Know Your Weed—Know Your Soil

A weed is just a plant in a spot where it is not intended to be. Flowers can be weeds too! We had sunflowers pop up EVERYWHERE the year after our sunflower maze. There is currently spearmint happily travelling from one hole to the next in my perennial tarp. Yikes! Mojitos, anyone?

Also remember some weeds can make you money! I had to swallow my pride and “harvest” Solidago, aka goldenrod, after Dave Dowling visited my farm and commented on how much amazing solidago I had! Face palm. I was so embarrassed of the chest-high weeds. But the next week I put them in the market bouquets and had so many positive comments!

We all think of a pristine, weed-free farm as the gold standard. But sometimes weeds are helpful. Weeds can be a great indicator of your soil’s health. An observant farmer can notice the subtle changes in weed populations in response to their soil management skills. They can reveal the soil pH, aeration, moisture-holding capacity, and even the nutrient deficiency or toxicity of the soil.

A few common indicator weeds I look for on the farm are dandelion (Taraxacum), Canada/creeping thistle (Cirsium arvense), lamb’s quarters (Chenopodium album), pigweed (Amaranthus retroflexus) and smart weed (Polygonum pensylvanicum).

Dandelions are very common. They spread across meadows, and the recognizable yellow tuft flowers dapple the countryside. Dandelions have a strong, deep taproot. They show up especially in compacted areas. The taproot is working to break up the hard soil and loosen the ground. I always find it hilarious seeing people rolling their lawns (compacting the soil) then having to spray or dig out dandelions! So, if you see dandelions you know your soil is compacted and you need to work at loosening it. If you are trying to remove dandelions, make sure to get as much of the root out as you can.

Canada or creeping thistle—I stake no claim to the name! But it is definitely here in this part of Canada. These thistles have a taproot so they are telling you that your soil is compacted and has heavy clay. Again, its roots want to work to break up the soil. These guys are resilient; if the root fragments break off when you are pulling them, each of those pieces will grow a new plant. Get them all out. Fun fact: goats LOVE thistles! When we would open a bale of nice alfalfa hay for the goats, they would find the dry spiny thistle and snatch it up instantly.

When lamb’s quarters pops up in your fields you can rest easy that there is high fertility or humus in the soil. These weeds show up in tilled soil and are fairly easy to get rid of. When the seedlings are very small (under 1”) you can go through with a “Garden Weasel”/tine hoe to uproot them and kill them before they are too attached. This method works great on a hot, sunny day. I call it weed-killing weather. Once the little weeds are disconnected from the soil they will fry in the hot sun! Such a satisfying sight.

Pigweed is another indicator of high fertility and humus in tilled fields. You can deal with pigweed much the same as lamb’s quarters. Get them when they are small and they won’t cause a problem. Pigs also do LOVE eating pigweed. Small pigweed and lamb’s quarters can also be killed when they are super small with a flame weeder.

Smart weed is one weed that I actually search out at times for wedding work. The hanging pink clusters are an amazing texture in design! With something to support them, I will also use them in bouquet work. But really, they are a weed. Smart weed is indicating wet conditions. Try to get smart weed out when it is small because when it gets larger the stems bend, and wherever the stem touches the ground it attaches and grows roots out of the part touching the ground.

To find more information about weeds in your area, search “weeds as indicators”. There are many research papers, books, and charts with lots of valuable information.

Next time you are out pulling those darn weeds, take a minute to look closer, and listen to what they are telling you.

Erin McMullen

Harris Flower Farm

Contact her at [email protected]