Before I broke my leg (I am writing an article about Wheelchair Gardening this week), I regularly took walks in my neighborhood, nearby parks, and nature trails. And what I have noticed is small, gradual changes in the way my neighbors and city workers combat weeds. The move from herbicide applications to alternative weed control methods like mulching and planting competitive native plants is impressive. My outlook on the future of the planet grows and I believe again that we will improve our stewardship of our personal landscapes. Going Green is the tag line used for selling everything from bamboo sheets to the cleaners you use in your home. It is endless … this is my very small part in helping you “Go Green” and have a beautiful landscape.

The Bio-Integral Resource Center in Berkeley, California is committed to improving our weed control (such as noted above) with a new approach referred to as IWM, or Integrated Weed Management. Modeled after IPM (Integrated Pest Management), IWM begins with identifying and monitoring the weed populations in your landscape. Next you determine the thresh hold, or the number of weeds you will allow in your garden. Once you have reached that number, you need to decide the control methods, including cultural, physical, mechanical, or least-toxic chemical controls. This system can be used effectively by homeowners themselves. Professional Landscape Designers can use IWM when planning landscapes to the benefit of the client and the larger environment. 

Design new plantings to keep weeds out

With a new landscape design, IWM practices should focus on weed prevention rather than weed control. A simple way to help your garden is to examine the container and the plant itself when purchasing them to make sure they are weed free. I can give you an example from my own garden a few months ago. In the Sacramento area of California (and I am sure there are many others across the nation) the Sacramento Tree Foundation promotes the planting of trees for greater energy efficiency. Several places in my garden need the benefit of a deciduous tree (shade and cooling of your house in the summer and the warmth of the sun heating your house in the colder months) and I selected a few trees from this organization. In every instance, the soil in the black, plastic containers had not only the beginnings of a wonderful tree, but several types of weeds thriving beside the young tree. By planting these as is, even if I was to pull the weeds, I would have planted not only Birch and Redbud trees but all the weeds that came with them. Instead, I soaked the trees well before planting, and pulled out the weeds and any easily removed roots. Further, I made certain that the topsoil I was using had been properly composted at 140 – 150 degrees.  Composting at a high heat ensures that weed seeds have been killed. A little extra effort = less or no weeds from these plantings.

Suiting your plants to the cultural conditions, allows for plants that will flourish, and weeds will have no place to grow. Native plants are especially useful because they are generally well adapted to local conditions, and they complete well against weeds. You ca also use groundcovers, trees, and shrubs to shade the ground so weeds will not grow beneath them. Underplant newly planted trees and shrubs with  fast growing annuals like sweet alyssum (Lobularia maritima) and flaxes (Linum spp.) to crowd out weeds. In climates where plants depend on watering, use drip irrigation to deliver water only to your ornamentals and not to the weeds. Give allelopathic plants, like sunflowers, manzanita, and some sages, which secrete toxins that can suppress the growth of other plants (Fine Gardening: Say Good-by to Weed Worries).

Photos below and to the left represent some of the flaxes used in weed regulated gardens.

Synthetic mulches are also effective tools for suppressing weeds. The best time to install plastic mulches or landscape fabrics is when you are installing a new bed. I personally stay away from the black plastic sheeting (polyethylene) but I do like spunbound, woven, or nonwoven landscape fabrics (polypropylene or polyester). I have been told that the black plastic suppresses weeds better, but the landscape fabrics last longer, allow water to drain through, and are sold in sheets of convenient sizes that I find easier to use. In fact, some fabrics are pre-cut into “tree circles” that provide a circular weed-free area beneath trees. All these synthetic mulches are degraded by sunlight and should be covered with a 2-inch layer of organic mulch (bark of your choice – with the exception of black bark which leaches into the soil and water table) or some sand or gravel, to protect them. Installed correctly they can last from 5 to 10 years;  sometimes even longer.

In most cases I have found great success using organic mulches and I encourage my clients and readers to use these mulches, too.If only in the beginning of your own person IWM program, there are a great variety of mulches available to you. Coarse mulches, like large bark chips, should be used in areas of high rainfall, because they allow water to drain quickly. Water that sits with a mulch is a breeding ground for disease. Deep mulches are more effective in controlling weeds than shallow ones. Most people apply less than what is necessary to give the best coverage and weed control. As a rule, organic mulches should be 2 to 4 inches deep, and they should not come in direct contact with the trunks of trees or the crowns of plants.

Note: There is more information regarding organic bark in the article titled “Mulches in the Landscape”.

Creating a Weed Map … Identify problem areas

I am very thankful to Kim Jaeckel for the illustration below. It is inserted into this article to give the reader a visual of a weed map. If you are working with a Landscape Designer, ask them for a copy any base plan, site plan, blue print, etc. that reflects your property, with an accurate scale (usually 1/8″ = 1 foot, 1/4″ = 1 foot, or from the builders original plans, 1″ = 10 feet). If you are not working with a designer, you can look through your paperwork saved with the purchase of your home, any home improvement/addition that you had a plan drawn for, or you can simply measure your property itself. Best to have your home place accurately within the larger landscape, the perimeters of your home, any hardscapes, and any significant trees or plantings. From that you can begin identifying your weeds on the way to determining your tolerance for weeds.

Once your new or renovated landscape is installed, or when you inherit a landscape, you will begin to monitor for weeds and set wee tolerance thresholds. With your weed map in hand, you will move through your garden identifying areas with weeds. Your tolerance for these weeds will determine to what degree you will, using IWM principals, you can live harmoniously with the weeds in your garden.

Map your garden and observing where and to what intensity your weed or weeds are growing, begin to identify the types of weeds that you have. Not long ago, I did my very best to rid our side yard of all the weeds and the little bit of grass that remained. My plan was to prep the soil, bring in the amendments, and install the landscape I had developed per plan. As the weeds and grass continued to die off, my husband grew more upset. To him it was better to have an area full of green weeds and some grass than nothing at all. Well I certainly agreed, but I had a plan and it would be fulfilled.

Fall came and with it one of the best times for planting. At least the trees. At least the prep of the soil and maybe just a seeding rather than sod. You know where this is going ….. no prep, no sod, no trees, no landscape. We had a lot of rain this year and between the rain, the mud, a new puppy ….. just life …. we just mowed down all the weeds and hope to at least improve the area.

Most important … in terms of IWM, we know our tolerance threshold  and have identified ALL the weeds. Some will come back, and we have decided they are o.k. The others … well we will deal with them. We have decided that some of our weeds are aesthetically pleasing an non aggressive growers, so we will tolerate them at certain numbers. Other weeds may be useful herbs or can be a refuge for beneficial insects, since they provide them with pollen, nectar, prey, or r alternate hosts. But beware; some weeds like sedges (Cyperus spp.) or Canaa thistle (Cirsium arvense), should be removed at once or they may quickly take over your garden.

A map like the one below will help you determine the places in your garden that will take your energies and will need attention.  For example, an area overrun with annual weeds like shepherd’s purse (Capsella bursa-pastoris) and common chickweed (Stellaria media) should be treated before they can set seeds. Perennial weeds, like ground ivy (Glechoma hederacea), are weakest about two weeks after emergence, when food stored in the roots has been exhausted, so this is a good time to treat them.

A Landscape Designer’s plan, prior to final concepts, is great to use as your weed map as well. The drainage, soil conditions, acidity level and fertility of the soil may (depending on the designer and how detailed they are) be on your site plan or one of the first drawings your designer draws for you. Certain weeds will flourish under certain cultural conditions, so the presence, or health of a specific weed will give you clues about the general health of your soil.   If you see the presence of spurge (Euphorbia spp.), black medic (Medicago lupulina) or crabgrasses (Digitaria spp.) can mean that the site is too dry and most likely significantly compacted. Moneyworts (Lysimachia spp.) and nimbiewill (Muhlenbergia screber) are indicators of chronically wet conditions. Broadleaf plaintain (Plantago major) and goosegrass (Eleusine indica) also inicate compacted soil. Red sorrel (Rumex acetosella) shows up in acidic soil, and sites low in nitrogen lead to clovers (Trifolium repens), bird’s-foot trefoil (Lotus corniculatus), and black medic. When signature weeds appear on your map, yu ca try to get rid of them by aerating or cultivating, working compost into your soil and bring slow-release fertilizer into the soil. If acidic soil is your issue, you can treat it with lime.

This is the first of several articles coming to our readers regarding Integrated Web Management and Organic Gardening. Next we will cover the tools that will best serve you in dealing with weeds. I hope you come back .. soon!