Weeds And Seeds

Mike offers advice on reclaiming areas that have been taken over by weeds, in particular weeds that have set seed. Florida Nursery Grower Landscape Association Certified Horticulture Professional classes Covers subjects about horticulture and pest management for the grower and associated industries

Controlling Weeds That Have Gone to Seed

Q. I’m looking for advice on how to get an area of my garden back under control without using chemicals . I failed to keep up with the weeding in a section of my vegetable garden that is about fifteen by 30 feet. It had crabgrass, clover and a few other weeds that went to seed. I ripped them all out as best I could, but can’t get all the roots out—and I can see that a lot of seed has scattered on the surface of the soil. I wonder if covering the area with impermeable black plastic until next May would kill everything? Or maybe it makes things worse by keeping the area warm enough for the weeds to survive the winter?

—Kat in Leesburg Virginia

A. Let’s start with the black plastic idea.

Wishful thinking. Weeds need no help surviving winter; and only clear plastic stretched tight over a perfectly prepared area for an entire summer can kill weed seeds. It’s called ‘soil solarization’, and this description of the proper technique is not my opinion; it’s the only way that diligent researchers got it to work. (Here’s the details in a very popular previous Q of the Week .)

Her best bet now is to use a ‘flame weeder’—a hand-held, propane-powered garden torch that shoots a small flame out the business end of a long shepherd’s hook-like wand—to slowly toast one small section of the infested area at a time, preferably on a hot day when that soil is bone dry. It’s much less work, you get to stay upright while you deactivate those weed seeds, and every little ‘pop’ you hear is an emotionally satisfying sign that you’re doing it right.

(I’ve always been emotionally satisfied by my flame weeders. [Mom said it was OK to be easy; just not cheap.])

So–what about those roots still in the ground?

It sounds like Kat had a typical round of frantic but useless pulling. I suggest she let those roots re-sprout, and when they’re tall enough, soak the soil thoroughly and pull gently at their base. (Be sure to compost those pulled roots with lots of soil still attached; they’re full of nutrients, and they’re the perfect ‘green material’ to mix with shredded fall leaves. And the attached soil contains lots of microbial life to get that compost cooking!)

In general, this is the best way to handle weeds of almost any size: wait until right after a heavy rain or soak the soil for hours—really saturate it—and then pull ‘low and slow’; get down to where the plant meets the soil and pull slooowly and gently. That’s how you get the roots out the first time.

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‘Angry yanking’ may seem emotionally satisfying, but it doesn’t get the job done. And it tends to be the panicked tactic of choice for large areas that seem insurmountable. Better to slow down and spread the job out over a week or so. An hour a day of doing it right in small area after small area gets rid of the weeds without you needing a corner man.

Now: why did I say ‘weeds of almost any size’?

Because, as Kat discovered, yanking weeds that have already gone to seed spreads the seeds. When weeds are seedy, don’t pull right away. Instead use that flame weeder to incinerate the tops of the plants. Then run the flame up and down the sides of the plants; wherever you see seed pods. The torch will toast those seeds, and you can then pull out the plants without planting next year’s crop of weeds. Bonus: Many weed seeds look like Munchkin fireworks when they pop!

(Yes, the words ‘easily amused’ do come to mind; saves me a fortune on my cable bill.)

Anyway; next season, delay planting these areas until any missed weed seeds have germinated and been growing for two weeks. Then carefully and methodically slice them off at the soil line with a hoe that has a flat super-sharp blade, like a diamond hoe—creating what’s known as a ‘stale seed bed’. And whatever you do, don’t till the soil; tilling plants weed seeds!

An alternative tactic would be to use the natural pre-emergent herbicide, corn gluten meal . Just as you would do with cool-season lawns, applying corn gluten meal at the rate of twenty pounds per thousand square feet in the Spring (when forsythia and redbud just begin to bloom or when the soil temp reaches 55 degrees F. measured four inches down) would prevent a lot of dormant weed seeds from sprouting. Heck—because those seeds are on the surface, ‘CGM’ might provide astounding control. (Be sure to apply as per package directions.)

Now—that would also put a lot of Nitrogen into the soil, so I would then use that area to grow a non-fruiting, but Nitrogen-hungry crop like sweet corn , field corn, popcorn, salad greens, potatoes, onions or other things I’m not thinking of right now.

Corn of any kind would be especially ideal; ‘maize’ loves a Nitrogen-rich soil, and 15 by 30 would be a perfect size to seed a big patch and get lots of nice full ears. (I personally vote for popcorn—super-fun to grow!~) You just have to wait six weeks after applying the CGM or pre-sprout the corn seeds, which I recommend anyway. (You’ll find those pre-sprouting details under C for corn [maybe] and under P for peas [definitely].)

In addition, the way she describes this area, we have to assume that it’s a flat earth garden; a design—or lack of design—that guarantees maximum weed woes. You get a lot more eatin’ with a lot less weedin’ from raised beds . Four by eight is the ideal size for each bed, with two-foot-wide walking lanes in between. Because you build the growing area up to a foot above the soil line, grassy weeds like the clover and crabgrass she specifically names can’t migrate in from the outside. And you can just mow the actual lanes to keep their weeds under control—no pulling.

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And the cool air of fall is perfect for getting outside and doing some raised bed building! And if you build those beds now, they’ll be ready to plants in the Spring. Hint; hint….

Final note: But if Kat does take the ‘corn gluten meal followed by some kind of corn’ advice, she should build those raised beds in other areas of her garden. Corn is one of the few crops that does better in flat earth than raised beds. Sounds like a plan!

Weeds And Seeds

​H orticulture in Southwest Florida is unlike anywhere in the world. Growing conditions are often ideal. Warm year-round temperatures, generous rainfall, and sunny days encourage plants and people. This microclimate offers a unique palette of foliage, flowers, and fruit.

Enthusiasm about plants is the beginning of being a great horticulturist. Knowledge, effort and experience complete the package. You are most productive and successful when you are familiar with seasons, soils, plant selection, attractive, useful arrangement, insects, diseases, weeds, and many unseen enemies of plant life.

Our objective is to give you a wide exposure to Florida ornamental horticulture, focusing on the southern zone, concentrating on Lee and Collier counties. Our classes are designed to give you useful, local information and to help you to pass the Florida Nursery, Growers and Landscape Association’s (FNGLA) Certified Horticulture Professional tests.

Classes

The first class starts this Thursday, August 4th. There are still a few openings but no time to mail in your forms. So just print out the registration form from the next page and bring it along with your payment.

You will enter Naples Botanical Garden on Bayshore Drive and turn on your first right to parking. We will meet in room KC 126.
Signs will be posted.

Feel free to bring your own drinks and snacks as there are no vending machines. This is a non-smoking location.

I will be there at 5:30 to process any registrations and will start the class at 6:00.
See you there!
​Bob Cook FCHP

Plant Identification

In our certification program we are responsible for identifying 259 palms, trees, shrubs, foliage plants, vines, ground covers and bedding plants. This link shows you clear photos , arranged by those categories.

Bob Blog

In this blog I have some horticultural fun. At the bottom of the front page you can choose from categories like; Bedding plant trials, trade shows, salsa recipe, tomatoes, peppers, bad landscaping, garden benches, fairy gardens, poinsettias, and much more.

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Weeds And Seeds

The last post demonstrated the remarkable ability and unique features of aphids that allow them to rapidly boost their numbers and colonize their hosts in favorable conditions. What about weeds? What features give them the ability to rapidly colonize a potted crop or planted field? Many plants become weeds because they have the powerful trick of producing many many seeds. Seeds are dispersed by wind, insects, animals, or by their association with our nursery tools and machinery. Often, these seeds are long-lived in the soil. Consider these statistics:

Probably some unfortunate graduate students or field assistants in 1954 were given the task to count weed seed of hundreds of common weed species from about 50 plant families in North Dakota. The table above is just a sampling (Stevens 1957). In most cases a single plant, judged to be of average size and growing where competition was low, was harvested at maturity or when a maximum number of seeds could be obtained. The plants were air dried for two weeks or more, threshed and cleaned to re-move immature seeds, empty florets, etc. All of the sampling methods are described in the Stevens reference given below.

So basically left on their own, weeds have a profound ability to produce seed. Some seed are not viable, some germinate immediately, and some persist, perhaps for years, in the soil as a “seed bank”. This bank represents the holdings of weed seeds in the soil. Place a “deposit” of seed in this bank, and your “interest” is compounded in a big way. An interesting experiment with velvetleaf (Abutilon theophrasti) an important weed in soybean crops demonstrated this (Hartzler, 1996).

Velvetleaf is a prolific seed producer and seeds are long-lived. In 1990, replicated experimental plots were planted with soybean and then with one of three velvetleaf densities: 0, 0.2, and 0.4 plants per square meter. In subsequent years, the experiments were maintained in a corn-soybean rotation. Weed densities were determined at crop harvest for four years. As seen above– even with competition from the crop plants– velvetleaf density increased dramatically for years following the very sparse initial planting of the weed. There were even some velvetleaf plants seen in the untreated “0” plots, even though the plots were hand weeded to reduce seed production for 5 years prior to initiating the study.

The number of weed seeds in in the soil can range from near 0 to over 1,000,000 per square yard, and most weed seeds are between 0 and 5 years old. A small number of seed can remain viable for decades or more. With this knowledge, one of the most important principles of weed management is to “never let weeds go to seed”. Never.

References:

Stevens O.A., 1957. Weeds, Vol. 5, No. 1 (Jan.), pp. 46-55

Hartzler R.G. 1996. Velvetleaf (Abutilon theophrasti) Population Dynamics following a Single Year’s Seed Rain