Organic Gardening: Reading the weeds

With the warming days and rainy weather, most of us are seeing an explosion of weeds in the garden along with the plants that we intended to put there. Pulling or otherwise suppressing weeds is one of the great struggles of gardening, but this article is intended to hit the pause button on that impulse and ask what it is the gardener can learn from these often-unloved plants.

              A common definition for a weed is “a plant that is out of place”. This elegantly expresses the fact that many plants that arrive uninvited are simply ornamentals or crop plants that grow a little bit too-well where we don’t want them too. And yet, it also supposes that these plants should be elsewhere when, in many respects, weeds are exactly where they should be.

              Sometimes referred too under the more generous title of “spontaneous vegetation”, weeds often thrive in and colonize spaces that have been disturbed. They help cover and improve soil, serving as pioneer species that loosen and enrich the ground for others. Most of our gardens are in a state of disruption, with ground being cultivated, disturbed or left bare, creating conditions where these plants can thrive. By observing the types of weeds that occupy these areas, the gardener can learn a bit about the state of her soil such as its fertility, structure and moisture level.

              A great source for information on this topic and other soil issues is The Soul of Soil by Grace Gershuny and Joe Smillie. The authors stress that “a few individual weeds don’t mean much”, but a preponderance of them–especially perennial ones–often point to specific growing conditions. For help identifying weeds at various stages of growth, Weeds of the Northeast by Richard H. Uva, Joseph C. Neal and Joseph M. DiTomaso is an excellent source of information. 

              An example of weeds that can help inform the grower are chickweed, lamb’s quarters and red-rooted pigweed. These generally grow in fertile, cultivated soils, unless they are small and stunted, which suggest the earth is not as healthy as it could be. Interestingly, these are all edible plants that seem to be right at home among other food crops, even if we wish they weren’t.

              Chickory and dandelions point to compaction and heavy clay. And, although digging up dandelions from the lawn is a favorite pastime, the plant’s taproot helps break up and improve compacted ground, indicating it might be better left in place. Indeed, many weeds offer free soil improvement services.  As Gershuney and Smillie say, “Perennial weeds in particular are frequently deep rooted, helping break up hardpans, aerate the subsoil and bring up mineral nutrients from areas too deep for crop roots.” Other plants, such as clovers, fix nitrogen and enrich the soil.

              A cursory glance at the spontaneous vegetation in a patch of ground can also say a lot about the moisture level. Docks, beggarticks and yellow nutsedge like wet growing conditions, whereas purslane, thistle and mullein prefer dry soil.

              Of course, weeds are also important to pollinators and other wildlife. Many of us know that various types of milkweed are critical for monarch butterflies. But other plants like clover, dandelion and dead nettles can be important for honeybees and other pollinators. Keeping some of these around can be important for encouraging biodiversity.

              Considering all the good that weeds do for us, why do we pull them up at all? Well, for one, many of us just don’t like the way they look. There are also certain troublesome plants like bindweed and poison ivy–which are hard to control or make us break out in hives–that are best eliminated. Yet, as the British gardener John Walker puts it, “weeds act kind of like living plaster” on open wounds. If we want to keep our gardens in a state of health, we need to replace them with plants and soil amendments that occupy a similar niche and help heal the ground that has been disturbed.

              Very often this is a matter of bringing in compost and mulch to restore the soil and make it more suitable for ornamental and crop plants. Since some weeds thrive in disturbed and degraded soils, it follows that they might compete less well in healthy ones. We might also plant things that thrive under similar conditions as the spontaneous vegetation that’s present in order to fill the same ecological space. For example, where you see a preponderance of nutsedge, plant a moisture-loving dogwood or Joe-Pye weed. Of course, this is a process, so don’t expect to get rid of your weed problems overnight. In the meantime, take a look at the plants that have arrived unbidden and consider the work that they’re doing.

You can reach freelance writer Brian Allnutt at brian.allnutt@gmail.com