“Weeds, weeds, inglorious weeds! We pull you. We dig you. We spray you, yet there you doth remain.” As this little known quote from some unknown 17th century writer says, we spend a lot of time battling weeds in our gardens but the war seems never won. In this last installment of my series on managing pests in our gardens, weeds are the focus. Like all garden pests, the more you know about them, the more successful you will be in keeping them at bay.
By any other name
What makes a plant a weed depends on your perspective. To the lepidopterist, the flowers of Asclepias syriaca or common Milkweed is an important food source for many butterflies including the Monarch. Its rhizomatous nature, however, is problematic for farmers because it can quickly colonize large areas crowding out any other plants.
Sometimes it comes down to location. Poa pratensis, better known as Kentucky bluegrass, is readily accepted in our lawns, but once its stolons cross our bed lines, we are very quick to bring out the edger to keep it from creeping into our beds.
Even pretty flowers doesn’t exempt a plant from weed status. Glechoma hederacea suffers from that fate. Also known as ground ivy or creeping charlie, it has lovely flowers but is regarded by most as a heinous weed of both lawns and gardens.
Weeds are basically plants whose nature and habits make it obnoxious, plants only a mother could love. They can come from other countries like garlic mustard, supposedly transported by settlers moving west for its garlic flavoring potential. Weeds can also be native like the common milkweed mentioned above. They have a high reproductive potential and an ability to adapt to all kinds of environmental conditions. Most of all, they conflict with our needs and desires, leading to the endless battle between us and them.
The name game
Like insects and diseases, the more we know of our weeds the better equipped we are to combat them. Weeds come in all types. There are annual and perennial ones. They can be further classified into annual grassy weeds and annual broadleaf weeds, and even further with the winter annual grassy weeds and the summer annual grassy weeds.
It is not as confusing as it may sound, and if you know the difference between a perennial or annual in your garden, you’re already there in the basic classifications of weeds. Most weeds in our gardens are one or the other, though there may be a few that are biennials, plants that grow two years and then die after setting seed.
Then there are the broadleafs and grasses. The terms pretty much explain themselves and are most often used to describe the targets of selective weed killers or herbicides. Broadleaf herbicides, for example, will not kill grasses. They are most often used in lawns to kill broadleaf weeds such as dandelion, plantain, or ground ivy without killing the grass.
It is also helpful to know whether a weed is a winter annual or summer annual. Winter annuals such as hairy bitter cress germinate in late fall. Like winter wheat they overwinter as plants, and then finish their growth in early spring. They are often already setting seed by the time we can get out in the garden in the spring. Summer annuals like purslane and crabgrass prefer the opposite. Since annual weeds regenerate themselves each year from seed, control most often centers on disturbing the germination of the seed with what are known as pre-emergent herbicides. Once again, timing is everything and differs whether controlling winter or summer annuals.
The root of it all
The oldest method of weed control is the hoe. It can be very effective, but it is labor intensive and needs to be repeatedly done, particularly if there are perennial weeds present whose roots run deeper than most hoes cultivate. Annual weeds are the most easily controlled by this method because their roots are most often shallow. It also helps to cultivate before they set seed, otherwise, they will return.
Mulching after cultivating can help the reemergence of annual weeds from seed because most seed needs some light to germinate. Pre-emergent chemicals such as Preen can also be applied to squelch any newcomers. Pre-emergents are specific to the control of certain weeds, and if you have plans for planting anything in the area, you may have to wait a certain period of time. That is why it is important to READ THE LABEL.
Mulch can also be used to smother perennial weeds if applied thick enough. Chuck Gleaves, Director of Kingwood Center, uses this method to create new planting areas. Using rough mulch from tree chippings he dumps a layer one to two feet deep over the planting area. Even the most robust perennial weeds seem to exhaust themselves trying to penetrate it. It is essentially the same principle as using cardboard, landscape fabric, or black plastic. The difference is that after a couple years of the mulch decomposing, you have a very rich planting bed.
Chemical control is sometimes necessary, but it is important to know the different types of herbicides in order to use them safely and most effectively. Herbicides can either be selective or non-selective. Broadleaf herbicides, as mentioned above, can control weeds in your lawn without killing the grass. That is a selective herbicide.
Roundup is a non-selective herbicide. It kills anything green. Using it in your lawn to kill dandelions will also kill the grass. Roundup is also a brand name. The active ingredient is glyphosphate. When comparing herbicides it is important to look at the active ingredients required by law to be listed on the label. There are generics of Roundup out there that can save you money.
The advantage to using the brand name are the surfactants that are added to help it stick to leaf surfaces and make it rainfast. These can often be bought and added to the generics. Like any chemical there are potential hazards to their use. READ THE LABEL.
Herbicides are also categorized as either pre-emergent or post-emergent. Pre-emergents are most often used to control annual weeds such as crabgrass. They form a vapor barrier that kills emerging seedlings. That is why timing is important. If the barrier is not in place when the seed begins to germinate, it won’t work. The deadline for crabgrass is said to be when the forsythia is in flower.
Environmental conditions are also key to the success of a pre-emergent. Some require moisture to be activated. The label will tell you. READ THE LABEL.
Pre-emergents will not kill existing weeds. For that, a post-emergent such as Roundup is needed.
Highly concentrated vinegar and salt solutions can act as herbicides. More and more they are appearing on store shelves. A 20 percent concentrated solution of vinegar is said to be the most effective. The vinegar in our kitchen cabinet is usually only about 5 percent. They do a good job of killing the top portion of a weed which will kill annual weeds; however, repeated applications may be needed to control perennial weeds.
The increased availability of these safer herbicides are in response to concerns over the lasting effect of not only herbicides, but all pesticides on our environment. That is why it is important to use them in a measured and responsible way. The principles and strategies I have written about over the past few weeks are a way of doing that.
When faced with a pest problem remember to identify the culprit before reaching for the spray bottle. Then determine if you can live with it. If not, try the least toxic method first. Aphids and spider mites can often be controlled by repeated spraying with water. If chemical control is needed, READ THE LABEL completely to make sure it will take care of the problem, and how it should be applied. The importance of reading the label cannot be emphasized enough.
Also remember that timing is everything and educate yourself. One of the best sources for information on pests in our gardens is the weekly Buckeye Yard & Garden Line (BYGL) newsletter. It is the summary of a weekly conference call between The Ohio State University (OSU) extension agents around the state about what’s happening garden-wise in their areas. It can be found at www.bygl.osu.edu.
If you need to contact me with a question or a garden inspired event, jmakley@centurylink.net is the way.
Since his days as forced labor in his mother’s garden, John has learned to enjoy gardening and has actually made a career out of it. From the backyards of Columbus to the rooftops of Manhattan, John has soiled his hands. Former Head Gardener at Kingwood Center, John still gets his hands dirty in the local community. You can contact him at jmakley@centurylink.net.