Effect of Substrate Stratification on Growth of Common Nursery Weed Species and Container-grown Ornamental Species.

Substrate stratification is a method of filling nursery containers with "layers" of different substrates, or different textures of the same substrate. Recently, it has been proposed as ameans to improve drainage, substratemoisture dynamics, and optimize nutrient use efficiency. Substrates layered with larger particle bark as the top portion and smaller particle bark as the bottomportion of the container profile would theoretically result in a substrate that dries quickly on the surface, thereby reducing weed germination, but thatwould also retain adequatemoisture for crop growth. The objective of this studywas to evaluate the effect of stratified substrates on the growth of common nurseryweeds and ornamental crops. This study evaluated the use of coarser bark (<0.5 or 0.75 inches) as the top substrate and finer bark (<0.38 inches) as the bottomsubstrate with the goal of reducing the water-holding capacity in the top 2 to 3 inches of the substrate to reduce weed germination and growth. Results showed that substrate stratificationwithmore coarse bark on the top decreased the growth of bittercress (Cardamine flexuosa) by 80% to 97%, whereas liverwort (Marchantia polymorpha) coverage was reduced by 95% to 99%. Substrate stratification initially reduced the growth of ligustrum (Ligustrumjaponicum) and blue plumbago (Plumbago auriculata), but there was no difference in the shoot or root dryweights of either species in comparisonwith those of nonstratified industry standard substrates at the end of 24weeks. The data suggest substrate stratification could be used as an effective weedmanagement strategy for container nursery production. [ABSTRACT FROM AUTHOR]