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Guest Post: Preventing and Controlling Weeds

Monday, March 25, 2013 Leave a Comment

By Sarah Christian, Urban Gardens
Excluding the handful of people who find weeding cathartic, most of us would prefer to spend our time outside doing something other than weeding.  Yet whether we enjoy weeding or not, most find it a necessary chore.  There are two strategies for dealing with weeds.  One is to try to prevent or at least minimize weeds in your lawn and garden beds, the other is to remove and control weeds once they take up residence.
Prevention keeps weeds from occurring or increasing in your yard.  When installing lawn, make sure you purchase sod from local growers that grow weed-free sod or seed from local companies that sell nothing but seed and make sure the package label indicates that it is 100 percent weed-free.  Most retail seed mixtures will contain some weed seed.  Once your lawn is established, the best defense against weeds is a lawn that is healthy, dense and actively growing.  

Many weeds thrive in lawns where there is insufficient nitrogen because they need less nitrogen than grass.  Some of the weeds that like these conditions include white clover, black medic, dandelion and crabgrass. 

There are several factors in keeping your lawn healthy.  Water properly, in the late evening or early morning avoiding frequent shallow watering and using the frequency and duration recommendations of the Denver Water Board which will vary from month to month.   Mow bluegrass lawns to a minimum height of two to three inches.  Aerate in the spring and apply a pre-emergence herbicide.  The herbicide must be applied in March to early April before weeds emerge or the product will be ineffective.  Lastly, apply a nitrogen fertilizer.  October and November is the best time to fertilize.
In your garden beds, weeds can be minimized with weed barrier fabric and mulch which limits light required for annual weed growth. 
Weeds should be removed from your yard so they will not reoccur.  It’s important to know there are different control methods for different types of weeds as they all have different growth patterns, reproduction patterns, food storage and even root systems.  Hand weeding is effective with small annual weeds if done before flowering but it is generally not effective with perennial weeds because a large part of the root remains in the soil and quickly regenerates another top.  
Use chemicals only on individual weeds as liquid spot treatment is more effective and environmentally friendly than “weed and feed” type applications that are applied to the entire lawn.  When applying liquid chemicals to weeds with a sprayer, spray just until the foliage is moist.  Dry granular formulations should be applied to wet grass and weeds.  Use herbicides when temperatures are above 65 and not expected to rise above 85 degrees within 24 hours of application.  Spray weeds when there is little or no wind to minimize the danger of herbicide drift and avoid watering for 24 hours after application.  Broadleaf weed killer should be used for broadleaf weeds.  Roundup®  is an effective weed grass killer but it will kill both the weed grasses and lawn so it should be used only to spot-spray individual patches of undesirable grasses.    After weeds have been removed, you should re-seed or sod the empty space to prevent another weed infestation and any soil left exposed in garden beds should be remulched.  
In spite of our best efforts, some weeds will still occur.  Some species are very aggressive and can be resistant to the herbicides we use.  Perennial weeds are some of the most difficult to control but are most effectively controlled with a late summer/early fall herbicide application when they are green and actively growing.  Herbicide mixtures, containing three or four different herbicides, often provide better control of difficult weeds.  Identifying the type of weed is key to selecting the most effective herbicide product.

There are also some organic methods available such as corn gluten meal which can be used as an organic pre-emergent herbicide with fertilizer to suppress seed germination and help green up your lawn.  Vinegar can be used to kill weeds but will also kill lawn and require repeated applications.  Boiling water from a tea kettle will kill annual weeds and kill or control perennial weeds.  

“A man’s children and his garden both reflect the amount of weeding done during the growing season.” - Unknown

“Weed Management for Pros”,  by Dr. Tony Koski                                                                             CSU Extension.edu, No. 3.101:  “Control of Annual Grassy Weeds in Lawns”                        Plantalk Colorado, No. 1525:  “Controlling Broadleaf Weeds in Lawns”                                   Plantalk Colorado, No. 1530:  “Controlling Weedy Grasses in Lawns”

About Urban Gardens, Inc.:                                                                                                                                          Urban Gardens provides landscape design and consulting services to residential clients whose projects range from historic renovations to new subdivisions with a blank slate.   Sarah Christian owns and operates Urban Gardens in the internationally recognized Stapleton Development in Denver, Colorado.  She received her Masters degree in Landscape Architecture from the University of Colorado at Denver in 1995 and has worked in Colorado since that time.  She is licensed by the state of Colorado and is a member of the American Society of Landscape Architects.  You can visit her web page at www.urbangardensinc.com