Identifying weeds might not rank up there with ridding the garden of the invaders, but it often drives me mad when I can’t identify a weed. It’s more important to know a weed from a desired plant or wildflower, so you know whether to leave it alone or destroy it before it spawns and takes over your garden.
So, how can you tell a weed from a flower? Here’s a definition I received from a weed scientist with New Mexico State University in their master gardener training materials: “A weed is any plant that interferes with the management objectives for a particular site or situation.” That’s actually a brilliant definition (must be because he is an expert). Here’s why:
One gardener’s weed is another gardener’s favorite fauna, but with some caveats. In other words, if you love dandelion flowers and want to leave them in your garden, then maybe dandelions are not a weed. If you leave purslane to grow because it’s an edible weed (as are parts of the dandelion), then more power to you. But if the purslane begins to cover your thyme or the dandelion chokes out the small area of grass you have in your lawn, do you shift them into the “Weed” column?
Another way to look at it is to peg a weed according to some criteria set by the Weed Science Society of America. According to their site, weeds have common characteristics, including:
- Production of way more seeds than normal – up to tens of thousands from a single plant.
- Long survival time for seeds, which can remain dormant in soil until just the right weather or other condition triggers growth.
- Rapid establishment (yes, they really can crop up nearly overnight).
- Mechanisms that support easy spread.
- Ability to grow in places where other plants can’t, such as between rocks or in poor, dry soil.
If you look at the one attribute that all of the points above have in common, it’s this: survival. I can’t count how many times we’ve sowed some flower or vegetable seed at just the right depth, watered it regularly and checked daily. Nothing. But weeds – they keep returning for encores, even when you try to destroy them!
Aside from persistence, the ability to outcompete nearly any plant and your best efforts to remove it, there are a few other ways to tell a weed from a regular plant when you’re examining it in your garden. For example, the characteristics that help weeds spread their seeds might show in their appearance. Hooks, spines and stickers make them harder to pull. And some have adapted attractive flowers to fool gardeners. A tap root often is a sign of a weed, or at least a plant’s survivability. You can pull and pull, but if you break the root off, it comes back and is somehow stronger than ever. Rhizomes or stolons also help weeds spread just underground, especially grassy weeds. And some weeds have asexual properties so that they can reproduce plenty of new plants with no floral fertilization.
In short, if a plant is wrapping around another plant, cropping up on, under or around a plant so that it affects your desired plant’s ability to use sun and water, call it a weed. We have some gorgeous volunteer wildflowers that come up each year in our garden, but we don’t keep all of them. If they crowd out another plant or cause so much shade around roots that a rose gets fungal during the monsoon season, they’ve got to go. I’ll keep a few of them, which means I’ll have to thin again in the future. But I won’t call them a weed.
I’ll post some of the worst New Mexico offenders in the future. For now, if you need help identifying weeds, check out the tool and external links under the WSSA’s Weeds section on their menu. I’ve also posted some new links on my Resources page.