Media Selection — Reality Speaks By Hugh A. Poole

Growers are fortunate that plants are adaptable to a wide range of media combinations and properties. Every crop cannot be grown in the ideal mix under the same roof. A grower cannot be expected to have dozens of mixes for his numerous crops. Unlike operations in Europe, where monoculture is the rule, North American growers produce many different crops and must compromise to be successful.

The reality is that growers make their media decisions based on three factors: cost, availability or ease of purchase and crop performance. Cost is often the major criterion for the purchase decision. Other growers prefer the ease of purchasing their soil mix from a reliable mix supplier. Other growers place greater importance upon consistent performance of their crops. The final decision by the grower is usually a blend of the above reasons based upon his comfort level.

Mixing It Up

Grower mixes are a combination of factors beyond the raw ingredients. Most mixes are a combination of two or more components blended to provide the proper aeration, moisture control and nutrient retention for the longevity of the crop. Historically, the optimal mix for many crops has contained three components to meet these requirements. The old soil mixes contained field soil, peat moss and perlite. The Cornell peat-lite mixes often consisted of peat moss, perlite and vermiculite. Today's bark mixes combine bark, peat moss and either perlite or vermiculite. Even the European peat mixes are often a blend of two or more grades/sizes of peat moss.

Today's mixes are combinations of the following ingredients: peat moss, perlite, vermiculite and aged/composted bark. Depending on availability, coir, rice hulls, pumice, calcined clay and a variety of local ingredients may be substituted for the more common ingredients. The choice of ingredients is determined predominantly by whether the grower makes it himself or purchases the mix from a mix supplier.

The source of the mix dictates the choice of ingredients and cost. The grower feels that he has the most control of costs and the quality of the mix by purchasing the raw materials himself and having the mix produced on site, under his direction. To produce his own mix, he must purchase a mix-line and dedicate a warehouse to house the equipment and raw materials. He must purchase the raw materials and all media amendments, including limestone, wetting agent and fertilizers. His production line needs to have sufficient capacity to meet his anticipated peak mix requirements. He also needs to dedicate reliable personnel to produce a satisfactory mix, maintain good quality control procedures and do it in a timely and consistent manner. Assuming that he has sufficient equipment, he has maximum flexibility but his staff carries all of the risk.

Peat-lite formulations can be purchased in compressed bales and delivered directly from a manufacturing facility. Bales are usually 3.8, 55 or 110 cu.ft. compressed by a factor of 2:1 in most cases. To minimize transportation costs, there is very little advantage of having more than 240 cu. ft. of fluffed mix or peat on a pallet. Although transportation costs and the Canadian dollar have increased dramatically, a baled mix is often the most cost-effective means of filling pots. Most mixes are combinations of peat moss, perlite and vermiculite, but a grower can have his mix customized to his specifications by changing percentages of raw materials or amounts of soil amendments.

Another option that some growers use is to use a baled peat-perlite mix with appropriate amendments as a base ingredient to use with locally available bark, rice hulls or coir. He has the benefits of the bale mix and the option to mix his final growing medium as well. The precise addition of amendments can be controlled by qualified technicians and laboratory testing.

European peat mixes are also available in "towers." These are blends of specially screened peats that have been amended and are intended as standalone mixes to grow plants. This is a common practice in Europe, where few other ingredients are used. Growers have to learn how to "grow" in these new media to be successful.

Purchasing in Bulk

If a grower is located close enough to a mix producer, he may be able to purchase his mix in bulk. Generally, bulk delivery makes sense if the grower is within 300 miles of the plant so that a "live-bottom" truck can deliver from the plant without an overnight stay to reduce transportation costs. The grower must provide a pad or storage barn for delivery and have a bucket loader to fill the hoppers as needed. As transportation cost is by the trip, it helps to maximize the number of yards in a truck. The plant may ship 100 cu.yd. of a light- or medium-weight mix but only 75 cu.yd., or less, of a heavyweight mix.

The major cost savings with a bulk delivery is the absence of costly plastic bags and pallets and their disposal costs. Heavy bark mixes for perennial and nursery crops are often produced in bulk. The professional mix plant can customize mixes with requested ingredients and amendments. However, large grower operations can use a lot of truckloads in a very short time. Scheduling and logistics are major concerns.

The other common delivery method for growing media is loose-filled bags. These bags may be 2.8 cu.ft. plastic bags or 60 cu.ft. tote bags. These bags can be palletized for ease of shipping and safely stored indoors or outdoors. Freezing can be an issue if stored outdoors, but bags will thaw faster than bales. This delivery method is more costly than baled mixes because fewer cubic feet of mix are transported on a truck and there is more plastic per cubic foot of mix. However, this is the most convenient form of delivery and does not require a bale buster. The mix moisture is sufficient that containers can be filled directly out of the bag with minimum dust. Customization of the mixes is easily accomplished in bags with changes in either the ingredients or amendments. Upon request, we can even change the volume of the bags, the number of bags per pallet or even the color of the bags.

Customized Orders

Ideally, we would like to customize the mix to the specific needs of the crop, but that is not realistic in a typical greenhouse operation. The grower is often making compromises for the crop, weather, water quality or needs of the operation. Reality dictates that the grower minimize the number of media in the greenhouse. He may have a propagation media, a greenhouse growing mix and possibly an outdoor perennial mix. Many growers have only one growing mix, regardless whether he mixes his own or buys it off the shelf. Some growers may use the same mix in regards to ingredients but alter the limestone rate for specific crops.

Since the mix cannot be customized to the plant, it is left to the grower and his staff to make the necessary adjustments during production to provide for the crop. Just as a reliable employee is easy to work with, a consistent growing mix can simplify the work of the production staff. Automatic watering systems can reduce variability within a crop if the mix is consistent. A vigilant production staff can make adjustments for specific crops before it is too late if the mix is consistent.

You Make the Call

If the grower chooses to make his own mix, he must invest in the equipment, facilities and personnel to do the job right every time. If he chooses to purchase a mix, then he must be concerned with the consistency of the growing mix, customer service, delivery issues and technical support in the field. If he chooses to customize his mix with a biological product, polymer, controlled-release fertilizer or a different ingredient, such as rice hulls or coir, he must ask himself whether it can be done correctly.

Regardless of the media source, it is critical that the production staff address any problems with media, irrigation practices or fertility program promptly before they become serious. The grower should use whatever consultants, laboratories or technical sources are available to his staff. Cost may not be the determining factor for success.

Hugh A. Poole

Hugh A. Poole is director of technical services/quality control with Conrad Fafard, Inc. He can be reached at

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