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Thursday, April 16, 2015

How to find help with a home landscape

Home owners often ask Extension how to find a student, a Master
Gardener, or an industry professional to help them with a home landscaping project or garden design.  They wonder if students need projects, if Master Gardeners can do this kind of activity for their volunteer hours or how to choose a landscape professional.

Landscape professionals typically have a degree in landscape design or a related area, and /or are licensed as a landscape architect. Some garden centers offer full service landscape design, implementation and maintenance services. Homeowners can also find firms by searching the Minnesota Nursery and Landscape Association website. Use the search function to find the type of help you are looking for in your geographical location; for example, "landscape designer St. Paul, MN". Word-of-mouth is also a very good way to find a landscape professional. When you see a landscape you love, ask the homeowner for a recommendation.   

To reach students looking for seasonal work or alumni in the landscape business, post a job description on GoldPass: Job, Internship and Volunteer Listings. GoldPASS is the U of M's online database to help connect students and alumni with employers, volunteer organizations, and internships across the country. Posting is free, easy to do, and open to anyone.

Homeowners may also choose to send a job description to the Extension Master Gardener program in your county. Master Gardeners are educated by University Extension, and volunteer by teaching the general public research-based horticulture information. While Master Gardeners are volunteers and are not allowed to accept payment or work on private properties as part of their volunteer hours, some are professional gardeners, designers or landscape architects by trade. A county program may have a website or newsletter for volunteers only where such job postings can be made available.

Thursday, April 9, 2015

Back to Bleach to Keep Pruning Tools Clean

M. Grabowski, UMN Extension

When pruning out a branch infected with a fungal or bacterial plant pathogen there is a risk that the pathogen will stick to the pruning tool and spread to other trees and shrubs that the tools is used on. This risk is very low during the winter months, as many plant pathogens are dormant along with the trees. Pruning cuts made during the growing season carry a much higher risk of transferring plant pathogens on pruning tools from one plant to another.

Leaves & blossoms killed by fire blight. M. Grabowski UMN
This spring gardeners should be extra careful when pruning crabapple, apple or mountain ash trees that suffered from fire blight last year. Fire blight is caused by the bacteria Erwinia amylovora. This bacterial plant pathogen survives Minnesota’s winter in branch infections called cankers and emerges in warm spring weather in a sticky liquid called bacterial ooze. The fire blight bacteria are easily spread on pruning tools.

To avoid this problem, pruning tools used on infected trees anytime after bud break should be sterilized between cuts. In 1991, a researcher named Beth Teviotdale published a study showing that the best solutions for sterilizing pruning tools were a 1:5 solution of Pine-sol, Lysol, or household bleach and water. Rubbing alcohol (70% isopropyl alcohol) killed some but not all of the bacterial pathogens on the blade.

Unfortunately although product names remain the same, the ingredients in the bottle may change. In fact the formulations of Pine-sol and Lysol have both changed significantly since 1991. New research is needed to determine if these new formulations are effective in sterilizing pruning tools. In the meantime, a 1:10 dilution of household bleach (5.2% sodium hypochlorite) in water remains the most effective solution to sterilize pruning tools. It can be applied as a spray or by dipping or soaking the blade in the solution.  Bleach can be corrosive to metal.

Monday, April 6, 2015

Q&A: Organic Lawn Care

Question: I have read the report on but still not sure what I need to do to get rid of weeds in my lawn naturally. We have not treated our lawn for a while and now gradually grass is being replaced by clover and other weeds. Any suggestions? We would like to avoid chemicals in our yard.

Answer: Thank you for your question. The goal: keep your lawn as healthy as possible through good cultural practices. This will enable it to out-compete weeds and tolerate the heat of the summer and winter cold. Here are some steps you can take to manage weeds in your lawn without chemicals. Note that these are considered "cultural methods" of management and must be ongoing to be continually effective.

  • Re-think your idea of a "perfect lawn". Accept some non-grass plants in your lawn. Dandelions and clover are good plants for bees as they provide early season pollen and nectar.
  • Raise your mower blade to 3". Longer grass blades keep plant crowns cool, moist and less stressed during summer heat. Mowing regularly also helps to manage weeds.
  • Depending on the size of a weedy area, digging out weeds by hand and re-seeding is sometimes your only option. It is an ongoing maintenance task. You may choose to eliminate areas of grass altogether and re-plant with shrubs, perennials, and trees.
  • Water grass deeply and infrequently. The top 5-6" of soil should be moist. This will cause grass roots to move deeper into the soil seeking the water. If you water a little at a time, the water only wets the top few inches of soil. This causes the grass roots to stay at the surface of the soil - where the water is - and thus are more likely to become stressed and dry during the heat of mid-summer.
  • Avoid trying to grow grass under trees. Instead, mulch these areas and plant hardy perennials like Hosta, Heuchera (coral bells), and native wildflowers. This approach eliminates thin grass that cannot out-compete weeds. It also eliminates potential damage to tree trunks and tree roots by lawn mowers and weed whips that can lead to tree health issues. Plantings under trees also look really lovely and provide interest in the landscape.
  • Fall is a good time to aerate your lawn. Aeration removes soil plugs from the ground, lessening compaction and creating a better environment for grass roots. Local equipment rental shops have aerators or you can hire a landscape maintenance company to aerate.
  • After aerating, over-seed your lawn with a soil / compost / seed mixture. In Minnesota, we grow cool season grasses. They are most actively growing in spring and fall. Choose grass seed that is suitable for your conditions (full sun, part sun, shade, etc.). You can purchase this at a local garden center. Note that high quality seed usually costs more. Ask for help in choosing a seed mixture(s) suited to your yard. Some stores can also mix seed for you.
Be sure to continue utilizing U of M Extension Garden resources and publications for gardening information.

Thursday, April 2, 2015

Spring Preemergent Applications for Crabgrass

Every year around this time I start receiving questions regarding when to apply preemergent herbicides for preventing crabgrass establishment in lawns.  Crabgrass germination is driven by soil temperatures and because of this we cannot rely on a calendar date to tell us when to apply our preemergent products.  The reality is, if we wait too long and miss the window of opportunity to apply crabgrass preventers, these products will not do much for control of crabgrass.  For this reason I like to rely on a couple of website resources that help to determine when to make these applications.  The first website that I like to use can be found here:  This is a site operated by Michigan State University and the model uses air temperature predictors to determine when to apply crabgrass preventers.  Simply select the tab "Crabgrass PRE", enter your zip code, and the map will be created.  Below is the current map for Minnesota.  As you can see, we are just getting into the time for optimum prevention of crabgrass with preemergent herbicides.  Based on the extended forecast calling for sub-50 degree air temperatures, we still have plenty of time to get these products down. For a more detailed explanation of how to utilize this website for crabgrass prevention, see this great post from Dr. Aaron Patton at Purdue University: 

The other website that I like to use is the University of Minnesota's Climatology Working Group Site: On this site you can look up weather information including soil temperatures for your specific location in the state.  For example, below is the current map for soil temperatures under sod in St. Paul at depths of 1, 5, 10, 20, and 50 cm.  Preemergent herbicides for crabgrass should be applied before soil temperatures are 55 degrees in the upper 1-2 inches for several days.

Now here's something else to think about.  Crabgrass preventers that include fertilizer, like Scott's Turf Builder with Halt's Crabgrass Preventer, can be convenient for both professional turfgrass managers and homeowners.  However, when using products that offer the convenience of a 2 in 1 (fertilizer with herbicide), it may be more difficult to identify an ideal timing for application.  By this I mean that the appropriate time for applying a crabgrass preventer may not coincide with the time to fertilize.  Typically we suggest to apply fertilizer to your lawn when it is actively growing in the spring from mid-May to early-June.  If the lawn isn't actively growing and quick release sources of fertilizer are used, there is a potential for these nutrients to be lost through leaching or runoff.  Crabgrass preventers should go down from mid-April to mid-May, which is often too early for fertilizing.  For these reasons, I suggest to use caution with these products and carefully consider when would be the appropriate time to make applications depending on where you are in the state.  Products containing slow release sources of nitrogen can be put down earlier than products with quick release sources.

For more information on preventing crabgrass, including identifying crabgrass and choosing herbicides, visit these great resources from Purdue University and Dr. Aaron Patton's Program:

Tuesday, March 31, 2015

Wasp queens not a sign of active nests

Jeffrey Hahn, Extension Entomologist

Seal openings that allowed hidden nests in voids last year
 Wasps have been active inside homes with the recent warm weather we have experienced. A question people ask is whether this indicates that a nest with live wasps is in their house. Fortunately, what people are seeing are overwintering queens that have randomly selected a given building last fall in which to overwinter. The old queen and all of the workers in the nests died last fall when freezing temperatures arrived. When it warms up during late winter and early spring, these new queens become active but usually become trapped accidentally inside homes and other buildings.

It is important to note that while wasps do not reuse old nests (an exception to this is European paper wasps), they can reuse spaces. If a person had a problem with a hidden nest, i.e. one that is in a wall void or other space within a building, now is a good time to seal the opening where the wasps were flying in and out. This will help prevent new queens from starting any new nests in the cavities.

This is also true for ground nesting wasps that were found on your property last year. Queens construct nests in old rodent burrows and similar sites. Now is a great time to fill in these entrances so new queens are not able to start new nests in those spaces.

As long as temperatures remain cool, wasps will be generally inactive. But on days with warm, sunny weather, wasps may be seen in your home. The only necessary control is to physically remove (or crush) them. You can also capture them and release them outdoors.

Friday, March 27, 2015

Finalize pruning for tree health

Black Knot on Prunus.
M. Grabowski, UMN Extension

As a general rule of thumb gardeners are told to prune out any diseased branches from trees and shrubs before the end of March. The biology behind this rule tells us that during cold winter weather, trees and the microorganisms that cause tree diseases are dormant. When the weather warms up, trees become active and so do their pathogens. Pruning cuts made in cold weather are less likely to become infected with the pathogen being pruned out or any other pathogen.

Fire blight canker on crabapple

In addition, many plant pathogens of trees and shrubs overwinter in infected branches. Common examples are black knot galls on Prunus spp. caused by the fungus Apiosporina morbosa,  fire blight cankers on crabapples, apples and mountain ash tress caused by the bacteria Erwinia amylovora and golden canker of pagoda dogwood.

Golden Canker on Pagoda Dogwood
Cankers and galls should be pruned out by making a pruning cut 6-8 inches below visible symptoms of the disease (cracked, swollen or discolored bark are common symptoms). This will ensure that all of the pathogen is removed from the tree and only healthy tissue remains. Infected branches can be burned, buried or brought to a municipal or commercial composting facility.

NOAA map for gardeners about climate normals - MN Weather Talk, March 27, 2015

USDA Plant Hardiness Map for Minnesota
Excerpt from MN Weather Talk by U of M Climatologist Mark Seely, March 27, 2015

NOAA - the National Oceanic and Atmospheric Administration - released a helpful guide for gardeners to use this spring which is a map depicting the new climate normals. Plant Hardiness Zones have clearly shifted geographically with the changing climate and NOAA scientists explain this in some detail at the web site in an article titled "Planting your spring garden? Consider climate's 'new normals.'" Read more

So when selecting plants for your garden, always choose plants that are listed for your hardiness zone. This indicates the plant has been trialed by the breeders and proven to survive and thrive in the zone listed. Not sure of your hardiness zone? Consult the USDA Plant Hardiness Zone Map.
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