When people find out that I have a MS degree in weed science they usually end up asking me if I can come take care of the weeds in their yard. I usually tell them probably not, but that I can tell them which weeds they have – which is half the battle. Weed identification has been a major part of my job – first as the weed biology and management lab instructor, and then as a presenter at the annual Utah Weed Control Association and Utah Weed Supervisors Association annual meetings.

When I took, and then taught for 5 years, the weeds lab at USU one of the major assignments was to create a weed collection. The main requirements for the collection were: there needed to be 50 specimens representing at least 10 plant families, and they needed to be well-pressed so that they were identifiable (not just a moldy pile of mush; or a stick). If I were taking that class this fall I could gather almost all the weeds I needed for the collection from my yard alone! After a quick listing of all of the weeds I have seen, pulled, or are currently growing in my yard, here is what I’ve come up with: 33 34 species representing 12 13 plant families.

 

In one small section of my one-day perennial border, there are a dozen (at least) different types of weeds.

Now, it’s not that I’m necessarily proud of the array of weeds in my yard. But I am impressed with it. As I’ve been spending a lot of time among them recently (it’s finally been cool enough to face them again) there is one aspect of the weed biology and management class that keeps coming back to me – knowing the weed life cycles.

When I taught the lab, the first month was focused solely on weed identification. In the classroom I would introduce 25 species a week – show some pictures, talk about key identifying characteristics, etc. – and then we would go out on field trips to some pre-selected sites where I knew we would see a variety, if not all, of the weeds I had just talked about. The next week, the students would be quizzed on 10 of the 25 species learned the prior week. Quiz questions included knowing the common name, the scientific name, and/or the life cycle of the plant in question. Every year students would ask why they needed to know the life cycle of the weeds. Every year I would tell them the same thing – knowing the life cycle of the weed will help guide management decisions and options.

 

Even though this was my answer for the five years I taught the lab, it didn’t really sink in to me the importance of this statement until this, my first summer as a homeowner. Knowing the life cycle of the weed really will help guide management decisions and options.

 

For example, annuals tend to put a lot of energy toward seed production. Which means they make A LOT of seeds. So if you have a pesky annual weed in your garden, a good management solution would be to prevent it from making seeds. Whether this means you pull it, mow it, burn it, or spray it is up to you. But you don’t want it making any more seeds. Sure, there are seeds still in the ground that will keep germinating as long as environmental conditions are suitable (i.e. it keeps getting watered and there is sufficient light), but you won’t be adding more seeds to the seed bank.

Though an annual, red root pigweed (Amaranthus retroflexus) boasts a hefty taproot. This helps it regrow during the season if it gets mowed or hacked off.; but it won’t regrow from that same root in the following season – it will do that from one of the thousands of seeds it produces.

At this point in the season the annuals have mostly matured and many have already dropped their seeds, so it will be tricky getting rid of the weeds without adding more seeds to the seed bank. However, most annual weeds need to be near the soil surface. Tilling and cultivation, while they may remove annual weeds or bury some of the seeds, will also bring other seeds up to the surface. To reduce annual weed germination, reduce soil disturbance as much as possible, apply a heavy layer of mulch (blocks light), and remove the weeds as they’re germinating with a light-handed hoeing or hand-pulling.

close up photo of salsify seed head

Western salsify (Tragopogon dubius) is a biennial – in the first year it remains a leafy rosette, in its second year it produces a showy flower with an even showier seed head.

If you’ve got a perennial weed, things get a little more complicated. Whether it is a simple or creeping perennial (more on that here) can dictate specific management strategies, but for either type just know that you’ll be dealing with both roots and seeds. This is (one of the many reasons) why field bindweed (Convolvulus arvensis) is so hard to get rid of – besides being a prolific seed producer, the creeping roots can send up leaves/rosettes at underground nodes. When you pull up one bindweed plant, you’re really just pulling out one part of a much bigger problem. Repeatedly hand-pulling a perennial weed will eventually weaken the root system to the point that it can’t recover, but that is a very long process indeed that needs dedication and patience. Many times, applying an herbicide in the fall, while the plants are still actively growing but pulling resources from their leaves to their roots, will provide effective control. (As always, read and follow all herbicide labels).

pic of field bindweed creeping root

New plants can grow from root nodes; on this particular section of field bindweed root we can see four individual rosettes forming.

And then there are those weeds that can’t make up their mind. They could be an annual. Or maybe a biennial. Or perhaps a short-lived perennial. Common mallow (Malva neglecta) is one that falls in this category – depending on environmental conditions it can complete its life cycle in as little as one year or it can live for a few (to many) years. As always, you’ll want to prevent seed production as much as possible, but you’ll also want to remove it from the ground when it’s small so it can’t build up it’s taproot to live on for another year.

close up photo of mallow flowers and leaves

Common mallow (Malva neglecta) is one of those tricky ones – it can be an annual, biennial, or perennial depending on how it’s feeling. Or rather on the environmental conditions it finds itself in.

As you’re making a to-do list for fall garden clean-up, don’t forget the weeds. Taking care of them now will help reduce (not eliminate, sorry, there’s no silver bullet for that) what you have to contend with next year.

What other fall garden chores are on your to-do list?