Weeds

Early Spring Lawn Tips for Fertilizer and Pre-emergent Timing

Maryland Grows3 Comments
Speedwell is a winter annual weed. It will end its life cycle and die naturally once we have consistently warm temperatures. Photo: G. Rinehart

The warmer-than-normal weather during February had many people thinking about an early start to lawn and garden season. However, as temperatures have dropped and been below normal for much of March, it looks like we may have a couple more weeks before lawns really start growing. Lawn growth and crabgrass emergence are related to soil temperature, which is slower to change than the air temperature. While I have heard reports of soil temperatures topping out in the mid-50s for a day or two, it’s important to remember that in order to germinate crabgrass needs soil temperatures around 53-55⁰ F sustained for 5 days. These two things lead to a few questions, particularly pertinent this year when February felt like March and now March feels like late February.

Should I fertilize my lawn now?

While the legal window for applying fertilizer to lawns in Maryland began on March 1, that doesn’t necessarily mean you should fertilize your lawn just yet. Unless the grass is actively growing (which is dependent on warmer soil temperatures) it likely won’t take up and use the fertilizer—so you are better off waiting until the lawn is actively growing. Temperatures consistently around 60 and enough growth to warrant a second mowing are pretty good indicators of this. Keep in mind that if you fertilized your lawn in the fall you can probably wait until after the “flush of growth” in the spring (usually April/early May) and then schedule your spring fertilizer application for after that “flush” and leading into summer—usually around mid-late May. If you didn’t fertilize last fall it is tempting to try to “jump-start” the lawn in early spring with a fertilizer application, but hold off until the soil temperatures are consistently warmer and highs are around 58-60⁰ F on a regular basis.

Should I apply crabgrass pre-emergent now?

I would wait until soil temperatures are 53-55⁰ F sustained for 5 days. Keep in mind that your best defense against crabgrass is a dense turf that crowds out crabgrass seedlings. So, if you have good turf density and mow at 3” or higher, your overall crabgrass pressure should be lower anyway. The typical recommendation is to wait until the forsythia is “half green-half gold” (or even a little earlier), but with the warm February we had, that indicator may or may not be as accurate this year. You can check soil temperatures for your location at the following website: https://www.greencastonline.com/tools/soil-temperature. 

Is there harm in applying crabgrass pre-emergent too early?

Probably not, unless it’s applied several weeks early and the product starts to break down before crabgrass even starts germinating. If you want to maximize the period of time your crabgrass application is effective, wait until when conditions are conducive to crabgrass germination and then apply it.

grassy lawn weed called roughstalk bluegrass
Roughstalk bluegrass (Poa trivialis) is a cool-season weed that shows up in early spring. If you only have a few patches, you can dig them out by hand (including the roots) and overseed to fill in the bare spots. Photo: G. Rinehart

On another note, this is now the time of year when many winter weeds become more noticeable as they are likely producing flowers and setting seeds. While you can apply selective products to control these weeds, remember that these winter annuals like chickweed, purple deadnettle, speedwell, henbit, etc. are almost at the end of their lives and will die naturally once we have consistently warm temperatures. Another weed often noticed this time of year is the grassy weed called roughstalk bluegrass (Poa trivialis). Seeds of this grass are often a contaminant in turfgrass seed mixes (the cheaper the seed, the more likely you will have weed seeds) and this grass starts growing much earlier than tall fescue. As the temperatures warm, it is not as aggressive and noticeable. There are few selective control products that are labeled for roughstalk bluegrass and they tend to be restricted to professional sites and/or are expensive. If you only have a few patches in your lawn, digging these out (including the roots) and then re-seeding the spot with a soil-tall fescue mix is the best control approach for most homeowners.

By Geoffrey Rinehart, Lecturer, Turfgrass Management, Institute of Applied Agriculture, University of Maryland. Read more articles by Geoff.

Weeds are a challenge, even in a raised bed garden

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In the bottom two middle squares of my raised bed garden, the spinach and leaf lettuce is growing from last month, but now it appears like there are some unwanted plants as well — weeds! In just a few short weeks, our garden has been overtaken by weeds. The weed seeds came from the topsoil I purchased. Weeds are a problem when you have a garden of any size, unless you use new, sterile, soilless growing media each season. Knowing what you planted will really be important so you can be on the lookout for the seedlings, and remove just the weeds.

Seedling leaves (cotyledons) often look completely different from the first true leaves that come out later. One characteristic that can help you in figuring out if you have a weed or a plant you want to grow is by looking at the number of leaves that sprout from the seed. If the plant has one seedling leaf, it is called a monocot (monocotyledon). This includes plants like onions, corn, and grasses. If the plant has two seedling leaves at germination, it is called a dicot (dicotyledons) and includes plants like tomatoes, beans, potatoes, spinach, and lettuce. Dicots are sometimes referred to as broadleaf plants. Many times selective herbicides work on either monocots or dicots but not both types of plants; that’s what determines which plant will be killed by the herbicide or which will be resistant. Non-selective herbicides will kill both monocot and dicot plants.

Sometimes people get really upset when I call a plant a “weed.” Please remember that many plants can be designated as weeds. The simple definition is “a plant growing where it is not wanted.” So even though weeds can have desirable characteristics, when it is a plant growing where it is not wanted, it is a weed. Weeds compete for sunshine, water, space, and nutrients in the garden, and some can be hosts for diseases and pests.

As with most gardening tasks, addressing the problem early and often is the best advice. Being able to identify weeds when they are small is one of the skills that I continue to hone each growing season and it takes practice and time. Knowing what you planted and where you planted it is the first step in knowing what may or may not be growing. Virginia Tech has a nice identification guide that lets you answer questions about the specimen and points you to a possible answer.

Left: Grass seedling, an example of a monocot. Right: Ragweed seedling, an example of dicot.

Examples of dicot weeds. Left: Lambsquarter (larger and smaller stages). Right: Smartweed (see the thumbprint in the center of the leaves). 

I will be using mechanical control methods (hand pulling or a small hand shovel to remove the weeds) because it’s such a small area.   

In our commercial high tunnel operation, we use a physical barrier as our first line of defense in weed control. Wind can cause hardships with keeping landscape fabric held in place, but we use 6-8’’ long landscape pins to hold it down.

Here is information on managing weeds organically.

The left photo shows damage as it appeared the morning after the frost. Right: shows what the damage looks like a week later. It hasn’t killed the plants, but they will be set back from the frost. 

We have had some very chilly night temperatures which is not too uncommon here in the mountains. Our expected frost-free date is June 5th, so I’m looking forward to putting in some warm season vegetables in the coming weeks — tomatoes, peppers, green beans, and maybe a summer squash are on our list.

Weeded garden bed

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland, edited by Christa Carignan, Coordinator, Home & Garden Information Center, University of Maryland Extension. See more posts by Ashley and Christa.

No-till gardening and weed barriers

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In a mid-March post, I wrote about the advantages of using heavy-duty weed barrier fabric to smother weeds and create a no-till plant bed. In mid-June, I found myself with two beds that were starting to get weedy. The winter cover crop that had protected the soil was quickly decomposing and crabgrass and broadleaf weeds were emerging.

Weeds
Rapidly growing weeds are quickly brought under control with weed barrier fabric.

I threw on 3-ft. wide strips of the weed barrier material and after five days of very hot weather all of the vegetation was dead. Continue reading →

Q&A: Is this giant hogweed or poison hemlock?

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poison hemlock
Poison hemlock can be mistaken for giant hogweed

Q: I think I might have giant hogweed on my property, or maybe it is poison hemlock. How can I tell for sure?

A: Giant hogweed (Heracleum mantegazzianum) was found recently in Clarke County, Virginia, and it has raised awareness and concern about the plant – and rightfully so. The plant produces toxic sap that can cause very severe skin inflammation. We have received a lot of questions about it lately.

poison hemlock
Poison hemlock Photo: E. Nibali

What you have here is NOT giant hogweed. It is poison hemlock (Conium maculatum), which is much more common. The ferny foliage makes it possible to distinguish it from giant hogweed.

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What Can I Do About All These Weeds?

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Ground Ivy
Ground ivy or creeping Charlie (Glechoma hederacea). Photo by Betty Marose

The famous quotation about the certainties of life which we all know includes death and taxes should also mention weeds! They are sprouting up all over. Even the most meticulously tended landscapes are not immune.

Where to Begin?

The first step is identification. You need to know your opponent. Control is more attainable if you know whether it is a grassy or broadleaf weed. Is it an annual, perennial or biennial? When does it germinate? Fall, spring, or summer?

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What Can I Do About My Neighbor’s Plants Coming Onto My Property?

Maryland Grows7 Comments

bamboo
Bamboo. Photo: Chuck Bargeron, University of Georgia, Bugwood.org

Maryland property owners are limited to self-help when dealing with plants encroaching on their properties. This is not legal advice.

Have a neighbor who has planted bamboo or another invasive plant species near your shared property line and now that plant has started encroaching on your property? What can you do in this situation? Maryland has only one decision discussing damage from plants growing on a neighbor’s property. In Melnick v. C.S.X. Corp., the Court of Appeals of Maryland limited landowners to self-help to remove invasive plant species from growing on your property. The courts in Maryland have found that “it is undesirable to categorize living trees, plants, roots, or vines as a “nuisance” to be abated. Consequently, we decline to impose liability upon an adjoining landowner for the “natural processes and cycles” of trees, plants, roots, and vines.” (Melnick, 520-521). Self-help means it will be up to you to remove the roots, limbs, vines, and other plant debris and not the neighbor who planted the invasive plant species. A neighbor cannot seek damages in court for the damages caused by the invasive plant species.

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Black Covers Can Put Weeds to Bed… For Good

Maryland Grows5 Comments

Have you experienced one or more of these garden scenarios?

  • It’s early April and chickweed, henbit and other winter annual weeds are growing so thickly in a vegetable or flower bed that the soil can’t be seen.
  • The winter rye cover crop you mowed last week is growing back.
  • You tilled and raked a bed that you couldn’t plant right away and now weeds are coming up everywhere.
  • The rainy summer weather is favoring weeds over crops so that the weeds are taking over walkways and dominating beds that you want to plant with fall crops.
  • Neighboring plots in your community garden have been abandoned and weeds are growing wild and reproducing!

I can’t bear to look… I’m going back inside

This stirrup hoe is great at removing large weeds, but brings lots of weed seeds up to the top two inches of soil where they have a good chance of germinating.

Un-controlled weeds compete with garden plants for water and nutrients, are hosts for insect pests and diseases, and can demoralize the toughest gardeners. Tilling, pulling, chopping, and hoeing are all fine weed control techniques under the right conditions, but they also disturb soil allowing even more weed seeds to germinate and flourish.

There’s another way: occultation. The common dictionary definition is “an event that occurs when one object is hidden by another object that passes between it and the observer.” For gardeners and farmers, it’s covering the soil to create a dark, warm, moist environment. In 2-4 weeks, this no-till technique can:

  1. smother and kill young weeds
  2. smother larger weeds and grasses
  3. accelerate the decomposition of mowed cover crops and weeds
  4. promote the germination of weed seeds and then smother the seedlings

Weed barrier pinned down over a bed filled with winter annual weeds. It was ready to plant in two weeks. Tough perennial broad-leaf weeds and grasses may be weakened but not killed.

Continue reading →