Container Type but not Substrate or Hydrogel affects Establishment of Sandhill Milkweed (Asclepias humistrata)

Abstract

Coastal dunes are threatened by climate change and development and need restoration. Diversity of dune restoration plantings is often limited as planting protocols are lacking for coastal dune species. We studied the effects of production container, substrate type, and hydrogel application at planting on transplant survival of Asclepias humistrata (sandhill milkweed), a critical species for Danaus plexippus (eastern monarch butterfly) conservation. When planted within coastal backdunes in late-spring/early-summer, survival did not differ among plants grown in four substrate types: an industry standard mix with perlite composed of 75% pine bark to 25% Metro-Mix 830 or one of three perlite-free mixes including 70% coco coir to 30% HydraFiber, 70% peat moss to 30% HydraFiber, or Sunshine Mix PF. Plants grown in tall tree tubes with a deep soil profile had higher survival (81–76%) than plants grown in an industry standard tray of 32-cell liners (33–32%) 36 to 91 days after planting (DAP). Survival was also highest for tall tree tubes post hurricane Sallie (334 DAP). Application of hydrogel during spring planting of containerized A. humistrata did not improve survival. Survival decreased from 80% to 69% between 100 and 167 DAP and was 48% post Sallie (410 DAP). Neither substrate, container type or hydrogel effected plant height or width. Asclepias humistrata can be successfully planted with an acceptable survival of 70% at 100 DAP when grown in tall tree tubes or containers with a deep soil profile using various perlite-free substrates and without the need for hydrogel application at planting.