Archives For Tim Johnson

Like you, the staff at the Chicago Botanic Garden has been tracking the recent rains. We know many of you are anxious to get planting done—it is spring, right? But we encourage caution and patience.

If it squishes, wait. Working with wet soil and turf damages it.

If it squishes, wait. Working with wet soil and turf damages it.

Here are tips to help gardeners navigate Chicago’s spring:

  1. Wait until the soil dries out to get back in your garden. If the soil can form a sticky ball when you squeeze a handful, it is still too wet for planting. Soil will take longer to dry after periods of cool weather. Sandy soils can be worked much sooner after a rain event. Clay soil holds more moisture and requires a longer waiting time.
  2. Avoid excessive walking in garden beds and on lawns. It can compact and damage your soil.
  3. Soil is ready for planting when it crumbles in your hand. Working the soil when it is too wet can increase compaction and break down the structure of the soil, leaving you with hard crusts or clumps when it dries out.
  4. Don’t mow a lawn that is excessively wet. A lawn is too wet when you see standing water, or water comes up from the ground as you step on the lawn. In these conditions, the mower tires will leave muddy tracks that will damage your lawn.
  5. Now is the time to get in some really satisfying weeding!

    Now is the time to get in some really satisfying weeding!

    Do pull weeds once your soil has dried a bit. Weeds are more easily pulled when the ground is moist (but not wet). Work from the edges of the beds to pull weeds without compacting soil or damaging other plantings.
  6. Mulch beds once the soil has dried out. Be sure the beds are sufficiently dry.
  7. Drainage issues? If you can, collect water that has pooled. In order to correct a drainage problem, you will first have to move the excess surface water that is pooling in low areas. Then you can consider the different options to improve drainage, taking into account soil type and natural changes in grade.

tomatoes on the vineThe Garden recommends waiting to plant warm-season flowering annuals, vines, herbs, and vegetables until after the Chicago area’s average last frost date of May 15. Cautious gardeners often wait until Memorial Day before setting out cold-sensitive plants such as tomatoes, peppers, eggplants, and squash.


©2017 Chicago Botanic Garden and my.chicagobotanic.org

The late February weather in Chicago has been a glorious time to be outside and work in the garden. But the unseasonably warm weather has also raised questions about the long-term effect on plants and what garden tasks are appropriate.

It is best to hold off on doing any detailed clean up of garden beds as the mulch and leaves in the beds will provide some protection to any early growing perennials when the weather eventually turns cold again. Raking leaves off the lawn and cutting back perennials are all fine to do now providing your garden soil is not too wet.

Snowdrops are blooming at the Garden.

Early flowering bulbs like snowdrops that are in flower here at the Chicago Botanic Garden are very tolerant of the cold. Daffodil and tulip foliage is coming up; these might end up being damaged by a spell of cold weather, but this should not affect the spring flowers. You do not need to take any special maintenance steps to protect these plants.

If you have some perennials that are growing in a warm area of the garden with more pronounced growth, they might benefit from a light layer of mulch. For the most part, though, there is nothing special for most gardeners to do in their perennial beds.

This is great weather to prune but proceed with care. Spring flowering shrubs like viburnums, lilacs, and forsythia set their flower buds last year so pruning done at this time of year will remove flower buds and reduce the number of spring flowers. You can still prune—just be aware of the flower buds as you are pruning. Forsythia flowers along the stems while viburnums will have a flower bud at the ends of the stem.

The dormant season, and in particular late winter, is the best time of year to complete rejuvenation pruning, which is the aggressive pruning of overgrown shrubs to bring them back into scale with the garden. Shrubs like hydrangea (except oak leaf hydrangea), potentilla, and spirea that flower on new wood respond well to pruning now too. For instance, I cut my Annabelle hydrangea back to the ground each spring.

Any plants installed last summer or fall should have been mulched when they were planted. If they were not, then mulch them now to help mitigate the temperature swings in the soil and prevent frost heaving of any plants in spring. The freezing and thawing of the soil can push recently installed small plants such as 1-gallon perennials or ground covers that were grown in containers out of the soil as the weather transitions to spring.

If we receive a good covering of snow, the snow itself will not harm plants unless it builds up on them and breaks branches. It is a good idea to brush plants off during a storm if you observe them getting weighted down. Later snowstorms are more likely to come in wet and heavy. Leave the plants alone if the snow has frozen on them to avoid breaking branches during the removal process.

Enjoy the warm weather and the early blooms, both at the Chicago Botanic Garden and in your own backyard.

While El Niño might be giving us a warmer winter, it’s never a bad idea to prepare against winter burn, or scorch. Three simple steps will make a big difference in preventing winter burn.

PHOTO: a burlap fence protects the Esplanade hedge from wind and deicing grit.

A burlap screen on the Esplanade path protects young boxwoods in this highly-trafficked area.

PHOTO: Viburnum winter damage.

Fencing may keep nibbling down in winter. This viburnum will need pruning.

Prepare properly

The right plant for your design goals should help reduce maintenance.

  • Choose the right plant for your garden’s growing conditions and design goals. A plant that is well-adapted to your site will perform better and have fewer problems. Proper siting makes a big difference for some plants. Plant salt tolerant plants along busy roads; broad-leaved evergreens perform best when sited so that they are protected from the winter sun and wind. The later in the season an evergreen is planted, the more at risk it is for winter burn.
  • Tree wrap may help prevent frost cracking in young, smooth-barked trees in some situations. Garden staff use tree wrap on a limited basis to protect certain plants from animal damage. Cut back herbaceous plants that are growing up around the base of trees and shrubs if you have had problems with vole damage in the past. The herbaceous plants provide cover for them in the winter while they are eating your plants. Fencing is more effective in keeping deer and rabbits away from plants.
  • Using burlap screens in winter can also help shade plants that need extra protection from the effects of wind, sun, and salt spray.


Plant well
 

  • Amend your soil with compost when possible, and install your new plants properly to get them off to a good start. Many trees and shrubs are planted too deep.
  • Be sure to break up the circling roots of plants that have been grown in containers before planting. The alternate freezing and thawing temperatures in spring can push out newly installed plants that are smaller in size or were grown in containers if not mulched well. Install one to two inches of mulch around the new plantings, taking care not to bury the crowns of perennials, or mounding the soil around the base of trees and shrubs. This will help prevent frost heaving in spring, and helps mitigate big temperature swings in the soil.


Provide good follow-up care

PHOTO: Andorra juniper with winter damage.

The brown-gray tips of Andorra juniper show where evaporation has damaged the foliage.

Commonsense care will go a long way to keeping plants healthy.

  • Provide supplemental water to newly installed evergreens in late fall when conditions are warm and dry so they do not go into winter under stress from being dry. Pay extra attention to plantings under 3 years of age.
  • Do not pile snow that has salt in it on plants. If you are using a combination of shoveling and ice melt on your driveway when snow is fast and heavy, make sure to shovel away from plants. Products that are safer to use are those containing calcium chloride, or calcium magnesium acetate. (Different products work differently at different temperatures.) Make sure to use the right amount as specified on the packaging! Mix ice melt with sand to reduce amount used, or use just sand near sensitive plantings.

©2015 Chicago Botanic Garden and my.chicagobotanic.org

Overcoming Winter Scorch

Tim Johnson —  April 29, 2014 — 9 Comments

Gardeners are facing bigger challenges than usual this spring due to a “perfect storm” of weather conditions that scorched evergreens, protected plant predators, elicited heavy use of road salts, and encouraged snow molds. The scorch or burn that has left patches of brown on arborvitae (Thuja), yews (Taxus), boxwoods (Buxus), and other evergreens is the worst and most widespread I’ve seen in my 29 years at the Chicago Botanic Garden. Branch damage from voles and rabbits is also particularly bad this year, and heavy and prolonged snow cover also promoted snow molds, creating bleached-out patches of lawn. Road salts put additional environmental stress on our landscaping.

PHOTO: A boxwood hedge with the outer foliage killed by winter damage.

Although slow-growing, this boxwood (Buxus microphylla) should make a full recovery.

The bad news is that more plant damage is likely to appear once the weather is consistently warm, though many plants will recover from the long, hard winter. While plants may have to be severely pruned or removed altogether, the polar vortex has given us a few important reminders about growing in the Chicago area and could ultimately make us all better gardeners.

PHOTO: A completely brown, winter burnt white cedar.

Winter was particularly hard on this Heatherbun white cedar (Chamaecyparis thyoides ‘Heatherbun’).

During the cold winter months, evergreens continue to lose water vapor through their leaves or needles. The leaves must replace the water by pulling it up from the roots. But when the ground is frozen, the plants’ roots cannot absorb water to resupply the leaves.

If the weather turns warm and sunny while the ground is frozen, evaporation from the leaves increases and the water cannot be replaced. The resulting symptoms, discolored or “burned” foliage, tend to show up quickly in spring, when days are sunny and warm.

Bright winter sun and strong winds can accelerate evaporation, and it’s typical to see the worst burning on the west- and south-facing sides of a bush or tree. Signs of winter burn include needles or leaves that have turned golden or brown. Sometimes a plant has an overall yellowish or off-green color. Leaves may appear bleached. Salt sprayed up by passing traffic can exacerbate the problem and accentuate damage on the road-facing side of the plant.

Many evergreens—particularly fast-growing varieties such as yews—will be fine after a light pruning. Deeply scorched plants will require heavy pruning, leaving unsightly “holes.” Slower growing evergreens may take years to recover from a severe winter burn, and gardeners must decide on a case-by-case basis whether it’s best to remove the specimen.

Unfortunately, some evergreens will be a total loss. This is especially true for plants grown at the edge of the hardiness zone. To determine whether a bush is going to make it, look for new buds or lightly scratch a branch to look for signs of green wood. Patience is often a virtue in gardening, so if you have any doubt about a plant’s viability, give it some time. 

PHOTO: A browned Bosnian pine, with fresh green growth at the tips of its branches.

This Emerald Arrow Bosnian pine (Pinus leucodermis ‘Emerald Arrow’) also shows hard winter damage.

The deep drifts of snow and prolonged snow cover were a boon to such plant predators as voles and rabbits. The blanket of snow shielded voles, mouse-sized creatures that travel under the snow, from hawks and other predators, leaving the creatures free to gnaw on branches and trunks. The drifts also provided a stepladder for rabbits, which feed on top of the snow, allowing them to reach higher into bushes. Signs of rabbit damage include a 45-degree cut in branches. Severe rabbit damage often looks like a bad pruning job, but gardeners can improve the situation by evening out the bush. Branches that have been girdled—or chewed all the way around—are likely to die and should be pruned back.

The sparkling white drifts also promoted snow molds, which can leave large patches of dead-looking lawn. Typically, lawns will bounce back after raking and light fertilizer. Lawns damaged by salt spray might not recover as quickly, and strips growing along roads might need to be replaced altogether.

PHOTO: Grass showing winter damage.

Grass showing winter damage will recover fairly quickly with attentive watering and care.

It’s never good to lose a plant or shrub to the elements, but the polar vortex did provide the type of reality check that can lead to best gardening practices. In a relatively mild winter, Chicago-area gardeners may have success with plants growing at the edge of their hardiness, but these plants can be killed or severely damaged in typical USDA Zone 5 conditions. Perhaps you’ll think twice in the future before putting something less-than-hardy in the garden. Good mulching and watering habits, and planting in the spring to give plants an entire growing season to become established, will increase the vigor of your plants and may help minimize winter burn.

Another virtue of gardening is that it forces you to look forward. So keep last winter’s lessons in mind as you clean, prune, maintain, and perhaps replant this spring.

For more information about gardening post-polar vortex, go to our free public Plant Information Service: chicagobotanic.org/plantinfoservice

©2014 Chicago Botanic Garden and my.chicagobotanic.org

Forsythia

Forsythia

If you are longing for spring blooms as much as we are, you might like to try forcing branches to bloom indoors! Spring-flowering trees and shrubs form their flower buds in late summer or fall before the plants go dormant for the winter. The buds can be forced into bloom indoors in late winter or early spring.

In order to flower, the buds need to undergo a period of cold. I’m sure you’ve noticed in the Chicago area, we’ve had plenty of cold temperatures this year! Now is a great time to cut branches from spring flowering shrubs for forcing indoors.

Once the branches are indoors in water it may take one to four weeks for the blossoms to open, although two weeks is typical. The closer to their natural bloom time you cut the branches, the sooner they will open.

Prune branches for forcing carefully, using proper pruning techniques, and cutting off only those branches that are not essential to the plant’s basic shape. On a day above freezing, cut branches at least 1 foot long that have plenty of flower buds. Flower buds are usually larger and more plump than leaf buds.
 
If you are pruning branches just for forcing, try to choose branches from more dense areas of the plant and cut them evenly around the plant, as you will be removing some of its natural spring display. Be careful not to disfigure the tree or shrub. Cut a few more branches than you expect to use, because some may not absorb water properly.

Redbud

Redbud

Place cut branches in a container of warm water. Then, while holding each stem underwater, make a fresh cut 1 inch from the base. Cutting stems underwater will help prevent air from entering the stem through the cut end and blocking water uptake.

Remove any buds and twigs that will be underwater in the vase. You may want to add a floral preservative to the container water to help control bacteria.

To start, keep the branches in a cool room out of direct sunlight and change the water every other day. When color appears on the buds or the foliage begins to unfurl, arrange the branches in a vase and display them in a cool room out of direct sunlight.

Some good choices for forcing include serviceberry (Amelanchier), magnolia (Magnolia), flowering quince (Chaenomeles), forsythia (Forsythia), crabapple or apple (Malus), flowering pear (Pyrus), flowering cherry (Prunus), viburnum (Viburnum), cornelian cherry dogwood (Cornus mas), and redbud (Cercis).

Learn more about how to force branches to bloom indoors in this video we taped in 2010 with Heather Sherwood, senior horticulturist in the English Walled Garden.

  

©2013 Chicago Botanic Garden and my.chicagobotanic.org