GARDENING: Getting the upper hand on weeds |

GARDENING: Getting the upper hand on weeds

Curt Swift
Free Press Gardening Columnist
Courtesy / Curt Swift
Staff Photo |

Weeds always get ahead of me. This year redroot pigweed is my nemesis. This fast-growing annual is very easy to pull as long as the soil is wet. The roots of this and most other annual weeds are quite shallow without the underground rhizomes and deep roots of perennial weeds.

The typical recommendation is to keep weed growth under control. Weeds compete for water, nutrients, and sunlight with the plants we are trying to grow. When I finally attacked the pigweed in my lavender cutting garden, it was obvious these weeds were shading the soil and helping keep it moist. In this regard the weeds were beneficial. These weeds were also shading my young plants protecting them from the brutal hot sun. Even with the benefits provided by these weeds, I decided to pull them. Now that they have been pulled, the lavender will have greater access to nutrients.

Instead of throwing the weeds in a compost pile, I left them between the rows of lavender to serve as mulch. The mulch will provide the same benefit of shading the soil and reducing water loss. This layer of dead plants will also help increase the organic matter content of the soil and nutrients as they decompose. The worms will love this addition of organic matter and aerate the soil-improving oxygen and water movement into and through the soil. Even if I didn’t already have worms in this garden, by adding organic matter worms would have shown up from somewhere. They always do when you improve the organic content of your soil.

Most garden writers recommend spacing plants so close little or no soil is exposed to the drying effects of the sun. Most people can’t afford the number of plants required to plant this close and consequently depend on mulch to do the same job. You might find some of the lavender growers in the area use bark mulch to shade the soil throughout their fields. Those who use mulch find their plants survive the winter much better than growers who do not cover the ground with mulch; an added benefit.

Lavender without a mulch cover tends to break dormancy sooner than lavender where the soil is covered with mulch. When plants break dormancy too early in the spring, they are more susceptible to spring frost; mulch helps prevent this damage. All perennial gardens should be covered with a protective layer of mulch.

Some gardeners use weed barrier to keep weeds under control in their gardens and around their trees. If the fabric is dark and not covered with an organic mulch like wood chips or bark mulch it will absorb heat and increase the tendency for perennials to break dormancy earlier than if the fabric had a mulch cover. Black fabric, like dark soil, heats up and re-radiates that heat to the plant. Black landscape fabric also causes heat build-up of the air underneath the fabric. This heated air escapes through the holes you made to plant your flowers, vegetables and perennials. As the heat escapes it cooks the stem, damaging or killing the plant. A layer of mulch over the fabric helps prevent these heat-related problems.

As the mulch in my lavender cutting garden decomposes, the microbes responsible will need nitrogen especially since I’ll be adding wood chips to the mix of dead weeds. This layer of green weeds and wood chips will act as a compost pile without the heat build-up. In this case, the compost will be in a sheet covering the soil and, for obvious reasons, is called “sheet composting,” The green tissue of the weeds will provide some nitrogen but not enough so I’ll scatter a small amount of nitrogen over the garden to take care of that need. Even if I wasn’t going to sheet compost I would still add nitrogen.

Lavender, like other perennial crops, needs nitrogen to develop new tissue to help strengthen the plant and increase its chances for survival. Research from different areas around the world report one-half pound of actual nitrogen per acre applied after the first harvest improves plant health. Some cultivars of lavender bloom twice, with the second bloom appearing in autumn. Fertilizing after the second harvest can increase winter injury and needs to be avoided. These fertilizer guidelines hold true for most perennials so don’t be afraid to apply a small amount of nitrogen in mid to late summer around your perennials. Just don’t apply too much and always water the fertilizer in.

If you are interested in learning more about lavender, join me and other lavender growers at the Lavender Festival July 12-14 in Palisade’s Town Park. If you are interested in classes on how to grow lavender and the use of lavender in aromatherapy, massage and even cooking, you should plan on attending some the Saturday classes.

Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at, 970-778-7866 or check out his blog at He owns Swift Horticultural Consulting and High Altitude Lavender.

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