Defeat Your Weeds

dandilion-boulderco-3may07-lah-048With the weather swinging wildly between winter storms and balmy sunny days, it must be springtime in the Rockies. The snow reminds us that it’s much too early to plant, but the warm days in between beckon us outside. What’s an antsy gardener to do? Happily, there are things you can do to prepare for the gardening season. Unhappily, one of the most important chores is weed control.

Daffodils and tulips are sending up leaves, perennials have tiny, tentative shoots, grass has a green tinge—and weeds are exploding out of the ground. This is the time to gain the upper hand.

Not only are weeds an eyesore, but they compete with the rest of your plants for water and nutrients—and even sunlight, if they get too large. Specially adapted to grow where the soil has been disturbed, weeds will win the battle every time, unless the gardener takes action.

In general, the first weeds to emerge are perennials, who have a root full of stockpiled carbohydrates to support their early growth. While I love their bright yellow flowers—often the first color in my garden— dandelions thrive in the cool soils of early spring. So does black medic (Medicago lupulina), with its clover-like leaves and tiny yellow flowers.

Perennial weeds are difficult to control. Most have a substantial tap root, which breaks off when you attempt to pull up the plant. From that remnant, it stubbornly sends up shoot after shoot. You can keep removing the top growth until the plant runs out of food and gives up, but it may take all season… or longer. This technique is called “frustrating” the weeds, but it’s usually the gardener who gets frustrated!

winter-beds-home-lah-7Another option is to cover the weeds with a thick layer of mulch, adding more as the green leaves break the surface. If you can’t effectively smother the weeds, at least the ground underneath will be softer, making it easier to dig out the roots.

A faster solution is to spray a systemic herbicide such as glyphosate. This broad-spectrum chemical (initially marketed as Roundup or Kleenup, now widely available as a variety of brands) is absorbed by the leaves, transferred to the root, and will kill the plant in one to two weeks. The most resilient noxious weeds may take repeated applications before they succumb. However, like all chemicals, glyphosate can have unintended effects. Caution should be used to avoid breathing the spray, or getting it on either yourself or other plants and animals. Carefully follow the directions on the package, avoid spraying if there’s any wind, and wear protective clothing. (To limit the amount of herbicide you introduce to the environment, you can use a paint brush to apply it solely to the leaves of the plants you intend to killing.) Glyphosate breaks down fairly rapidly, and you can plant two weeks after applying it.

(I should note here that spraying broad-spectrum herbicides in a lawn will also kill the grass. If you wish to use a chemical weed control in a lawn, use a broad-leaf weed killer such as the 2,4-D combinations found in “weed and feed” type products.)

Non-toxic sprays, such as vinegar and boiling water, will kill the top growth, but you still have the root to contend with (see “frustrating” above). Large amounts of salt will kill most plants, but it remains in the soil indefinitely. Only use salt where you want permanent control, such as in patio cracks. And remember, rain can wash it into the surrounding garden areas where it will create a dead zone.

boulderco-3may07-lah-051As the weather warms, weed seeds will also be germinating. Many of these seeds need light to germinate. We can use this fact this to our advantage. Amending and turning over the soil will bring a new crop of seeds to the surface, where they readily sprout. As soon as they do—kill them! In this case, the non-toxic sprays work just fine, since the plants haven’t had a chance to get established. If you hoe, pick a dry, sunny, windy day, and the baby weeds will wither right before your very eyes. Or you can smother them with a nice layer of mulch or landscape fabric.

Pre-emergent herbicides prevent new weeds from sprouting in the first place. This can be a huge help in established plantings, where digging or spraying is difficult. A number of types are available (including some organic options), and they work in slightly different ways. It’s best to see what products are available locally, and carefully read the package directions to see if a product is appropriate under your conditions. If you intend to use pre-emergents, apply them as soon as possible. They need to be in place before the seeds start to germinate.

No matter how you go about it, eliminating as many weeds as possible early in the season makes life easier for both the garden and the gardener.

For more detailed information on weed identification and control, visit the CSU extension website.

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