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by Nanette Londeree, Master Rosarian

If you’re a gardener, you certainly don’t need an introduction to weeds. They can be a nuisance and detract from the overall appearance of the garden, but more importantly, they can rob the soil of precious water and nutrients. Especially in our Mediterranean climate and the ever-increasing cost of water, you don’t want to be giving it away. Weeds can also serve as hosts for insect pests and pathogens, provide cover for rodents and be allergens to many people (think hay fever or poison oak).

Weeds, simply put, are plants growing where they aren’t wanted - those pesky things around the base of your roses or trees, in amongst your perennial bed or creating a mosaic pattern in your lawn. Almost any plant – from grasses to trees to shrubs, under the right conditions, can be considered a weed. I have a very busy squirrel that plants acorns in my rose bed, so oak tree seedlings are one of my major weeds! They come in a myriad of shapes, colors, sizes, and degrees of tenacity…some are pretty easy to control, while others, like bindweed (or what I consider the Kudzu vine of the west) seem to withstand and almost thrive on significant abuse. Common weeds (both grasses and broadleaf plants) that plague our gardens are annuals like bluegrass, crabgrass, mallows, purslane and spotted surge; perennial types include bermudagrass, bindweed, dandelions, nutsedge and oxalis.

An overall weed management program involves preventive and removal methods, most relying on cultural practices and mechanical and physical means of removal. Preventing weeds from sprouting will make your life a whole lot simpler, especially given how prolific some types are in producing seeds. Take purslane as an example - it can generate over fifty thousand seeds from one plant!

  • Cultural methods – whether you are starting a garden from scratch or alternating what you already have, you can build in weed suppression through design, habitat modification or horticultural controls.

  • Design portions of your garden with no water or soil (driveways, paths, patios) to eliminate the elements necessary for a plant to grow.
  • Reduce the available water to planted areas (using drip irrigation) to make life difficult for weeds to germinate and sustain growth.
  • Crowd plants to reduce the available space—it can inhibit seed germination.
  • Inspect new plants for weeds before introducing them to the garden; don’t plant unwanted hitchhikers!
  • Ensure any homemade compost has gotten hot enough to kill weed seeds; otherwise you may have tomatoes and other volunteers invading the planting beds.
  • Mechanical and physical methods -are the most common, and generally easiest way to prevent or remove weeds:

  • Mulch, mulch, mulch! Add organic mulches (compost, softwood bark chips or nuggets) around plants; not only will it look neat and tidy, it will reduce the amount of water you use while cutting down on weeds.

  • Introduce a weed barrier by laying down permeable landscape fabric on new beds; open up only the required space for new plants, then top with mulch.

  • Eliminate weedy areas by sheet mulching. Cover with multiple layers of newspaper, then top with a layer of mulch to smother weeds.

  • Cook those weeds! If you have the time, and want to remove weeds from a large area, consider soil solarization – it’s an effective eradicant when preparing a new planting bed. Clear plastic sheeting placed over the area to be treated for a period of four to six weeks during the warm summer months can kill both existing weeds and their seeds.

  • Remove weeds by hand puling or using a hoe while they’re young and before they set seed. Make sure to remove the whole plant, roots and all. Some perennial weeds like stubborn bindweed, will re-grow if even the tiniest shred of roots remains.
  • Dandelion

  • Chemical methods—Generally, for most home landscapes, chemical treatment is a last resort as it requires an understanding of the lifecycle of the weeds to be eliminated, soil characteristics, weather and location as well as the multitude of product choices - pre-or post emergent, contact or systemic, selective or non-selective, and the pros and cons of each type. No single product will do the entire job of controlling all weeds.

  • Concern Weed Preventer Plus is made from corn gluten meal. This natural pre-emergent product both inhibits weed seed germination and supplies some nutrition to the soil (8-2-4) as it breaks down. (No label required)

  • Lebanon Seaboard’s Preen Garden Weed Preventer is a non-selective pre-emergent with the active ingredient triuralin. When applied as directed, it reportedly prevents most weeds from germinating in flower and vegetable gardens, in ground covers and around trees and shrubs. (Labeled Caution)

  • Clove oil is the active ingredient in Matran 2 from Bioganic® Crop Protection. This post-emergent herbicide is OMRI listed. (No label required)

  • Post-emergent QuikPro Dry Herbicide by Monsanto combines quick action with complete control, roots and all by mixing Roundup Pro (glyphosate) and diquat dibromide. Results are visible in as little as 24 hours. (Labeled Caution)

  • A non-selective herbicide that claims results that are usually visible within minutes after treatment is Scythe composed of pelargonic acid and related fatty acids. From Dow AgroScience, this material quickly penetrates green plant tissue and disrupts the cell membrane tissue. (Labeled Warning)

  • Another Monsanto product, Grass Getter, containing the active ingredient sethoxydim, is a post-emergent selective systemic grass killer that eliminates weedy grasses growing in and around planter beds, landscapes, and individual shrubs and trees. (Labeled Warning)
  • Safety should always be a priority when using an herbicide, both for people, pets and other garden creatures as well as other plants. Many ornamental plants are extraordinarily sensitive to broad-leaf weed killers and even the slightest amount of drift can cause stunted, twisted, cupped, curled, chlorotic foliage and even death to your plants. Damage from the popular non-selective herbicide glyphosate (Roundup) is commonly mistaken for disease or insect damage, and symptoms may not appear until the season following accidental exposure.

    Most weeds can be managed effectively by a combination of cultural and physical methods. If you choose to use chemicals, keep in mind that what you use in your landscape affects our rivers and oceans!

    Photo of bindweed is by AtWaG from and photo of dandelion is by Joan Goff. Both are used with permission. .

    Author’s disclaimer: Inclusion of a product in this series of articles does not constitute endorsement either by the author or the Marin Rose Society. Products are included for informational and descriptive purposes only.

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    Last Modified: 08/06/2013