Roots, Shoots, Fruits & Flowers: Hügelkultur Gardening & White Grubs

If you want to experiment with a new technique, then this edition of RSFF will help you. The next few paragraphs will share a new horticultural concept.

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Cross-sections of a hügelkultur bed. The difference is the thickness of the layer of stems and branches.
Photo: Washington State University Extension.

New gardening method called “hügelkultur”

Peggy was exploring a new gardening method called “hügelkultur” and sent this email, “We have a sloped area in our yard and have looked into adding some hügelkultur beds there. Do you have any knowledge of these beds? In our research the main downside we have found is that termites are attracted to the decaying wood. We are interested in placing fruit trees in this area. Any guidance you can give will be appreciated.”

The extension services from Texas, Washington and Wisconsin shared some information about this gardening technique on their websites. The Master Gardeners of Wisconsin has an understandable, practical narrative about hügelkultur and wrote, “Hügelkultur translates to “mound culture” and has been used for some time in Eastern Europe and Germany.

To create a hügelkultur bed, either make a depression in the earth, or simply pile material on top of the soil, making a bed that is six feet long and three feet wide. Begin with a layer of larger logs, avoiding cedar or walnut, because both produce biochemicals that detrimentally influence seed germination. Next, add a second layer made up of smaller branches, followed by filling all the crevices with leaves, organic material, kitchen scraps, etc. Water each layer well as the mound is built; finish it off by adding several inches of soil to the top and sides. When complete, the mound should stand roughly three feet tall.

The mound must rest for several months as it decomposes and settles into something more appropriate for a garden bed. In our more northerly climate, it will take more than a few months of decomposition for the bed to be ready for planting, so plan on a minimum of 12 months. However, if you use partially rotted wood in the initial build, the decomposition process will occur more quickly.

There are some drawbacks to this method. Weeds are a significant problem and flourish rapidly on the surface of the mound. Also, the mounds will also collapse over time. In the original German publication, the authors indicate that the beds have a lifespan of only 5–6 years and must be rebuilt from scratch. Therefore, it would be unwise to plant any type of tree or perennial bed such as asparagus, strawberries, or other fruit in a hügelkultur bed.”

CAUTION: The concern about termites is valid so the hügelkultur bed should be located away from homes and other wooden structures. This method is to be especially avoided in foundation flower beds of a home.

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A closeup of two small grubs, probably the brood of June beetles, in the palm of a rubber glove.
Photo: Paige LeBeau.

White grubs

Paige wrote, “In cleaning up a high rise [container] bed, I kept exposing numerous white grubs. What insect do they morph into and how to get rid of them? Of course, I removed those I dug up and promptly got rid of them. But they’ll be back if I don’t take care of the problem.”

An insect specialist at the Louisiana State Arthropod Museum examined the image and responded, “I think it is one of the Phylophaga species. usually May or June Beetles. but this year there seems to be a lot of March beetles!! “

Paige then wrote after the identification, “I was thinking they might be good for fishing.” Yes, using them as fish bait for bream and other panfish would be a good control measure.

Clemson University shares this biological treatment for white grubs in the lawn, “Milky spore disease is a soil inhabiting bacterium (Paenibacillus popilliae) that is ingested by the grub during normal feeding. The bacterium then kills the grub and upon desiccation, the grub will release more bacterial spores into the soil. Milky spore disease is nontoxic to non-target species in the lawn. As with all biological controls, efficacy can be highly variable depending on the site and the environmental conditions at that site.”

An online search of “milky spore” reveals the ready availability of products for homeowners and gardeners to purchase and to control these lawn grubs. The residual benefit of this safe, biological treatment would last for years.

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or khawkins@agcenter.lsu.edu. Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

4/13/2020 1:06:40 PM
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