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Milking milkweeds for more monarch butterfly habitat

Date: August 19, 2019

Milkweed plants grown to produce seeds for restoration work can have their taproots harvested and used for restoration too, thus getting more restoration benefits from the same plants


Background

A Monarch Butterfly
Milkweed plants are an important host species for both monarch larvae and adult butterflies. Photo by Tom Koerner, US Fish & Wildlife Service.
The rapid demise of monarch butterflies, whose larvae feed exclusively on milkweeds, is a serious concern to Canada, Mexico, and the US. It is believed that loss of habitat (milkweeds to feed upon) is one main reason for the dramatic decrease in the monarch population. Thus, increasing the amount of milkweeds that can be produced to restore monarch habitat hinges on the ability to more efficiently produce more seeds and plants.

Research

Milkweeds grown in “seed increase beds” in nurseries provide large amounts of genetically appropriate seeds for specific projects. Once these projects are completed, the beds are often decommissioned and the plants are discarded. Milkweeds, however, have persistent, woody taproots that produce new shoots when plants are disturbed. Researchers wondered if these roots could be harvested, stored, and used in restoration projects, thereby maximizing the investment made in seed increase beds.

Researchers harvested taproots from a three-year-old seed increase bed and stored the taproots several ways during the winter. The following spring taproots were outplanted and evaluated for survival and growth.

Key Findings

Taproots can readily be stored in cardboard boxes placed in either cooler (33–36 °F) or freezer (23–28 °F) conditions, and that subsequent survival increases with the addition of protection from the cold in the form of plastic bag liners and (or) peat moss; survival was as high as 90 percent.

By utilizing cold storage, milkweed taproots can be harvested, stored, and outplanted at the proper time to produce viable and prolific plants for further restoration work and monarch habitat rehabilitation.

Harvesting the taproots is an effective way to efficiently use all parts of the increase bed.

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Principal Investigators: 
Principal Investigators - External: 
Melissa Topping - University of Idaho
Forest Service Partners: 
John Justin, J. Herbert Stone Nursery, Region 6, Central Point, Oregon
External Partners: 
Thomas D Landis, Native Plant Consulting, Medford, Oregon
Douglas Kendig, DOI Bureau of Land Management
Research Location: 
: J. Herbert Stone Nursery, Central Point, OR and Moscow Forestry Sciences Lab, ID