, insects, temperatures, and drought. Silicate provides a barricade around plant cell walls, and the thickened cells allow the plant more resistant to stresses. Silicate-based products applied to the surfaces of the growing medium and plant will also alter the pH on those surfaces, making them inhospitable to most molds. Applications of silicate may also reduce the incidence and effects of stem rot and other plant diseases.
Although it is important to keep the growing medium moist for non-rooted cuttings, do allow the cubes to dry enough so that they don’t remain saturated for periods of time. If you are using humidity domes, lift them off for a few minutes a day to let things breathe. You can also wipe away any condensation on the lids with a clean paper towel. Under most conditions the cuttings should have rooted before they require additional irrigations from the initial pre-soak/treatment of your rockwool propagation cubes.
Once plants are rooted, make sure there is adequate spacing between cubes so that air can circulate around the growing medium and plants, and allow the top surface to dry out slightly between waterings.
Cheers, Erik Biksa
I am using a specialized nutrient program that has a lot of additives, including beneficials, enzymes, organics, and carbohydrates on top of the base nutrients in the reservoir. My plants are looking great, but there seems to be a mucus-like substance occurring on the sides of the reservoir, and the solution seems a little foamy. I keep the solution well aerated and mixed with a circulation pump and air stones with an aquarium pump. I am not sure what this stuff is. Is it harmful to my plants and what should I do?
What you are likely seeing is biological growth and digestion, which are healthy processes that occur naturally under good soil conditions. The micro-organisms in your beneficial inoculants are colonizing the reservoir and are digesting organic matter in your organic-based nutrient teas and the sugars in your carbohydrate additives.
The specialized microbes are supercharged with the energy sources (organics, carbohydrates) and increased aeration from the circulation pump and air stones. As long as your solution remains well aerated and reservoir temperatures do not exceed 72°F (~22°C) the microbial growth should have no negative effect on the crop. In fact, the healthy microbial activity should help to supply the plants with many substances beneficial to plant growth that may not occur using conventional synthetic fertilizers only.
To help avoid clogging up lines in your hydroponic system you may choose to incorporate a bio-filter into your reservoir. It will help to reduce the amount of “bio-sludge” floating in your reservoir and may further help to promote the bio-activity of your beneficials and the substances they help produce for your crop. A simple and easy bio-filter can be constructed with the use of a natural sea sponge. The physical characteristics of dried and processed sea sponges are ideal for harboring microbial growth and holding and trapping organic residues. Insert an air stone into the cavity of the sea sponge and connect to an airline and air pump. Just drop the aerated sea sponge(s) into your reservoir and keep the air pump on constant. Most of the beneficial growth occurring in your reservoir should gravitate to the sponge. The sponge may look a little grimy over time and should be rinsed occasionally and replaced between crops.
Having a greater degree of biological activity in a media-based hydroponics system can improve your crop. When using non-media systems such as aeroponics, proceed with caution, because there is a higher risk of problems occurring if there is a failure with the system (high temperatures, pump failure, etc.) and the biological activity turns anaerobic. Systems with no growing media can be temperamental because there is no substrate around the roots to buffer activity in the rhizosphere.
Best Regards, Erik Biksa
