Preventing Winter Injury

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The cold spell we had in mid-November was a good wake-up call that winter is on its way.  The question is “Are your plants ready?”  In most cases, the answer is “yes.”  Plants that evolved in the mid-Atlantic are prepared for winter by dropping their leaves or dying back to the ground completely, in the case of herbaceous perennials.  Needle evergreens have evolved narrow leaves with coatings that prevent moisture loss in the winter to help them survive.  The real problem is with broad leaved evergreens.  In a recent talk at the Delaware Ornamentals and Turf Workshop in Hockessin, DE, Jason Veil, curatorial intern at the University of Delaware Botanic Gardens, pointed out that of the 50+ broadleaved evergreens we commonly plant in Delaware, only 4 are native.  Very few broadleaved evergreens have evolved to handle our weather.

When we think about winter injury, there are a few factors in play.  First is the genetics of the plant.  It is important to know where the plant evolved.  Red maples grow from Florida to Canada.  Seeds from Florida red maples may not be hardy in northern states.   Most cultivars are selected for their ornamental characteristics, but environmental characteristics, such as cold tolerance, moisture tolerance etc. are even more important for planting success.

With broad leaved evergreens, the most common winter injury is leaf scorch–dead areas on the leaves.  This is caused by water loss during the winter.  Moisture is lost from the leaves, the wind blows the moisture away from the leaf surface and the leaf loses more moisture. Wind can’t be changed, but you can locate plants to avoid prevailing winds when planting broadleaved evergreens.  Excess sunlight is also a problem.  The sun can warm up the leaf, tricking the plant into losing more water.  So, plant broadleaved areas in spots that are protected from the wind and winter sun.  Since moisture loss is the major cause of winter injury in broadleaved evergreens, fall rains are important to build soil moisture. When you complain about that cold, wet day; remember how good it is for our plants.  If we have a dry fall, it may be necessary to water tender or newly established plants during the fall.  Fortunately, this fall we’ve had plenty of rain.

In Delaware, plants acclimate to the cold weather by “hardening off” in response to shorter days and colder fall temperatures.  Acclimation is a slow, steady process.  After a 2-month chilling period has been satisfied, deacclimation can occur pretty quickly in spring.  If we get some unseasonably warm weather in late February, plants can break dormancy before our cold weather is really over.  We’ve all seen cherries or magnolias start to bloom early and then get damaged by normal cold weather that follows. Loss of flowering is a nuisance, but deaclimation can cause even more severe injury when we get a warm spell in late winter.

Not all plant parts have equal cold tolerance.  Stem tissue is the most tolerant part of the plant.  Vegetative buds are next because the plant needs these buds to grow.  Flower buds are less cold tolerant; we want flowers but they aren’t as necessary for plant survival.   Interestingly, while they are critical to plant survival, roots are least cold tolerant because they are normally buffered by the soil.  Plants in above-ground containers are not as cold hardy as that same plant would be in the ground.

For winter hardiness, avoid top growth and promote root growth in the late summer and fall.  Avoid pruning and fertilization that would push new, tender growth.  Avoid planting perennials in the fall when there isn’t enough growing season left for them to establish a healthy root system before they have to tolerate the alternate freezing and thawing that occurs during a Delaware winter.  Evergreens don’t grow roots in the fall, so it is best to wait until spring to plant evergreens.

Salt is another important factor in winter injury.  Plants close to salted roads or sidewalks get the double whammy of cold temperature and salt injury.  For those locations, pick salt tolerant plants, like groundsel bush, eastern red cedar, bayberry and any other plant that grows well at the beach.

So, what can you do to prevent or reduce winter injury?  Start by selecting cold tolerant or salt tolerant plants.  Place those plants to avoid winter sun and wind.  Consider protecting broadleaved evergreens by planting in shaded locations, such as the north side of a building. Avoid late season fertilization and pruning and fall planting of evergreens.  Irrigate during dry spells in fall or before cold snaps.  Apply mulch to young or tender plants to help protect roots   Consider placing evergreen boughs over small tender plants for winter protection.  Some people wrap their evergreens in burlap to protect them from winter injury.  I have to admit that doesn’t make sense to me.  If you planted an evergreen, you chose it because it stays green all winter, why would you cover it up?  It is best to select plants that tolerate our weather conditions.  If you “push the envelope” as many gardeners so, be prepared to replace tender plants after a tough winter.  Who knows what the winter of 2014/2015 will bring.  We can only wait and see.

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Meadow responses

I received a lot of responses to my meadow column in the News Journal.  Here is one of the responses with my answers:

I read your article “Would a meadow a home work for you” in The News Journal, dated Saturday 7/26 suggesting I could start a fairly large “Meadow” by not cutting your front lawn and let nature “seed”, transform, the lawn area into a meadow.

I like the benefits of this concept eg: reducing the costs of cutting the grass, less watering, chemicals, and the increased rain water saturation to the and so, and I am interested but, I have a few questions before proceeding;

1. “won’t the lawn just turn into a weed patch of crabgrass, thistle, plantain, etc. when I stop cutting my grass”?

2. “what will prevent the weeds from crowding out the grasses and flowers mentioned in the article”?

3. “how can I control the spread of the weed seeds to my neighbors”?

4. “do you know if a “meadow” affects the value of my home considering right now all of my neighbors have lawns?

Great questions.  What the “lawn” becomes is highly dependent on what is currently in the lawn and the plants nearby.  If you currently have a vigorous stand of cool season turf, you will just get a taller stand of cool season turf.  Crabgrass is not a problem in a meadow, because the seed needs light to germinate.  Unless, you have many open patches in your lawn currently, the taller grass pretty much excludes light from reaching the soil and crabgrass will not grow.  In fact, crabgrass is less of a problem in a meadow than in a mown lawn.  Thistle could be a problem if you have it nearby.  It would need to be treated with an herbicide to get it under control.  Lontrel is recommended for use on Canada thistle. Plantain would be a relatively desirable component of a meadow. Its seed heads are interesting and it isn’t a problem plant.

Grasses are fairly competitive, so once you have a good stand in place they will do a good job of competing with incoming weeds.  I guess that also depends on what you define as a weed.  Many lawn weeds are not really weeds in a meadow.  Woody plants can be controlled in a meadow by mowing once or twice a year.

If the meadow becomes more diverse with age, which it will naturally do, there may be seeds that your neighbor would define as weeds.  But, there are probably natural areas, roadsides etc. that are already contributing weed seeds to your neighbor’s property.  You won’t be increasing that dramatically by having a meadow.

If you want a really great meadow that is comprised of warm season grasses and a few desirable perennials, it is best to seed the meadow with the plants you want.  Eventually warm season grasses will probably come into the meadow on their own.  Switchgrass (Panicum virgatum) grows extremely well in southern Delaware and may become a component of your meadow over time.  Or you could seed it into the lawn and jump start the process.

 

 

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Does a meadow work for you?

When I teach lawn management, the first point I make to my students is the lawn is so important its location must be selected first when you are designing a new landscape.  Decide where you want to play, gather and circulate—that should be lawn.  The rest of your landscape should be something else.  What else, you say?  You really have three choices: traditional landscape beds, forest or meadow.  Traditional landscape beds provide lots of interest and beauty in a garden but they can be costly to install and take a lot of time to maintain.  Most landscapes will have some traditional landscape beds.  Using mulch to reduce weeds and locating plants to be the tree canopy, shrub layer and groundcover make landscape beds more manageable.  Using native plants attracts native wildlife.  Starting small and allowing plants to grow together will reduce the initial cost and allow plants to establish more easily.

The second option is a forest or woodland.  Most people think they don’t have a large enough property for a forest, but you can have a small tree grove (i.e. forest) on very little land.  And it doesn’t have to cost anything.  At the University of Delaware Botanic Garden we let a small area of what used to be a golf course become a forest over the course of about 15 years.  The trees (red maple, sweet gum, black cherry, birch, tulip poplar, oak) were all planted by the birds, squirrels and wind.  The only maintenance involved was removing exotic invasive species that might have taken over the forest if we had allowed them.  So, if you have 10 years, stop mowing and eventually you will have a forest.  If you want to jump start the process, plant small trees, woodland shrubs (i.e. spicebush, viburnum, witchhazel) and forest ground cover (ferns, wood asters, celandine poppy).

Option three is the least expensive but also least understood landscape—a meadow.  Fortunately, Longwood Gardens is attempting to change our perception of a meadow.  Visit Longwood Gardens’ meadow–just opened to the public this June. It is 86 acres and contains 3 miles of walking trails.  Obviously larger than a typical residential meadow, it shows the visitor various components of meadow that could be incorporated into a home landscape.  The back bone of the meadow is warm season grasses.  Indiangrass, switchgrass, prairie dropseed and little bluestem are a few of the grasses native to our region.  Throughout the meadow, you will see blooming perennials like butterfly weed and black-eyed Susan.  At key nodes in the meadow, such as path intersections, bridges, benches and other structures, you will find more flowering perennials planted in masses.  The vistas are wonderful but the details are also charming.   One of the most important parts of the meadow is the path systems.  Paths provide access to a meadow and also show the meadow is being managed.

How can you incorporate a meadow into your home landscape?  Many people have large front lawns that are used for nothing other than taking a few hours weekend time to mow.  Keep a small area of maintained lawn around the house and let the rest of the lawn become a meadow.  Be sure to mow the edges routinely and if the yard is large enough, mow a curving path through the meadow.  It could be your back or side yard isn’t serving an important function and could become a meadow, reducing the time spent mowing, helping water infiltrate into your soil, providing a home for wildlife (birds and butterflies) and providing a different and desirable aesthetic to your home.  The least expensive way to start a meadow is to simply stop mowing.  The plants that come in will depend on your soil, moisture available and surrounding area.  If you want to jump start the process you can seed a meadow (for more information on seeding a meadow refer to this brochure:  http://extension.udel.edu/lawngarden/files/2012/06/live_eco_final.pdf).  Another great meadow example can be found at the Mt. Cuba Center.  Start to explore the possibility of having your own meadow and spend your weekends admiring the birds instead of cutting the grass.

Residential landscape in Delaware with meadow as a front lawn rather than mown turf.

Residential landscape in Delaware with meadow as a front lawn rather than mown turf.

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Summer garden tasks

We have had a fantastic spring for planting.  Frequent rains have provided regular water to anything you planted this spring.  It is about time to wrap up planting for the season.  Of course, you can plant all summer but you will have to be much more vigilant about watering newly planted trees, shrubs and perennials as the weather gets warmer and the rainfall less frequent (probably if we are going to have a normal Delaware summer).  If the weather gets really dry, you will need to water most of the plants you put in this spring.  Plants shouldn’t be considered fully established until they have gone through at least one complete growing season.  Large trees may take several years to become fully established.   Consider using a gator bag on newly planted trees.  Fill up the bag with a hose and the water will trickle out slowly allowing the soil to absorb all the water and making it available to the tree roots.  The same thing can be accomplished with a five gallon bucket that has a few holes punched in the bottom.  You can also water using a hose set at trickle, but that takes much more time and effort to keep moving the hose once the soil has become saturated.  Do not apply water faster than what your soil can absorb.  Water that runs off is wasted and can cause erosion and particulate pollution in nearby waterways.

With the bulk of your planting completed, it is time to turn your gardening attention to taking care of your plants.  Early summer is the time to prune spring flowering shrubs.  Always cut branches back to another branch or bud, never leaving a branch stump.  Remove the longest branches to reduce the size of your shrubs but maintain their natural form.  As perennials finish blooming, remove spent flowers to conserve the plant’s resources. Some perennials and shrubs will even re-bloom if cut back after flowering and before seed heads develop. But, if you want to encourage seeding to spread a ground cover or plant you want to fill into a larger space, then leave seed heads on and allow seeds to mature.  You might also want to leave seed heads to feed birds.  Gold finches love cup plant (Silphium perfoliatum) seeds, but I am always torn about leaving seeds because this plant seeds into the garden prolifically. Cut back fall-blooming plants, like mums and asters, now to encourage a compact habit when they bloom in August to October.

If you are managing a meadow, you may want to cut the meadow back now (mid to late June) to keep grasses from flopping later in the season.  We have had a wet spring, so grasses will be at the taller end of their normal range and may flop unless they are cut back now.  If you are cutting back your meadow, mow it to a height of 6-8 inches.  It will look sloppy for a few days, but the grasses and perennials in the meadow will quickly regrow and your meadow will be dense and lush again soon.  You should be mowing paths through your meadow to provide access and a “cue of care.”  You can mow the path on the same schedule as the rest of your lawn (approximately weekly) and mow one mower width on each side of the path every several weeks.  That will also help to keep the meadow looking neat and tidy and keep the path clear of flopping grasses.

This cup plant (tall yellow flower on the right) will feed gold finches but it will also seed into the garden, so be careful.

This cup plant (tall yellow flower on the right) will feed gold finches but it will also seed into the garden, so be careful.

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Weeding—does it ever end?

Weeding is one of those gardening tasks that some people find peaceful and enjoyable and others HATE!  Weeding is a component of gardening but it doesn’t have to consume all your gardening time.  Here are some strategies to help control weeds:

Use groundcover in your landscape beds to compete with weeds.  Most landscapes should have three layers—tree layer, shrub layer and groundcover.  When landscape designers, draw landscape plans, they tend to draw in large circles for the trees and smaller shrub circles, but often neglect to specify plants below the shrubs to cover the ground.  Few shrubs branch to the ground completely and therefore require a layer of plants below them to prevent weeds from growing in the bed.  The University of Delaware gets a lot of mileage from lilyturf (Liriope spicata) as a tough groundcover that out competes most weeds.  But, if you want more variety, you can try lamb’s ears (Stachys byzantina), bugleweed (Ajuga reptans), sweet woodruff (Galium odoratum), Allegheny pachysandra (Pachysandra procumbens)—a great native that takes a little while to establish but fills in thickly once it gets going, Christmas fern (Polystichum aristicoides) or barrenwort  (Epimedium sp.)—a great plant for dry shade.   Also consider planting perennials to fill in spaces rather than just shrubs.  Catmint (Nepeta  x faassenii ‘Walker’s Low’) is a great perennial that grows densely and out competes most weeds.  It is blooming now in Delaware gardens.  If you have a large space to fill, you might try mountain mint (Pycnanthemum muticum).  It is a vigorous grower and could become a problem in a small garden but its mid-summer flowers last until September in the form of silvery bracts.  It is also one of the best nectar sources for butterflies and bees so it is great to include in a pollinator garden.

Another weed control strategy is to cover the landscape bed with mulch.  Mulch will prevent light from reaching the soil, so few annual weeds are able to germinate.  You can generate your own mulch with composted yard waste and ground up leaves.  You can also buy leaf mulch or hardwood bark mulch.  Use mulch as a temporary feature, until your plants fill in or at the edges of beds to differentiate the landscape bed from the lawn.

Herbicides can be used carefully to control weeds as well.  Pre-emergent herbicides are used to control annual weeds before they emerge, by setting up an herbicide barrier in the soil.  It is a little late to apply a pre-emergent product this year, but something to consider for landscape beds next year.  Selective post-emergent herbicides can be used to control grass in landscape beds or broad-leaved weeds in lawns.  You can also use a glyphosate product (Roundup is one example) to spot spray weeds, but be careful because glyphosate kills most green plant tissue it touches.  It is easy to get spray drift and damage desirable plants.

Barrenwort (Epimedium sp.) in flower at the Delaware Center for Horticulture.

Barrenwort (Epimedium sp.) in flower at the Delaware Center for Horticulture.

Allegheny spurge (Pachysandra procumbens) on UD's campus.

Allegheny spurge (Pachysandra procumbens) on UD’s campus.

Finally, readjust your attitude about weeding.  Bring a cushion and a glass of iced tea outdoors with you.  Put on a good pair of gardening gloves.  Have a weed bucket nearby and spend a little time each weekend or evening relaxing in your garden and pulling up a few weeds.

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Hydrangeas – Star of the Summer Garden

Summer?  Wait, we are just starting to enjoy spring weather.  But, now is the time to buy and plant trees, shrubs and perennials to enjoy this summer.  Do big blue and pink globes of hydrangea flowers remind you of your grandmother’s garden?  If so, come and get a dose of nostalgia or enjoy lots of trendy new hydrangeas .  Hydrangea is the featured plant of this year’s UDBG sale and is certainly a trendy plant in the industry.  This genus includes a wide range of plants from vines to large shrubs.

Bigleaf hydrangea  (Hydrangea macrophylla) is the old fashioned plant most of us remember from Grandma’s garden.  This species produces large balls of sterile flowers that are either pink in basic to neutral soils or blue in acidic soils.  The added fun of changing soil pH to change the flower color makes this plant unique.  There are also lacecap varieties in this group that have a ring of sterile flowers around a center of fertile flowers, looking like a lacecap (duh!).

Panicle hydrangea (Hydrangea paniculata) is another old time favorite. The flower head forms a large cone of sterile flowers with lots of fertile flowers in the interior.  Most are white, fading to pink but some new cultivars fade to pink more quickly and retain the pink color longer, even as dried flowers.  Panicle hydrangeas bloom on new wood, so they should be pruned in late winter to early spring, for the best blooms.

If you want a native hydrangea, look for smooth hydrangea (Hydrangea arborescens) or oakleaf hydrangea (Hydrangea quercifolia).  Smooth hydrangea is not super showy as the straight species, but several showy cultivars are available.  Oakleaf hydrangea is a popular coarse-textured plant with exfoliating bark and large globose flowers.  Oakleaf hydrangea flowers are white, fading to pink and often hang on the plant all winter, providing interest and structure to the winter garden.  Leaves in this species turn a beautiful burgundy color in the fall.

If vines are your thing, there is even a hydrangea vine (Hydrangea anomola spp. petiolaris) that adheres to rough surfaces such as masonry and tree bark.  This vine has numerous white flat-topped flower clusters ringed by white sterile flowers in the summer.  Use it on a wall next to a walkway where there isn’t room for a shrub or tree.

Hydrangea flowers are great for cutting and drying.  Plants tolerate a range of conditions from full sun to full shade depending on the species and cultivar.  Many new cultivars have been selected for smaller sized plants with different flower colors and shapes.  The UDBG Plant Sale was the last weekend in April but you can still access the catalog for a complete listing and description of lots of great hydrangeas as well as many other plants. Look at the online plant sale catalog by visiting this URL. (http://ag.udel.edu/udbg/events/documents/UDBGCat14_WEB.pdf).

Spigelia marilandica and Hydrangea quercifolia – Oakleaf hydrangea with a native perennial, Indian pink, in the University of Delaware Botanic Garden.

Spigelia marilandica and Hydrangea quercifolia – Oakleaf hydrangea with a native perennial, Indian pink, in the University of Delaware Botanic Garden.

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