A reader asked me, “What is Annual Bluegrass and how do I control it in my lawn?” Annual Bluegrass (Poa annua) is a cool season, winter annual. It is a light green, bunch-type grass that grows low, and is capable of producing seed heads at mowing heights lower than ¼ inch. If your lawn turns white from seedheads in June , you might have an older Kentucky Bluegrass variety or blend but probably have Annual Bluegrass as Kentucky Bluegrass rarely seeds prolifically in Nebraska . Kentucky Bluegrass for seed is grown in parts of the country that have longer growth seasons, and cooler and less extreme summer temperatures.

          Many yards, including Fescue lawns, have Annual Bluegrass but the caretakers don’t know it. Annual Bluegrass looks great and full in the spring then goes to seed. It often dies suddenly in the hot summer of July and early August, and you may think you have grubs or a disease. The seed then germinates in August and the lawn looks great again in September and growth often continues through the winter.

          Before treating your lawn for any weed or disease or insect problem, make sure you get an informed and accurate diagnosis!!! Annual Bluegrass is hard to identify unless you have a microscope or a strong magnifying glass to examine the structure of the grass, and you know what you are looking for, or you see the grass when it goes to seed. If your lawn goes to seed next June, take a 6 inch or 8 inch square piece of sod that has gone to seed to your local County Extension office or to a full service garden center that has someone who knows how to identify the type (or types) of grass you have. After identification they will give you back your piece of sod so you don’t have a big hole. Even Fescue lawns can have Annual Bluegrass, especially if you started with sod. 

          Earlier this season I wrote about other “Winter Annuals” such as chickweed, henbit, and pennycress and how to control them. I wrote that winter annuals are plants that germinate in the fall, survive our cold winters, continue to grow in the spring and produce seeds, then die in the summer when the temperatures get very warm. There are also winter perennials like dandelions and ground ivy that germinate in the fall, over winter, and then go to seed in the spring. Unfortunately they are perennials so don’t die over the winter. While it is technically classified as a winter annual, Annual Bluegrass sometimes survives as a short lived perennial, and unlike most cool season grasses can produce seedheads anytime it is actively growing.

          Strategies to control Annual Bluegrass differ from control of winter annuals and winter perennials.  Culturally Annual Bluegrass can be suppressed by raising your mowing height, reducing fertilizer applications, and cutting back on irrigation in the fall to minimize germination. Chemically there are two ways to control Annual Bluegrass. The first is to put on a pre-emergence herbicide around August 1st, but no later than August 15th, and the second method, and most reliable, is to spray it in the late fall (late September) or in the spring, with glyphosate (Kleen-up or Round-up). This will of course kill the surrounding desirable grass. Trimec, Triclopyr, Weed-Be-Gone, Brush Killer, and other “weed herbicides” will not kill Annual Bluegrass.  Regardless of how you get rid of it, you will have to re-seed that area if you have a large patch. Buy good grass bred for our Midwest climate. Your lawn will never look any better that the quality of grass you plant.

          Thanks to Dr. Roch E. Gaussoin , Professor and Extension Turf Specialist at the University of Nebraska-Lincoln for reviewing and editing this article.  

Copyright 2009







          The common myth is that we mulch our plants in the fall to keep the ground warm. The truth is we mulch in late fall to keep the ground cold. More winter hardy plants are killed by the freezing and thawing than from the cold. So we want to put the mulch on the soil after a couple hard freezes and then keep the soil cold. I usually do not cover my roses until after Halloween and sometimes as late as Thanksgiving. Gardeners who put their mulch on too early in the fall keep the ground too warm, and then when we get a sudden freeze, the plant is not ready and winter kills. In the fall allow the ground to cool down normally so the plant goes into dormancy as it should, then put on your winter mulch.

          Remember the warm spells we had last spring and then the cold spells, and then the warm spells, and then the cold spells? Plants that were not properly mulched or had their winter mulch removed too early, warmed up and some broke dormancy. Then when we got the cold spell they could not go back into dormancy and froze. In northern climates such as North Dakota , Montana , and Minnesota where it snows and the snow stays all winter, some plants do better because the snow insulates the ground and keeps the soil from thawing out too early in the spring. 

          What is the best mulch? Each gardener has his or her favorite. Gladys uses lots of compost from her huge compost pile. I use wood chips or shredded hard wood on my roses, shrubs, and other perennials because I have access to it. I use compost on my peonies, raspberries, asparagus, and rhubarb. Some gardeners use shredded leaves and grass. Do not use leaves that have not been shredded by a grinder or your mower, or grass that has not dried out for a couple days. These tend to mat down rather than have air spaces which helps insulate.

          Do not use those foam cones unless you cut the top out. Then fill the inside with mulch, compost, or soil. On a warm winter day the heat builds up inside a cone that has the top still on it. This heat builds up and heats up the soil, causing the plant to break dormancy. With the next hard freeze the plant then freezes and dies. They are easy and convenient to use, but they do not work.

          Remember, mulch in the winter to keep the ground cold, and mulch in the summer to keep the roots cool and the ground from drying out.

Copyright 2009