The MN wildflower blog

Jeff from Stillwater writes:

I started out with tilling my lawn into a garden 10 years ago. The first couple of years I was getting your typical weeds like any gardener. Then in one year I had 30 cubic yards of dirt brought in and I got my hands on free manure,not sure from what animal. I know they do have donkeys and goats. So I am not sure of the two it came from.My garden was a field of green by the middle of summer and I couldn’t keep up to this weed. It took everything over. Its the shaggy soldier(Galinsoga quadriradiata). I used round twice last fall and sprayed my whole garden. This year when they got 8-10 inches tall, one could not see any dirt it was so bad, I sparyed round up again,they all died. A few more came up about 4 inches and alot more are about 1/2 inch tall so I sprayd them again on 7-18-11. This is the only year I didn’t till my garden. What can i do to get rid of this weed. Thank You, Jeff M. – Stillwater, Minnesota

Dear Jeff:

Galinsoga quadradiata is an annual weedy species introduced from the near tropics that does quite well in our severe winters. Each plant can produce thousands of viable seeds in a single season. The art and skill of gardening is nothing if not “weed control”. Both perennial and annual weeds present their own challenges and of the two, annuals can be the most frustrating.

shaggy soldier - Galinsoga quadriradiata

While people have expressed their dismay at my recommendations for use of herbicides, I’ll argue that like many other modern inventions, they are a useful tool in solving weed problems and their environmental impact minimal if used correctly. For dealing with many aggressive invasive species such as buckthorn, oriental bittersweet, etc., etc., etc. the medicine is not nearly as environmentally toxic as the disease.

In your case, the use of glyphosate (Round-up) is inappropriate for the problem. Round-up will quickly kill most annuals but has no impact on the seed bank and usually within days you have germination of a whole new crop. Repeated applications just dump chemicals into the environment to no good effect.

Round-up is a very effective translocative herbicide and should only be used against perennial weeds. Once you have knocked them out (and yes – it may take several timely applications) you should never have to make an application again.

Future Woodland Wildflower Site

On this site that is planned for a future woodland wildflower garden, we sprayed the entire area with both Round-up and Trimec – mid-summer 2010 – for persistent perennial grasses, woody shrubs and perennial bitter nightshade. Following treatment we did extensive grubbing of larger rootsystems of like woodbine that our herbicide selection wouldn’t handle. We followed this up with a heavy layer of free woodchips dropped off by a local tree company. Thee woodchips will persist for several years as a weed barrier which in time helps wear done the seed bank. We are also getting in small trees to create the future shade needed by the species we’ll fill it in with over time. We still need to do regular hand weeding of emerging seedlings here and there – especially silver maple – but the work isn’t over whelming. As you can note we’ve thrown in some vegetables to get some productivity out of the site for now. However woodchips are tremendous consumers of nitrogen for the first few years and we’ve spot placed 10-10-10 fertilizer around the vegetable hills to over come this initial shortfall. Once we get our hands around the seed bank and can start filling in with desirable native shrubs and forbs we should never have to apply herbicides or fertilizer to the site again. That doesn’t mean the planting will become completely self sustaining at some point. Weed pressure from invasive species like Canada thistle and even dandelions require diligent long-term management. It will never be any other way with land ownership.

For annual weeds in the home landscape – nothing replaces diligent mechanical control. Since you are battling the seed bank and not underground perennial roots systems, it is a long term commitment. The “average” seed bank life is 7 years.

While there are “pre-emergent” herbicides marketed to the home gardener, I have rarely seen them effective. These are designed to kill seeds as they germinate in the top several inches of the soil and are effective for only one season. In theory, once put down they create a barrier on the soil surface preventing seedling production for that season.  But if that “barrier” is disrupted or disturbed for any reason, new seedlings immediately erupt through the breach. This type of product is what is used in crabgrass preventer, with fairly good success if applied correctly, in the home lawn. One reason for this is that it is easier to avoid disturbances in a lawns surface soil than it is in a flower or vegetable garden.

In a vegetable or flower garden with bare soil between plants, not only does a lot depend on both timing and conditions of application, but the open bare soil is much more subject to disturbance. Heavy rains such as we’ve seen this year can easily leach out the herbicide or erode it away in patches where new weeds quickly proliferate. The new weeds will require mechanical removal which just adds to the disturbance and soon you are back to square one. You just dumped some chemicals into the environment and you still have weeds everywhere.

I’ll state here and now that “gardening” is a persistent daily activity where the task is to be more persistent than your adversaries – in this case the annual weeds. If you approach this task like a weekend warrior with several major assaults during the growing season and then only when you have lost all track and sight of what you planted in the first place – you will never get a head of the eight ball. If this still works for you even though you are frustrated to tears – keep up the good fight? Myself, I would never tolerate this prospect forever and would quite gardening all together.

1 year old vegetable garden

Having said all this, people might ask why I don’t apply the same persistence against persistent perennial weeds like Canada thistle, quack grass, yellow nut sedge, Kentucky bluegrass and even common native milkweed – I can assure you I’ve tried. You have to be some kind of self-flagellating saint to take on that mission. Perhaps you might win someday but odds are you won’t. I prefer a little medication and get it over with so I can get the area into useful production as soon as possible. This is why I stated earlier that annuals can be more frustrating than perennials. With perennials there are effective herbicides that used in the short term provide effective long-term or even permanent control of the target weed species. The annual weeds will be enough of a challenge for anyone who basically views life as requiring some kind of penitence.

In the image of the 1 year old vegetable garden – this site was treated with glyphosate in late 2010 to knock out perennial quack grass and the original turf grasses – kentucky blue and fine fescue then hand tilled in spring of 2011. The soil contains a huge seed bank of crabgrass, foxtail, corn speedwell, oxalis, purslane and prostrate spurge. The mulch used here is one-year old rotted straw saved from a strawbale gardening project last summer. Time spent weeding is minimal to non-existent.

From the sounds of your letter, you have applied glyphosate enough times that perennial weeds should be non-existent. Put the danged stuff away and apply some elbow-grease. The next step is a nice little garden hoe – my two favorites are the hula-hoe and a small triangle hoe. Even these are only taken out when I’ve been a little remiss at my daily routine. I spend at least one hour everyday in the garden and most weeds are pulled by hand. Another tool I use is my grass clippings from what we still have in turf. Just a ½” layer of clippings is far more durable and effective a barrier to annual weed seeds than any pre-emergent herbicide I’ve attempted. If weather or other disturbance creates some gaps during the growing season – next time you mow the lawn – throw a little more in there.

New strawberry bed

This new strawberry planting was treated with glyphosate in summer of 2010 to remove brome and reed canary grass. Here the mulch used is from bi-weekly clippings from the lawn. The site requires monitoring and an occasional weed pulled here and there. Grass clippings do not create the same nitrogen stress that woodchips do and in fact return most of their nitrogen load back to the soil within weeks of putting down.

We’ve begun our neighborhood introduction to alternative lawns by starting small with this isolated boulevard patch on the corner. This site was sprayed with glyphosate in late 2010 and then twice again this spring for a heavy infestation of quackgrass. I can not over state the requirement to eradicate aggressive perennial grasses from a site before you attempt putting in any natives. The grasses will come back from any viable underground rhizomes you’ve missed and they will degrade the planting over time. I think cities would be less resistant to this idea if better implemented. Too many start out as good intentions but eventually look like eye-sores when not prepared properly in the first place. This was seeded with side-oats grama in May of this year and is a pure stand what you see in the picture. I have rigorously hand weeded out all of the annual foxtail and crabgrass seedlings. While a pain in the ars initially it has helped speed up the establishment of a close canopy of native grass in less than three months time. While I had not expected to so soon, I’ve already planted a couple of native forbs (smooth & sky-blue asters, showy goldenrod and royal catchfly) that should bloom for me this season. While i should never have to water, fertilize, treat with herbicides or mow this “flower garden” again. If I don’t diligently tend to this and any “garden” over time, nature’s course will work to over run it with any opportunistic weedy species should I give it that opportunity. This is true of whatever you plant for whatever purpose.

Boulevard prairie garden

Gardening is an active life style that like anything else productive requires perseverance and commitment. In your case it will take at least 3-4 years before you see a significant reduction in weed pressure from the shaggy soldiers. It is a “learned practice” that, like anything – once you get the hang of it – it doesn’t seem so much a task as perhaps more a moment of meditation. If you need motivation at being consistent over time, keep in mind that if you work hard at it for a number of years and then one season go into relapse; you’ll basically have thrown all your hard work out the window. While it takes on average seven years to completely diminish a seed bank, it takes only one year for the weeds to replenish it.

Good luck and may the Ancient Spirit of Gardening be with you.

Petyer