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Friday, April 29, 2016

Wise Watering Practices for Newly Planted Trees and Shrubs

Kathy Zuzek, Extension Educator

It is prime time for planting trees and shrubs in Minnesota. If planting is on your list of spring chores,
remember that proper watering is the most important practice to ensure survival and establishment of
your woody plants. No matter what planting stock you choose - bare root, containerized, balled and burlapped, or tree spaded – your new tree or shrub has a smaller root system than an in-ground, established plant. Frequent watering allows an under-sized root system to supply all the water needed by the plant while the root system expands and grows to a normal size. Under-watering and over-watering are both detrimental to plant health so it is important to know when to water, where to water, and how much water to apply. Wise watering practices for newly planted trees and shrubs can be found here.

Thursday, April 28, 2016

Boxwood leafminer: A rare insect in Minnesota

Jeff Hahn, Extension Entomologist

Boxwood is a shrub or small tree that usually grows well up to hardiness zone 5. They are marginally hardy in Minnesota (hardiness zones 4 and 3). Despite that, boxwood can be found occasionally here in the landscape. Where boxwood is commonly grown in landscapes in states further south, the most serious insect pest is boxwood leafminer. In the upper Midwest this insect is rare. A resident in a Minneapolis suburb recently reported the presence of this insect in her boxwood.

As an adult, boxwood leafminer is a small delicate orangish mosquito-like fly belonging to the gall
Boxwood leafminers: The blistering damage by the leafminers
can be seen in the top leaf while damage and larvae are seen
in the bottom leaves.  Photo: John A. Weidhass.
midge family (Cecidomyiidae). This insect spends the winter as a larva inside boxwood leaves. It becomes active when the weather warms in the spring and eventually pupates and emerges as an adult. Adults lay eggs inside the boxwood leaves which hatch later in the summer where they remain through the winter. There is just one generation a year.

The feeding of the larvae causes irregularly shaped swellings in the leaves. These damaged areas yellow at first and eventually turn brown. Despite this appearance, this feeding is generally just cosmetic, just affecting the plant’s appearance. In most cases, it is best to tolerate boxwood leafminer feeding as it is likely causing no lasting injury to plant health. Keep in mind that this is a rare insect in Minnesota and not widespread.

It is not clear where this insect occurs in Minnesota. If you live in Minnesota and have a boxwood, I would be interested to hear whether you have encountered this insect or not. Contact me at

Wednesday, April 27, 2016

Water Wisely: Grapes in the home garden

'King of the North' grapes
Photo: Julie Weisenhorn
By Matthew Clark, Assistant Professor
Grape Breeding and Enology
Department of Horticultural Science.

Grapes are a welcomed addition to home gardens. Successful grape breeding by universities and grape growers has resulted in a very good selection of varieties that perform well in our northern landscapes. These fruits can be grown for wine, jams and jellies, and as table grapes for fresh eating. University of Minnesota Grape Varieties

Some growers may make claims that a stressed grape plant will produce better wine. In reality, grapes need to have adequate water to enable systems like photosynthesis, evaporative cooling, and nutrient transport to work properly. Common symptoms of drought stress in grapes wilting leaves, change in leaf angle (away from the sun), and shriveling fruit. Drought stressed plants are less likely to survive Minnesota winters.  Winter injury itself can cause symptoms of drought stress and allow vines to become infected with crown gall.  Careful observation of trunks and canes of wilted plants will help to identify if the symptoms are caused by vascular damage, disease, or drought.

Soak bare root vines
3-4 hours before planting
Photo: Julie Weisenhorn
Grapes can be purchased as bare-root stock or in pots. Bare-root plants are dormant and have an   When watering the young vines, the root zone should be well saturated. Applying 5 gallons of water over a 3 x 3 foot area is a good estimate for 1 inch of water.
established root system that is in balance with the shoot. They must be soaked in water for 3-4 hours prior to planting, but will be less vulnerable to drought stress at planting than potted vines. Plants grown in pots require regular watering until the roots become established and the leaves have acclimated to growing outdoors. It will be worthwhile to monitor these plants daily to ensure they do not suffer drought stress. Young grape vines need regular watering to ensure successful establishment especially at the time of planting and the following two years. Older vines seldom need any watering unless on sandy or other very well drained soils.

According to Growing Grapes for Home Use, grapes are best planted in spring and grown in well-drained soil. The amount of organic matter in the soil may influence the growth and vigor of vines by providing access to additional nutrients.  Dig a hole large enough to spread out the root system. Cover the roots completely with soil. Create a slight depression around each vine. This will allow water to pool and soak into the soil, saturating the root area and preventing run-off.  Mulching is not recommended for grapes because mulch will moderate the soil temperature, often keeping it cooler in warmer months, and grape vines grow best in warmer soil.

Young grapes require about ½ to 1 inch of water per week, depending on rainfall, for the first two years during the growing season. By the end of the second growing season, a trunk should be established and your vine is likely to not need additional watering intervention unless specific soil conditions (sandy, well drained) or prolonged drought dictate the need. Apply water only to the root zone. Avoid getting grape foliage wet as this can encourage many grape diseases. Reduce watering young vines going in the fall to encourage the plant to harden off its canes to prepare for winter.

Managing weeds near grapevines is critical as weeds compete for water and nutrients as well as harbor potential insect and vertebrate pests. Weeds can be managed by hand-pulling, cultivation (hoeing) or through the use of well-timed herbicide applications. Cultivation and herbicide application before planting is most effective.  Combining a pre-emergent herbicide and a broad-spectrum herbicide like glyphosate before planting, and while plants are dormant in subsequent years can be a very effective strategy.  Make sure to not apply contact herbicides after the buds begin to grow as grapes are very sensitive and easily damaged by herbicides. Grow tubes can help protect the young, and sensitive vines and are a great tool when is establishing a planting.  They can even minimize damage from deer.

Additional Extension resources on grapes:

Thursday, April 21, 2016

Weed management: creeping charlie

Julie Weisenhorn and Sam Bauer, Extension educators

Treating aggressive perennial weeds requires proper timing, an effective product and cultural
practices to help deter re-establishment. Creeping Charlie (Glechoma hederacea) is consistently a problem weed though some homeowners have come to tolerate it because it attracts and provides food for pollinators (one of its few redeeming qualities).

Creeping charlie in bloom
Also called ground ivy, creeping charlie is part of the Mint family. Like all mints, it spreads on top of the soil via stolons (surface roots) and will regrow from very small pieces of vegetation left behind in the soil after removal. It is a very adaptable plant and grows well in moist soil in part shade / full shade sites. Creeping charlie can be found where lawn grass is thin and not very robust. This may be in compacted soils, shady locations, and weedy sites. Therefore, treating with an appropriate product, maintaining a healthy lawn, utilizing shade tolerant grasses, and choosing alternative ground covers in areas not suitable for growing lawn grasses will help manage weeds including creeping charlie. 

Best cultural practices are recommended to encourage healthy growth and vigor of lawn grasses. Proper selection of grass varieties for the site, fertilization and watering practices that encourage deeply rooted plants are important to a healthy lawn that can out-compete weeds. 

Most lawns are comprised Kentucky bluegrass and perennial ryegrass and require full sun, proper nutrition, and non-compacted soils for optimal growth. A soil test can provide recommendations for soil health and fertilizer. As shade increases, it becomes less and less favorable for sustaining a lawn in this area, and more favorable for weeds like creeping Charlie. Pruning to increase sunlight and aeration may be options for improving growing conditions; however, if the area is too shady, give up on trying to grow grass in this area and consider planting other ground covers or a shade garden of perennial flowers. 

Creeping charlie and dandelions are
both perennials weeds in turf
Timing of herbicide treatment is key to successful control of perennial weeds like creeping charlie. As always, read and follow all instructions and guidelines on the label of any product, synthetic or organic, including proper clean up and storage. Note that herbicides are only effective in managing weeds if applied properly. The herbicide label is the law and misuse constitutes illegal application. Autumn is the best time of year for systemic herbicide applications when creeping charlie is actively taking up nutrients from the soil to sustain the plant through the winter. Spring is a second option when the plant is actively growing.

Some considerations for choosing an herbicide:

  • If you have a large area of creeping charlie or if your lawn is more than 50% creeping charlie, you may want to consider killing off the entire area with glyphosate (the active ingredient in the non-selective herbicide Round-Up®) and re-seeding. Note this product kills all plants including lawn grasses. Depending on the product formula, re-seeding can occur within a few days after application. People and pets may re-enter the area when dry.
  • If you want to treat small areas where creeping charlie is growing in lawn grasses, you can use a a selective herbicide like 2,4-D, Dicamba or triclopyr, or combinations of these products. Triclopyr will be the most effective option for creeping Charlie. These are systemic, selective broadleaf herbicides. They are taken up by the plant and kill the entire plant from roots to flowers. Note they do not kill lawn grasses if applied properly. These products are effective and usually require only 2-3 applications per year depending on proper use and timing.
  • Chelated iron burns creeping charlie foliage and its stolons. A maximum of four applications may be applied annually. Lawn grasses may show some burning on the blades, but will recover. They also will turn a deep green due to the absorption of iron. Because of this, chelated iron should not be used for spot treatments as it will result in deep green spots throughout the lawn. Treated areas may be re-seeded the next day, and people and pets may re-enter the area when dry. Note that chelated iron can be expensive, and may stain equipment, sidewalks, driveways, etc. Here is a publication from the University of Maryland with more information

In the past, borax (boron) was a product recommended for eradicating creeping charlie. However, research has shown that the addition of boron to soil, even in very small amounts, can create an unfavorable growing environment, and make it difficult to re-establish lawn grass. Also, this is an illegal application.  Any product used in this fashion must be specifically labeled for the weed you are trying to control.  Therefore, borax it is no longer recommended for eradication of creeping charlie.

Going forward, regular and well-timed cultural lawn care practices will help keep weeds like creeping charlie managed and turfgrass healthy. The Upper Midwest Lawn Care calendar is a good tool for helping time applications of fertilizer and pre and post-emergent herbicides and when to perform tasks like aeration to reduce compaction. For more on healthy lawns:

Round-Up® is a trademark of Monsanto Corporation.

Garden offenders: get a jump on four common problem plants

Julie Weisenhorn, Extension educator

Typically people contact Extension with the question "How can I get get rid of  __________?" (fill in with a troublesome plant). Unfortunately, these offenders are well-established by the time we usually get this call. So here are four of the most common problem plants and what they look like now in their emerging stage, so you can get a jump on getting them out of your yard and garden!

Buckthorn in springtime
Buckthorn (Rhamnus cathartica)
Public enemy #1, buckthorn was introduced as a hedge plant. buckthorn was a favorite of urban homeowners for its interesting cherry-like bark, tolerance to many growing conditions and its receptiveness to pruning. Today, common or European buckthorn as well as glossy buckthorn (Frangula alnus Mill.)  are listed on the Minnesota Department of Agriculture Restricted Noxious Weed List. Buckthorn is leafing out right now and can be easily spotted by its silvery-gray park with white lenticels, bright green, rounded young leaves and the sharp thorn on the ends of branches. Guidelines for removal can be found on the Minnesota Department of Natural Resources buckthorn webpage.
Silvery buckthorn bark
with white lenticels

Thorn on young buckthorn

Garlic mustard (Alliaria petiolata)
Also listed on the Minnesota Department of Agriculture Restricted Noxious Weed List, this biennial
Young garlic mustard plant
 plant is stealthy. Its cute, tidy rosette of scalloped leaves can sometimes be mistaken for more desirable ornamentals like hollyhocks. Beginning gardeners or gardeners new to the area may be afraid to remove it.  An easy identifying feature: garlic-scented leaves. (Plan to throw away your gloves after pulling these plants). As a biennial, garlic mustard puts its energy into leaves and roots the first season, and blooms the second season. If left alone, the small clusters of white flowers result in hundreds of tiny seeds, making is a prolific invader of our woodlands. This is one plant that warrants chemical spot treatments.
For more: Minnesota Department of Natural Resources garlic mustard page.

Creeping charlie (Glechoma hederacea)
Early blooming creeping charlie
Not a Smart Gardens radio show goes by without a creeping charlie question - even in the winter! A member of Mint family and like other mints, it spreads by means of stolons (surface roots). Though not a registered noxious weed the Minnesota Department of Agriculture, it is considered invasive by the Minnesota Department of Natural Resources and can be a tough plant to eliminate once it has become established though some homeowners have come to tolerate it because it attracts and provides food for pollinators (one of its few redeeming qualities). It is a very adaptable plant and grows well in moist soil in part shade / full shade sites where lawn grass is thin and not very robust. This may be in compacted soils, shady locations, and weedy sites. Therefore, treating with an appropriate product, maintaining a healthy lawn, utilizing shade tolerant grasses, and choosing alternative ground covers in areas not suitable for growing lawn grasses will help manage weeds including creeping charlie. More on creeping charlie

Creeping bellflower (Campanula rapunculoides)
Creeping bellflower emerges early
Creeping bellflower forms a mat
Campanula cultivars are favorite perennials of gardeners, and Campanula rotundifolia, harebell, is a Minnesota native wildflower and a tough plant that grows in rocky, dry soil. However, its European cousin, the creeping bellflower (C. rapunculoides) is an aggressive plant and not so well-liked. Creeping bellflower forms mats of thick, tuber-like rhizomatous roots. It is a prolific seeder and quickly outcompetes more desirable plants for moisture and nutrients. This plant leafs out early, making it easy to spot treat with a broadleaf herbicide and easier to remove by hand while desirable plants are still emerging. For more details: Minnesota Wildflowers,
Wisconsin Department of Natural Resources

Tuesday, April 19, 2016

Soil temperatures needed for germination

By Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension - Stearns & Benton Counties

ST. CLOUD, Minn. - Many gardeners were ready to get a jump start on their gardens when it was so warm back in early March. Although the frost is out early this year, soils need to reach a specific temperature in order for seeds to germinate. Click here for a list of common vegetables and the minimum and optimal soil temperatures for seed germination ...

Friday, April 15, 2016

Do your trees and shrubs need fertilizing this spring?

Kathy Zuzek

The most beneficial time to fertilize trees and shrubs is from early spring when soil becomes workable until the time in April or early May when woody plants move into active growth. Fertilizing at this time provides woody plants with nutrients just as they put on their main flush of growth during spring.
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