Do you fight weeds in your lawn, flowerbeds or garden? If so, those weeds actually are trying to tell you something about the condition of your soil. Farmers and gardeners constantly fight weeds, but those weeds can have a useful purpose. They act as soil indicators. The most prevalent weeds growing in an area can indicate whether the soil is acidic or alkaline, whether that soil is a healthy, balanced soil, or is nutrient deficient. Weeds can indicate a poorly draining soil, or a soil that is unable to retain moisture. So, in reality, weeds have a lot to tell us if we know "how to listen" by knowing how to interpret their presence.

Look for some of the most common and widespread weeds to use them as a soil pH indicator. An acidic soil has a pH below 7. The presence of both dandelion and common mullein can indicate an acidic soil, but mullein also can indicate a soil with low fertility. If mullein is seen alone, it could mean several things, but seen along with dandelions, it could indicate an acidic soil. Hydrangeas and cornflowers are excellent indicators for soil pH. Their flowers are pink in acidic soil and blue in alkaline soil. Other common weeds that are indicators of an acidic soil are curly dock, dandelion, knapweeds, mosses, nettles, wild viola, plantain, and wild strawberries. More desirable plants that grow well in acidic soil are azaleas, blueberries, endive, hydrangeas, rhododendrons, rhubarb, potatoes, shallots, sweet potatoes, and watermelons.

Alkaline soil has a pH higher than 7. Some weeds that can indicate alkaline soil are Roman (true) chamomile, black henbane, stink weed, nodding thistle, and wild carrot. Asparagus, broccoli, beets, lettuce, muskmelons, onions, and spinach are desirable plants that do well in alkaline soil.

Weeds that indicate a hardpan soil are field mustard, horse nettle, morning glory, pennycress, and quack grass. Bok choi, broccoli, cabbage, cauliflower, and mustards grow well in this type of soil. Previously cultivated soil will have predominately: carpet weed, chickweed, dandelion, lamb’s quarter, plantain, purslane, ragweed, and pigweed.

Weeds that indicate a wet, poor draining soil are bindweed, bull sedge, Canada goldenrod, cattail, coltsfoot, dock, foxtail, poison hemlock, horsetail, jewelweed, Joe-Pye weed, May apple, mosses, and stinging nettles. Wet spots, while obvious during the rainy season, could appear dry at other times. A predominance of these weeds is an excellent indicator that the area will be soggy at some time during the year.

A healthy, fertile soil will have a pH of 6.2 to 7. Weeds indicating a fertile soil are burdock chickweed, chicory, dandelion, lamb's-quarters, pokeweed, purslane, Queen Anne's lace and velvetleaf. Vegetables such as broccoli, corn, lettuce, melons, peppers, squash, and tomatoes are all heavy feeders and will thrive in a fertile soil. A poor or depleted soil will have weeds such as broom sedge, wild radish, sheep sorrel, wild parsnip, biennial wormwood (Artemisia) and yellow toadflax. Beans, beets, carrots, legumes, parsnips, peas, radishes, sage, and thyme will tolerate poor soil conditions and actually perform well in depleted soil.

While certain weeds are indeed fairly reliable indicators of growing conditions, a soil test is the surest way to confirm a soil’s deficiencies. Test results will indicate what amendments are needed for specific plants and crops. Soil test kits are inexpensive and available at the Penn State Cooperative Extension office at 670 Old Harrisburg Road. There will always be a battle between gardeners, farmers and weeds. But, weeds can have value as soil indicators, so learn what their presence may be telling you about your soil.