Bottoms up

Many people believe wetting agents cause media to hold too much water. However, they actually prevent oversaturation.

From peat to rice hulls, many options are available when it comes to growing media, and several factors play a part in deciding what is best for your growing needs. Here are tips from the experts on choosing the best propagation growing media and soil wetting agents.

Rooted in success
Rooting success relies on a very delicate balance between air and water. When choosing the correct growing media product, it is critical to understand that equilibrium to achieve consistent results during propagation. Several other key factors will help a grower be successful.

First, and most importantly, you can root just about any plant if you balance the air and water of the media properly. Typically, growers have a tendency to over-apply mist during propagation which can delay the rooting of the cuttings. Choosing a growing media with higher air porosity can improve the air-to-water ratio and promote faster rooting. Conversely, media with lower air porosity requires less misting during propagation. In either case, it is critical to never let the cuttings wilt during the initial phase of propagation as it jeopardizes the survival of the cuttings.

Next, there are two main types of propagation growing media: stabilized and loose. Stabilized growing media include foams, peat or polymer-based, paper-wrapped, compressed peat or coir products. By their very nature, stabilized propagation media are bound together as a solid unit and, therefore, do not require an extensive root system to transplant. On the other hand, loose media — which often contain a combination of peat, perlite, vermiculite and coir — require well-formed root systems, and therefore take more time to achieve a transplantable root ball.

The growing media tray influences the microenvironment around cuttings, as well. Select a tray with vent holes that allow airflow around the base of the cuttings to help prevent disease. Also, use a tray configuration that matches the leaf canopy of the crop and avoid over-crowding.

Many growing media manufacturers offer customized options for specific growing needs, from media with different drainage levels, to those with different pH levels. Growers should seek companies that offer a variety of options to fit their needs, as well as those of their specific crops. Plus, growing media manufacturers are always researching ways to help make the lives of growers easier. Flexible, high-efficiency products are always emerging. Some new products have even been purported to reduce propagation cycle time by up to 25 percent.

Finally, consistency is key to any good product. Grower supply specialists glean experience from their customers. Ask which growing media are the most consistent. Word-of-mouth praise about a product is some of the best advice out there. –Brian Cantin

Wetting agents: fact and fiction
A common belief is wetting agents cause a media to hold onto too much water. In reality, wetting agents balance moisture conditions and provide a uniform growing environment.

First, a little of the science behind these products. Wetting agents are added to soilless mixes to ensure water moves uniformly and quickly throughout media.

In untreated media, water repellant components, such as peat and bark, prevent uniform wetting. Irrigation water is repelled by these particles and portions of media will remain dry even after heavy irrigation.

Because wetting agents reduce run-off and run-through, it often appears as though the soil is holding too much water. This leads to the misconception that wetting agents increase water holding capacity. Wetting agents — because they cause water to disperse — allow for better wetting without causing over-wet conditions.

Stabilized media can be transplanted earlier than loose-filled media. Photo courtesy of Smithers-Oasis

Most, if not all, basic plant functions including photosynthesis, plant metabolic functions and gas exchange all tie back to adequate water supply.

Wetting agents assist in controlling water infiltration, water distribution and drainage, thus affecting moisture reserves, nutrient availability and aeration. By preventing water masses from building up, they prevent oversaturation and increase air-to-water ratios in the root zone. If the media remains saturated for a prolonged period of time, the root environment becomes a breeding ground for several root rot pathogens. By maintaining a balanced air-to-moisture level in the media, plant stress is greatly reduced; healthier and stronger plants develop that are more resistant to disease. Consequently, anything that is distributed by water — e.g. pesticides, fungicides and fertilizers — will be more uniformly delivered throughout the media, increasing efficiency of those products.

Recharging the media with a wetting agent prepares the plants for the retail environment. By the end of the production cycle, the water-repellant behavior of certain components can become an issue due to repeated drying in the sometimes harsh retail environment. An application of wetting agent ensures the wetting ability of plants, even when allowed to dry out.

Wetting agents reduce water repellency, improve uniform movement and distribution of water and allow the root zone to maintain the correct level of moisture throughout the growing cycle. This is important for efficient water management in plant production and can also be an important factor in postharvest care and the shelf life of plant material. –Vijay Rapaka

Brian Cantin is a grower advisor at Berger. He holds an Honors Science Degree in environmental horticulture.

Vijay Rapaka is the manager of Grower Research at Smithers-Oasis, an Ohio-based manufacturer of propagation media and floral foam. He holds a doctorate in horticulture plant physiology.