Mixing it up for premium produce

Greenhouse managers who grow vegetable plugs and transplants for field production and retail markets know that a quality growing medium is essential for greenhouse production. However, many might rely on the same mixes for vegetable production and ornamental production. What they may be missing out on is the better control they can get from a mix designed specifically for vegetable plugs and transplants.

Regardless of what growing mix you ultimately choose, or choose to mix yourself, it should provide optimum water retention, good drainage, and have sufficient pore space to allow for adequate air movement. From there it is important to understand what nutrients can do for your vegetable plugs and transplants and how to avoid too much of a good thing.

“A good mix will be dense enough to support the seedling, retain moisture, be porous for good drainage, free of plant pathogens, and have a pH of 6.5 to 7 and enough nutrients to last until you wish to begin using fertilizer,” says Pam Carter, greenhouse manager for Johnny’s Selected Seeds, a vegetable seed supplier out of Albion, Maine.
 

Basic mixes

Whether they’re formulated for vegetable or ornamental crop production, all greenhouse blends will feature sphagnum peat moss as the major component. Peat from sphagnum mosses has a spongy, fibrous texture with high porosity and water-holding capacity, and low pH. Peat will be either light or dark. Light colored peat is less decomposed and has better aeration and less loss of volume than does the darker stuff. Peat moss makes up 30 to 60 percent of a growing medium.

Coir, an alternative to sphagnum peat moss, is increasingly being trialed and used in greenhouses, according to John Bonin, business development and territory manager (Northeast) for Jiffy Products of America in Lorain, Ohio. Coir comes from the husks of coconut. Bonin says the nutrients in coir are variable, which should be taken into account when using this product. In the future, growers may use coir as a low cost alternative to peat.

Perlite and vermiculite are other components of a mix. Perlite is volcanic rock that is crushed and then heated to the point of expansion. Perlite helps improve drainage and is a neutral pH component with virtually no nutrient value.

Vermiculite is another component in a mix, though not all mixes contain vermiculite. It’s a unique component in a blend because it is water retentive yet porous. The finer grades can be used for seed germination, and coarser blends to grow on and finish a crop.
 

Major and minor nutrients

It is important to know what nutrients are in a mix and how long they will be available to the plants, so that you can schedule your fertilization program accordingly.

Nitrogen, when added to a mix, provides a kind of “get up and go” in the early stages of growth, and encourages early greening up and initial thick stem development. Some mixes have only enough nitrogen in the mix for the first week or so of development. Too much nitrogen will cause soft tissue growth and intermodal stretch in developing transplants. Soft tissue growth is attractive to phloem-feeding insects such as aphids. These plants may also be more susceptible to foliar blights as well.

Phosphorous is often associated with bloom initiation but is also responsible for root development. Because it doesn’t leach away as quickly as nitrogen, the formulation in a mix may make this nutrient available longer than nitrogen. Phosphorous, as part of a fertility program, will result in a moderate increase in transplant height, stem diameter, and dry weight. A phosphorous deficiency will be evident by a conspicuous purpling of the leaves, stems, and stunted plants.

To ensure good disease resistance and overall plant hardiness, be sure your mix or fertilization program includes proper amounts of potassium, as well as minor nutrients like boron and zinc. Familiarity with the blend ensures the recommended amount of nutrients will be available to your plants without resulting in toxicity problems, excessive growth, etc.
 

Grow mix for vegetable transplants

Perhaps the best option for vegetable transplant growers is to use a growing mix specifically formulated for vegetable production. Companies like Jiffy are stepping up to provide growers with what they need to be successful right out of the gate.

“Growers are looking for control over their crop.” says Jiffy’s Bonin. “Our mixes give growers a little more control over the crop at the start. If you start with a good growing medium, you’ll finish with a great plant or transplant.”

Bonin says you have to know what you’re looking to get out of a growing mix. This means “building backwards.” That is, knowing your water quality and alkalinity, including the use of fertilizers used at your facility, as well as performing seasonal checks on your injectors or other equipment. “Make sure your equipment is running properly to minimize or reduce those incremental costs,” he advises.

He says Jiffy can help the grower by custom blending vegetable mixes that will minimize pH “drop” and “creep,” in other words: situations where the pH can rapidly change due to water quality and type of fertilizers used in production. They can also add the right amount of Jiffy’s own proprietary fertilizer so that plants will get a good start, with a final grower application a few days prior to shipping. “This means a blend that is lower, or minus nitrogen, but has all the essential minors included, like with #14 and #24 that may help with those top-selling veggies across areas of vegetable production.”

Growers looking to purchase greenhouse mixes for vegetables should let the supplier know what the pH of their water is and what they need the pH of the mix to be to grow the specific crop or crops. Suppliers should be willing to work with you to achieve this objective, or look for one who will.
 

Nutritional disorders

Vegetable transplants can have the same nutritional problems as ornamental plants, particularly with nitrogen toxicity and deficiency. Serious problems can occur in early production.

Here are a few things to watch for: high soluble salts, ammonium toxicity, and trace element toxicity. Soluble salt problems usually occur shortly after transplanting from plug trays to cell packs. Know what is in your mix and coming out of your injectors to avoid the problem of soluble salt toxicity. Here is where a mix specific to vegetable crops can help prevent this problem.

Trace element toxicity may appear with crops such as tomatoes, when iron (Fe) and/or manganese (Mn) levels rise too high. Numerous small dark spots and mottling of foliage are tell-tale signs. The causes of this form of toxicity can be contributed to trace elements in the mix itself, water-soluble fertilizers with elevated trace elements levels, and even irrigation water (T. Smith and L. Pundt).

Ammonium toxicity can be a problem with veggies crops, particularly tomato, eggplant, and pepper. Regular testing of substrates is recommended to avoid this and other nutrient problems.
 

Organic mixes and additives

Some growers have chosen to go organic in their plant production. A straight-run mix of sphagnum peat moss, vermiculite, and perlite should meet standards for organic production, though it’s wise to check with your certification source or board to be sure.

“A grower should always work with their certifier, as every agency can be different. The OMRI (Organic Materials Review Institute) website is helpful,” says Carter.

Greenhouse growers looking to use OMRI-approved products have a few options from which to choose. It’s best to do research to see which options meet the nutrient needs for your crop, and also if there are any toxicity concerns in using them.

Dr. John Biernbaum, professor with the Department of Horticulture at Michigan State University, uses a 50/50 mixture of peat and compost with a pH of 6.0 as an organic potting media in his research. The compost comes from decomposed straw, garden waste, hay, and sheep/horse manure.

UMass Amherst researchers say the chemical composition of compost varies from batch to batch, so they suggest that whatever compost you use (purchased or home brewed) let stand for six months allowing nutrients to stabilize, phytotoxic compounds to degrade, and disease suppressive beneficial microbes to have a chance to do their thing. The researchers go a step further and recommend using only 20 to 30 percent compost, depending on the crop being grown. And, of course, test, test, and test!

Organic products can be added to build fertility in the mix. Dr. George Elliott, at the University of Connecticut, recommends adding a “commercial pelleted” organic fertilizer to a standard mix. Liquid organic fertilizers are also an option, and can be relied on to meet nutritional standards for healthy plant growth. However, researchers note that fish emulsion supplies mostly ammonium nitrogen, which can be toxic to some plants. Also, fish emulsion is hard to keep on hand in the greenhouse for long periods of time because it tends to mold. Netune Harvest manufactures OMRI-approved fertilizers for organic greenhouse growing.

“I use fish fertilizer, when I have to use OG (organic),” says Johnny’s Selected Seeds’ Carter.  

“[It’s] smelly, but effective.” Carter adds this to Johnny’s JSS 512 mix, sold bulk in 2-yard bales.

Other organic products, such as Pinnacle 3-1-1 and Biolink 3-3-3, are still being studied for effectiveness in greenhouse organic production.
 

Knowledge is key

The goal of vegetable growers is to grow compact, healthy plants in short periods of time with as few inputs as possible. And a thorough understanding of what goes into your mixes plays a key role in achieving success.

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

For more:

• Johnny’s Selected Seeds: www.Johnnyseeds.com
• Premier Tech: http://www.pthorticulture.com
• Berger: http://www.berger.ca
• Jiffy Products of America: http://www.jiffygroup.com