MASTER GARDENERS COLUMN: Meet the amaranths
What is one of the fastest growing weeds in your garden? At this time of year the corn is just getting knee-high, but who is that poking above the corn? Meet one of the amaranths; also known as pigweed, or specifically red root pigweed.
The amaranths are a rather large family with around 900 relatives. Thankfully, most of them are tropical or subtropical. But they are not all what we label as weeds. One of the striking plants in Cathy's cutting garden this summer is called "Fat Spike," a three-foot or more plant with spikes of purple-red blooms. With one look at the plant you can tell they are related to the common garden weed.
Some of the catalogs that specialize in annual flowers have amaranths that range in color from green to red to orange and purple. One of my favorites is 'Love-Lies-Bleeding,' a plant with drooping blood-red blossoms. How do you suppose it got that name?
In addition to plants grown for foliage or blooms, there are several amaranths that are grown for food. The Aztecs called it huauhtli, and it represented a major part of their cereal grain consumption. Today it is a gluten-free alternative to wheat products with higher protein. A traditional Mexican candy is made with amaranth and honey.
The amaranths we see as weeds in the garden are limited to a few: red root pigweed, tumble pigweed, spiny amaranth, and prostrate pigweed (say that one five times fast). They are so successful due to the number of seeds they produce and how long the seeds stay viable. Each plant of red root pigweed can produce up to 150,000 seeds that stay viable up to 40 years!
As the climate warms and plants are moved on purpose or accidentally, Minnesotans are seeing 'Palmer' amaranth showing up in fields, especially in low-till soybean and other crops. Think of it as pigweed on steroids. It has been a problem for cotton farmers in the south but is now establishing itself much further north. Being a clever weed, it has developed a resistance to glyphosate. Growing up to 10 feet in some cases, it has reduced yields in soybeans up to 70 percent. In southern Minnesota corn fields losses of 90 percent have been reported.
How do you deal with pigweed in the garden? When you till, rake and plant by direct seeding. It is a proven fact that the pigweed seeds that are now at the surface will germinate almost before you put away your rake! Because of this you will be forced to spend some time on your knees weeding until whatever you planted is up to a second leaf stage.
After your seeds are up, a second cultivation is in order and a good layer of mulch will keep light from the soil surface and retard or eliminate most of the weed seed germination. Mulch also helps retain moisture. If you are growing vines of any kind, black plastic mulch can eliminate most of the weeding as well. Do remember that plastic does not let the rain through.
A book I recommend to identify weeds here in the north is "Weeds of the Northern U.S. and Canada" by France Royer and Richard Dickenson. Also helpful is the Minnesota Department of Agriculture website at . Go to the section on Plants/Pests.
More horticultural information can be found on the University of Minnesota Extension website: www.extension.umn.edu/garden/yardgarden/.