Effect of overwintering method on winter survival of garlic mustard (Alliaria petiolata) rosettes grown in containers

Abstract

The objective of this study was to develop reliable methods to increase the winter survival of rosettes of the biennial species, garlic mustard, when overwintered in containers in Minnesota. To develop these protocols, we borrowed techniques perfected in the nursery trade to overwinter perennials with methods that did not require specialized structures, such as unheated poly-houses. Rosettes growing in containers overwintered successfully in a pot-in pot-system, straw sandwich method and when mulched in a raised bed over three successive winters when well-watered prior to addition of mulch. Levels of rosette survival ranged from 70% to 100%. Containers placed on landscape cloth and left uncovered did not survive the winter. The overwintering treatments moderated the fluctuation of soil temperature at the crown level in garlic mustard rosettes with soil temperatures hovering around 0 C. Rosettes growing in-ground in a wooded area averaged 83% winter survival. The ability to successfully and predictably overwinter garlic mustard rosettes will be beneficial for rearing the biocontrol agents, Ceutorhynchus scrobicollis and Ceutorhynchus constrictus.