Growing Media For Horticultural Production Scott Poague, Holtville High School

Properties Of Growing Media Growing media consists of mixtures that provide water, air, nutrients, & support to plants. Growing media is not considered soil. 4 main factors affect air & water status in nursery containers The media components & ratios Height of the media in the containers Media handling Watering practices

Media Handling The major concern is to avoid compaction. Growing containers should never be stacked when filled with media. Moisture content is also important. Adding water to peat-based mixes before filling trays causes the media to swell & helps create more aeration.

Media pH Initial pH of growing media should be between 5.8 & 6.2. Most media components are acidic, so dolomitic lime is added to start at an acceptable pH range. Commercially blended media typically have limestone already incorporated. If you mix your own, lime is added at a rate of 10-15lbs. per yard.

Media Components Most greenhouse media contains 30-60% peat moss in combination with other materials. Various materials are added for water drainage & aeration.

Peat Main component of soil-less media mixes. Produced by partial decomposition of plant material under low-oxygen conditions. Peats from sphagnum mosses have a spongy, fibrous texture, high porosity & water holding capacity.

Bark Byproduct of sawmills, & used extensively by nursery industry. Must be aged or composted before use. Low nutrient value

Coir Originates from ground coconut husks. Contains low levels of micronutrients, but higher levels of phosphorus & potassium.

Perlite Volcanic rock that is crushed & heated rapidly to a high temperature. White, light weight w/ high pore space. Added to improve drainage.

Vermiculite Silicate material that is processed much like perlite. Available in a number of grades. Particles are soft & easily compressed, so must be handled carefully.

Cow Manure Heat treated & dried to kill bacteria & weed seed. Adds various micronutrients to media mix.

Wood Shavings/Saw Dust Used as a water holding agent. Very little nutrient value.

Mixing Your Own Media Purchasing commercial mixes is based primarily on production cost. As a rule of thumb it is not economical to mix your own media with less than 100,000 square feet of growing space. Mixing equipment can range from sophisticated, expensive equipment to a cheap cement mixer.

Commercial Formulations Most common media used, are mixtures of peat, vermiculite, & perlite. Designed to achieve high porosity & water retention with adequate aeration. Formulations w/o wetting agents are available for growing sensitive plants like seedlings.

Mixes We Use

References www.farmphoto.com Growing Media for Greenhouse Production, University of Tennessee