Several Pro-Mix blends are suitable for mums, perennials and small nursery containers, including peat/bark blends and peat/chunk coir blends. All Pro-Mix products contain wetting agent to facilitate water absorption and distribution, limestone for pH adjustment and a starter nutrient charge to help plants acclimate after potting. Peat/bark blends are heavier weight products and provide low water retention compared to peat/chunk coir blends that are lighter weight and have high water retention.
For these products, Pro-Mix offers the choice of adding mycorrhizae, which are natural, beneficial fungi that assist plants in the acquisition of water and some nutrients. Mycorrhizae produce more vigorous plants with more prolific flowering. Pro-Mix also offers biofungicide, which is a natural bacterium that suppresses certain root pathogens, including Alternaria, Fusarium, Pythium and Rhizoctonia.
The products recommended for mums and perennials and the ingredients found in each product. The values in each column represent the percentages of each ingredient by volume. O* = optional.
Bark-based growing media
Pro-Mix BRK and BRK20 are Canadian-made growing media with processed pine bark. The bark comes from red pine trees and is partially composted, aged and screened to ½” particle size. Pine bark used for these products is also partially composted, aged and screened to ½” (Pro-Mix BK25) or ¾” particle size (BK45V and BK55). All bark sources are nitrogen stabilized with a carbon to nitrogen ratio of 35:1 (C:N). This is important since a higher C:N ratio can result in nitrogen drawdown during the crop cycle, so higher application rates of nitrogen would be required so that plants would not be deprived. However, this is not the case for these products.
Coir chunk growing media
Pro-Mix HPCC product is made with peat, coir chunks and perlite. Coir chunks are pieces of the coconut husk that have been cut to a particle size of 7-9 mm. What is unique about coir chunks is that they hold much more plant accessible water than bark, while providing extra air porosity and structure for the growing medium. For bark, most of the plant accessible water is found on its surface, while water found within a bark particle is inaccessible to plants, therefore bark has a low water holding capacity. Bark particles also contribute to air porosity and structure, as long as they are not less than <1/8”.
Choosing the right growing medium for your type of crop
Perennials, for example, have specific physical property requirements based on where they are native to. Most plants that have root systems with thick rhizomes (iris) or bulbs (anemone) use water slowly and prefer bark-based growing media that dry out rapidly (Pro-Mix BK25, BRK, BK45V or BK55).
Most perennials have fibrous roots and those such as agastache, columbine, coreopsis, dianthus, gaillardia, lavender, sedum, veronica, etc., prefer a bark-based growing medium that dries out rapidly, such as Pro-Mix BRK, BK45V or BK55.
While other perennials with fibrous roots such as daylily, echinacea, heuchera, hosta, leucanthemum, nepeta, phlox, salvia, etc., prefer a growing medium with higher water retention, such as coir chunk growing media (Pro-Mix HPCC) or a low percentage bark-based growing medium (Pro-Mix BRK20, BK25). For all of these blends, the addition of mycorrhizae favors development of perennials and improves plant quality.
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