Soilless Mix

Marijuana Horticulture

by Jorge Cervantes

Soilless mixes are very popular, inexpensive, lightweight, and sterile growing mediums. Commercial greenhouse growers have been using them for decades. The mixes contain some or all of the following: pumice, vermiculite, perlite, sand, peat moss, and coconut coir. Premixed commercial soilless mixes are favorites for countless growers. These mixes retain moisture and air while allowing strong rot penetration and even growth. The fertilizer concentration, moisture level, and pH are very easy to control with precision in soilless mix.

Soilless mixes are the preferred substrate for many bedding plant and vegetable seedling commercial growers. Soilless mixes have good texture, hold water, and drain well. Unless fortified with nutrient, soilless mixes contain no nutrients and are pH balanced near 6.0 to 7.0. Coarse soilless mixes drain well and are easy to push plants into growing faster with heavy fertilization. The fast0draining mixes can be leached efficiently so nutrients have little chance of building up to toxic levels. Look for ready mixed bags of fortified soilless mixes such as Jiffy Mix, Ortho Mix, Sunshine Mix, TerraLite, and ProMix, etc. To improve drainage, mix 10-30 percent coarse perlite before planting. Fortified elements supply nutrients up to a month, but follow directions on the package.

Soilless components can be purchased separately and mixed to the desired consistency. Ingredients always blend together best when mixed dry and wetted afterwards using a wetting agent to make water more adhesive. Mix small amounts right in the bag. Larger batches should be mixed in a wheelbarrow, concrete slab, or in a cement mixer. Blending your own soil or soilless mix is a dusty, messy job that takes little space. To cut down on dust, lightly mist the pile with water several times when mixing. Always wear a respirator to avoid inhaling dust.

The texture of soilless mixes – for rapid growing cannabis – should be coarse, light , and spongy. Such texture allows drainage with sufficient water and air retention, as well as providing good root penetration qualities. Fine soilless mix holds more moisture and works best in smaller containers. Soilless mixes that contain more perlite and sand drain faster, making them easier to fertilize heavily without excessive fertilizer salt buildup. Vermiculite and peat hold water longer and are best used in small pots that require more water retention.

The pH is generally near neutral, 7.0. If using more than 15 percent peat, which is acidic, add appropriate dolomite or hydrated lime to correct and stabilize the pH. Check the pH regularly every week. Soilless mixes are composed mainly of mineral particles that are not affected by organic decomposition, which could change the pH. The pH is affected by acidic fertilizers or by water with high or low pH. Check the pH of the runoff water to ensure the pH in the medium id not too acidic.