Using rice hulls in 2018 sponsors ornamental horticulture

Most greenhouse growers use a peat-based substrate for growing their spring crops, however there is a trend towards using alternative substrates such as coconut coir, wood fiber, or parboiled rice hulls. Growers are continually looking to replace perlite in their growing mixes as perlite is a non-renewable, inorganic rock. Some growers are experimenting with using rice hulls in their substrate mixes while others use it to top-dress containers.

First, what are rice hulls? Rice hulls (or rice husks) is the protective covering of rice (Figure 1). The hulls are a by-product of the rice milling industry. Rice hulls can either be fresh or parboiled. Fresh rice hulls are the direct product after milling rice.

Parboiled rice hulls (known as PBH) are steamed thereby killing any seeds
remaining in the product (Figure 2). Whole rice hulls have a pH of 6.5 to 8.0 and are naturally high in silicon which decreases degradation. Similar to perlite, rice hulls increase the drainage and porosity of a substrate without causing significant nitrogen (N) immobilization or tie-up. Ground rice hulls can increase the pH, phosphorous (K) and potassium (K) levels in the substrate. Therefore, growers amending substrate with rice hulls need to be especially careful when using rice hulls as their pH (6.5 to 8.0) is substantially higher than the optimal range for most greenhouse crops, which is 5.8 to 6.2.

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