Mix 'n' match for success

Growers looking to maximize plant production and ultimately profits know that selecting a good growing media is akin to selecting the right seed. Growers have more choices in a grow mix these days; from pre-mixed growing mediums with “high performance” additives, such as mycorrhizae and biocontrol agents that will help thwart disease, to mixes tailored to specific needs based on particular growing conditions. Some growers even mix their own.

Grow mixes are the foundation for plant support. At a basic level they should provide optimum water retention and good drainage and have pore spaces that allow for good air movement. The nutrient content of the fertilizer is determined by added fertilizers. This foundation for plant growth is important because, after all, it is what’s below ground that we should be interested in, at least in the initial stage of growth.

“For young and upcoming growers, I emphasize that a good mix has to grow roots first, before worrying about the top of the plant,” says Brian Cantin, a 35-year veteran grower and now grower adviser for Berger.
 

Sphagnum peat moss

The main component in a growing media is peat moss. Like petroleum, peat moss is a natural product that is hard to improve upon. Peat from sphagnum mosses have a spongy, fibrous texture, high porosity and water-holding capacity and a low pH. Peats formed from sedges are darker, more decomposed and contain more plant nutrients and higher cation exchange capacity (CEC) than peat from sphagnum (J. Faust and E. Will).

Peat is classified as light or dark. Lighter colored peat is less decomposed and has better aeration and less loss of volume than does the darker, more decomposed peats. Most peats coming from Canada (where most of the peat moss comes from) is classified as a light peat moss. Peat moss makes up from 30 to 60 percent of a growing medium.

“A good quality peat moss gives you good aeration and porosity,” says Cantin. “It is the backbone of a good growing mix.”
 

Perlite

Perlite is volcanic rock that is crushed and then heated to the point of expansion. It helps improve drainage and is a chemically inert substance with virtually zero percent nutrients and a neutral pH. Perlite may contain levels of fluoride that are injurious to fluoride-sensitive foliage plants (J. Faust and E. Will). Maintaining a pH above 6 and reducing the use of fluoride-containing superphosphate fertilizer should avoid fluoride toxicity problems. A good quality peat will reduce the amount of perlite needed in a mix, says Cantin.
 

Vermiculite

Vermiculite is a silicate material that is processed in a similar fashion as perlite. When heated, the vermiculite the particles expand, creating a substance that is porous but able to retain water when used as an ingredient in a grow mix. The finer grades are used for seed germination while the coarser grades are used as a media amendment for the growing on phase of production. Vermiculite is susceptible to compaction. CEC of vermiculite is fairly high. The pH of vermiculite varies from slightly to very alkaline, according to the source of the product.
 

Coir

Coir is a component that is increasingly being used in growing mixes, according to John Bonin, business development and territory manager (Northeast) for Jiffy Products of America, Lorain, Ohio. Coir is a natural fiber from the husks of coconut. The chemical and physical properties of coir are variable, so Bonin says it is important that you purchase it from a company that has knowledge on how to treat coir properly. Bonin says coir that has unbalanced levels of potassium, sodium, calcium, and magnesium ratios can have a direct impact on crop performance

Coir has been suggested as a low-cost replacement for sphagnum peat moss in media. Production trials with a variety of plants indicate that there is great potential for this alternative media component (J. Faust and E. Will).

“Coir, when used with peat, provides fast water uptake and excellent air capacity in air-dried substrate samples,” says Bonin. “Jiffy uses only RHP-certified coir. RHP coir in a mix minimizes compaction issues and is guaranteed to be stable; it doesn’t shrink in normal use.”
 

Handling the media

You can have the best substrate available on the market and fail to maximize its effectiveness by improper wetting and handling. To avoid reducing air space through compaction it is best to wet a media first and then lightly pack it into cell packs, plug trays, and containers. Avoid stacking flats and containers, which would further compact the substrate.

“The moisture level we go for is like that dry fluffy snow that will form a ball and then fall apart,” says Dennis Crum, director of growing operations for Four Star Greenhouse in Carlton, Mich. “By insisting on this moisture level you can lightly pack the media without much settling and still have good anchorage.”
 

Testing

In-house testing is something every grower should be doing, according to Jim Robbins, professor, University of Arkansas Cooperative Extension Service. It’s easy to do in-house, he adds. “The two most critical are pH and electrical conductivity.

You can get instruments for less than $25 each. In Arkansas, we are fortunate that our university laboratory will do both pH and EC for $5, which is hard to beat.” He says their laboratory follows well established procedures for soil-less substrates.

“If you are a grower, you should absolutely have a pH and/or EC meter on-site,” says Robbins. “These are critical tools, just like a calculator. An EC meter should be on hand in case you want to check a fertilizer injector or monitor container fertility.”
 

Price, availability, and consistency

Since most of the peat moss comes from the far reaches of Canada, it is only logical that price fluctuations can occur due to variations in energy costs to ship the product. The other concern growers have in regards to price is additives that go into some mixes. Fertilizer and biocontrol agents can increase the costs of a media.

However, growers understand there can be a corresponding decrease in fertilizer and pesticide costs by using these additives. This is particularly of interest to growers who wish to reduce their use of pesticides or perhaps don’t have the pesticides available due to local, state, or national laws.

For those growers, depending on their markets, there may be fewer choices when it comes to chemical controls, says Ed Blood nick, grower services and product development director for Premier Tech Horticulture, Quebec, Canada. “If you look at the cost of pesticides, it can be pricey. Having a biocontrol incorporate into a mix can be cheaper.”

Consistency of product should be the main concern to growers. Since substrates are natural components with many variables that affect the quality and content of the media, it is important that suppliers can offer grow mixes that are consistent from bag to bag and year to year. This is particularly true of germination media.
 

Mixing your own

Mixing your own media allows full control over what goes into it, allowing you to tailor your mixes to the crop, time of year grown, and the pH of your water source.

“We blend our own mix to meet the needs of our crops at that time of year,” says Four Star’s Crum. He says there are many large growers who do just fine with pre-mixed growing media that is available from suppliers.

However, he said the machine used to pre-mix their own will pay for itself over the years. Four Star has been mixing their own plug and container mix for 21 years; they buy their germination medium pre-mixed.

In regards to the peat moss they purchase to run through their mixing machine, Crum says ensuring consistency in the product is the key.

“A grower wants to look at not only what it looks like coming out of the bag, but what it will be like a couple of weeks later,” says Crum.

An alternative to mixing your own or buying it premixed is to have a company such as Jiffy mix it for you, taking into account your specific growing needs, water analysis, etc. Jiffy is ISO certified, meeting the standards for consistent mixes and environmental and quality controls.
 

Harvesting peat moss

The main component of a growing media is sphagnum peat moss. Peat moss is a species of plant that grows in underwater bogs. Companies such as the family-owned Berger company and Premier Tech, both headquartered in Quebec, Canada, vacuum harvest peat from the bogs. This process, says Berger’s Cantin, is environmentally responsible. Furthermore, he says his company harvests only a very small percentage of the peat moss available in the bogs and then returns the bogs to their former state when finished.

Ed Bloodnick at Premier Tech echoes Cantin’s conviction, adding that Premier Tech is certified by Veri-Flora for environmentally responsible harvesting of peat moss. Both companies’ methods of harvesting peat moss are different than the block-cut method used in Europe. This method has depleted much of the peat bogs throughout Europe, resulting in some bad publicity for the harvesting of peat moss.
 

Select the best

In the end it all comes down to selecting the best growing media for your growing situation.

“While all substrates are not the same, there are several factors that should be reviewed on a growers end before making a business decision,” says Bonin. “They should look at past production history and crop performance, along with their combined years of growing experience to determine what changes are necessary when selecting a substrate manufacturer. When choosing the right mix for their operations, a grower needs to consider several factors: crop pH/EC and nutritional requirements, length of time in production, moisture management control, and the time of the year a crop will be grown.”

“People have to be totally educated on what that product can do and how it should be used,” says Cantin.

Neil Moran is a horticulturist and freelance writer based in Sault Ste. Marie, Mich.

Sources on growing media

Growing Media for Greenhouse Production (PB 1618), Elizabeth Will and James E. Faust, Department of Plant Sciences, University of Tennessee Extension, 2010.

Recommended labs for media testing:

• JR Peters, Allentown, Pa.
• MMI (Micro Macro) International, Athens, Ga.

Testing equipment for in-house media testing:

• Hanna HI 9811-5 pH/EC/TDS meter
• Myron L PT2 and PT 1 Ultra Series of pens

RHP: http://www.rhp.nl/en/professional/