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What we know, and what we should know, about blueberry production in soilless substrates

Gerardo H. Nunez

Blueberry bushes are notorious for their strict soil requirements. Optimum growth is frequently observed in well-drained acidic soils (pH below 5.5) with high organic matter content (> 1%) and low salt concentrations (< 2.0 dS/m). These soil characteristics are relatively uncommon in the southeastern United States. Therefore, the blueberry industry has relied on soil amendments to create ideal conditions for blueberry roots. Containers filled with soilless substrates are the latest tool growers have to achieve this purpose.

The soilless substrates used to grow blueberry bushes consist of organic fibers (that provide water holding capacity) and mineral aggregates or organic materials with large particles (that provide adequate porosity and drainage). Coconut coir is a commonly used organic fiber, while perlite or pine bark can be added for porosity. Our research identified several ratios of coconut coir:pine bark:perlite that can be used successfully to grow southern highbush blueberries. Read the full research article.

Growing in containers has strengths and weaknesses. Containers can isolate plant roots from the native soil, helping prevent soil-borne diseases, high pH stress, and nutrient imbalances.  On the other hand, containers constrain the volume of substrate available for root exploration. This renders plants vulnerable to drastic changes in water availability, salt concentrations, and temperature. The ideal container size is one that balances these factors. In our research, we compared 10.7 gal and 13.3 gal containers and found no differences in plant growth and yield. Some farms in Florida and overseas use containers as small at 6.6 gal. Smaller containers might be more economical to fill with substrate, and purchasing prefilled containers can cost less than creating custom mixes on the farm.

With regards to plant nutrition, soilless substrates have two main differences compared to soil: 1) soilless substrates do not contain essential plant nutrients, and 2) soilless substrates have very limited nutrient holding capacity. Therefore, all essential plant nutrients must be provided in the fertigation solution. Additionally, nutrient-to-nutrient ratios in the substrate can be managed very effectively. This has created a need for the development of complete nutrient management recipes for blueberry, (including both macronutrients and micronutrients). Unfortunately, there is very little academic research on this matter to date.

Another area that warrants more research is the farm economics of substrate-based blueberry production. Growing blueberries in soilless substrates can be very costly due to the added expenses of containers and substrates. In our research, we had very high plant density. This allowed us to reach considerable yields in the first two years after planting. While early revenue is certainly welcomed by any blueberry farm, there is a need for enterprise budget and profitability analysis to understand under which conditions this production system can be economically viable.

While the knowledge base is rapidly expanding, there are still several open questions about substrate-based blueberry production. More and longer term experiments will be necessary to develop science-based practices that improve the productivity and sustainability of this new production system.