1. Use growing media shortly after blending or delivery.
Growing media does not go bad, but changes do occur with aged product. Changes include draw-down of certain nutrients (if the blend has a starter nutrient charge), activation of limestone and decreased effectiveness of the wetting agent. For example, wetting agents can be consumed by native microorganisms found in the growing media components and can chemically degrade.
Microbes in the growing media can potentially consume the fertilizer charge, especially nitrogen and iron. This may explain why crops planted in aged growing media get off to a slower start. These processes occur more rapidly with hot storage temperatures than with cold.
Product aging begins the day the growing media is manufactured. Most manufacturers print a manufacturing date on the package. If you use packaged growing media, check with the manufacturer for this date. If you mix your own, keep records for the day you mixed it. The best use of a typical packaged peat-based growing media is eight to nine months during the summer months and 10 to 12 months through colder, winter months. Growing media components that have been composted contain a high population of microorganisms that can also consume the wetting agent. Therefore, packaged growing media containing bark and compost have a shorter best-use date of four to six months.
Some additives incorporated into growing media are more critical for the best-use date. Growing media that contain controlled-release fertilizers should be used within one month of the manufacturing date due to the release of fertilizer within the package. Some fungal-based biofungicides have a shelf life of a few months when incorporated into the growing media; however, most bacteria-based biofungicides and mycorrhizae can last more than a year.
The take-home message for aged product is that you may need to modify your cultural practices when planting in an older growing media. The best way of knowing how to use aged product is to send unused samples to a laboratory for testing and discuss recommendations with the media manufacturer.
2. When switching to a new growing media, expect to water differently.
The most difficult change to overcome is the water requirements. Select a growing media that has similar watering characteristics to what is currently being used. Having the same appearance when it dries out is also ideal, as many growers use the color of the growing media to determine when to water. The adjustment is often difficult for the employees who are most familiar with the current growing media.
Other considerations when switching include:
- Will there be changes required in my fertility program?
- Will the growing media influence the application rate of plant growth regulator drenches?
- How will the limestone react and change the pH of the growing media?
- How will the buffering capacity of the growing media be affected by the limestone?
- Keep in mind that switching growing media may not always be a solution to a growing problem.