Perlite Not Good For Container Blueberries
Container production of blueberries is becoming more popular because it allows increased control of the rooting media. High organic matter and low pH are more easily maintained in containers than in Florida soils, but water retention can be a problem. Peat or coir substrate are typically used for container production. Perlite, a stable expanded volcanic mineral, is often added to increase drainage in potting mixes. However, blueberry performance in various substrates is not that well documented. Researchers in Oregon, working with highbush blueberries, wanted to test plant responses to various amounts of perlite added to peat and coir based potting media.
‘Liberty’ northern highbush blueberry and ‘Jewel’ southern highbush blueberry liners were planted into 16 different media treatments. The treatments included four rates of coarse perlite at 0%, 10%, 20% or 30% by volume combined with sphagnum peat, coconut coir, or a 2:1 or 1:2 mix of peat and coir. Plants were grown in a climate-controlled greenhouse, fertigated daily with a weak fertilizer solution, and irrigated to maintain drainage at about 25% of the total volume of solution applied as well as supplemental irrigation to keep the pots from drying out. After 95 days the plants were destructively harvested and divided into roots, stems, and leaves. Plant parts were dried for dry weights and tissue nutrient analysis. The media was also analyzed for nutrients before, during, and after the experiment.
‘Liberty’ plant dry weight was greatest in pure peat and progressively less with the more perlite or coir added. ‘Jewel’ plant dry weight also decreased with increasing amounts of perlite, but was unaffected by the ratio of peat and coir. Perlite did not seem to affect pH or nutrition and more likely affected the plants through media water content. Higher amounts of peat in the media mix increased plant uptake of nitrogen, phosphorus, magnesium, and sulfur and decreased the uptake of potassium, boron, zinc, and sodium. Higher amounts of coconut coir in the media increased the concentrations of sodium and chlorine.
High amounts of perlite in blueberry potting media may reduce growth, possibly by creating too much drainage. Some highbush blueberry cultivars may grow better in peat than in coir.
P.H. Kingston, C.F. Scagel, D.R. Bryla, and B.C. Strik. 2020. Influence of Perlite in Peat- and Coir based Media on Vegetative Growth and Mineral Nutrition of Highbush Blueberry. HORTSCIENCE 55(5):658–663.