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Overwintering Marginal Plants

I keep seeing photos of interesting plants I’d like to grow, but they’re labeled zone 6 and I’m in zone 5. What can I do to successfully overwinter these marginal plants? I’d like to try them, but I don’t want to waste my money.

“Pushing a plant past the limits of its hardiness is not for the average gardener,” says Marie Dvorak of The Planter’s Palette in Winfield, “but plants can sometimes be successfully overwintered by siting them in a special microclimate such as a sheltered southern exposure.” Another tip comes from horticulturist Ann Hancock at Michigan State University, where they are trialing perennials that the English firm Blooms of Bressingham is introducing in the U.S. Hancock explains that the best way to keep perennials that are tender in Zone 5 or that are rated for Zone 6 is to grow them in raised beds with good drainage because poorly drained wet soils will cause the roots to rot. In addition, it is important to check perennial beds for plants that have heaved out of the soil through repeated freezing and thawing. Replace them in the soil and protect with mulch.

One example of a marginally hardy plant that will be getting attention this year is ‘Flamenco’, a new cultivar of Tritoma (Kniphofia, red-hot poker) that has just been named an All-America Selections Winner for 1999. Tritomas should have their foliage tied upright so water does not remain in the crown, said Hancock.


Cycas

I have a cycas palm and am not sure how much direct sunlight or water it needs. It has light brown marks developing on the leaves. What is causing this, and how do I care for my plant?

Cycas palms or sago palms (Cycas revoluta) are tough house or patio plants. They are neither palms nor ferns but primitive cone-bearing relatives of conifers. A rosette of green feather-like leaves, 2 to 3 feet in height, grows from a central point at the top of a single trunk.

Cycas need bright light and should be kept relatively moist with weekly watering. However, prolonged rainy spells can cause fungal leaf spot disease.

“The shiny brown spots are probably caused by scale,” says Jeff Frohn, sales associate at Geimer Greenhouses, Long Grove. “It can be treated with fish oil, vegetable oil or an all-in-one insecticide spray,” adds Mike Geimer, owner, Geimer Greenhouses.


Tree Position

What is the correct distance from my house to plant a tree? What is the correct distance from the lot line to plant a tree?

It depends on the size of the tree you are planting. A small tree such as a serviceberry (Amelanchier) or a dwarf flowering crab could be planted as close as four to five feet from the house. For a birch tree, a distance of six to eight feet would be the minimum.

Distance from the lot line does not matter as long as it doesn’t interfere with power or sewer lines. You should check with your village before planting. Closeness to the neighbor’s lot line is not an issue, because neighbors have the right to trim back any overhanging branches, according to Matt Zerby, partner in Wasco Nursery, St. Charles.


Perennial Pinchback

Is there an overall rule about when to pinch back my leggy plants?

“The reason plants are pinched back is to obtain compact and bushier growth. This is generally done three times during a growing season, or you can apply the 6 nodes rule,” says Jennifer Brennan, horticulturist, Chalet Nursery, Wilmette.

After 6 weeks of growth, trim back half of the growth, or wait until you see 6 nodes on the plant stem to trim back to get more branching. For plants that respond, such as chrysanthemums, use the 6 node criterion.


Birch Trees

I’d like to plant a white bark birch in front of my home in my sunny front yard. What can you tell me about Betula utilis var. Jacquemontii?

The birch, Betula utilis var. Jacquemontii is a tall, narrow tree (to 100 feet) with very white bark that’s native to India. It is subject to borers. The popular weeping white bark birch, B. pendula is also subject to borers in our climate and is not a suitable choice.

“There are better birch choices, so choose what grows well in our area,” advises Ken Morris, vice president of Spring Bluff Nursery in Sugar Grove. Two trees resistant to borers are the paper or canoe birch and the river birch.

Canoe or paper birch (B. papyrifera) has a stout trunk with creamy white bark that peels off in papery layers. It is native to North America. It is the first paper birch bred to resist the bronze birch borer, but it still needs to be monitored and sprayed yearly for the borers. A good cultivar is ‘Renaissance Reflection.’

River birch (B. nigra), native to the eastern United States, is fast growing when young. It can reach more than 50 feet in height. Its bark is a smooth, shiny apricot and, when mature, flakes and curls in cinnamon strips. It tolerates slow drainage and is also resistant to borers. “It’s pretty tough, good and sturdy,” says Morris.

The cultivar ‘Heritage’ was introduced to much acclaim around 15 years ago.

Birch trees need moisture. Do not allow your tree to dry out in your sunny site.


White Pine Trees

I have lost four 12-15 foot tall white pine trees over the last year. All had the same symptoms, browning needles at the bottom that continued up to the top. Can you tell me what pest is killing the white pines? I am also losing an Austrian pine now. It is experiencing the same symptoms.

White pines in this area are very rarely troubled by disease. They are, unfortunately, highly susceptible to high pH problems, or soil alkalinity, and are utterly intolerant of salt, according to Rich Eyre of Foxwillow Pines, Woodstock. The browning needles could also indicate the plant is getting too much water or has poor drainage.If environmental problems are not the issue for your white pines, consult an expert. Betty Lockwood, Plant Information Specialist at the Chicago Botanic Garden, suggested you bring them a sample branch to check on disease and bring in an arborist for an on site visit to check your growing conditions. Or take a 12-inch sample of an affected tree to your local extension office.Austrian pine is very tolerant of environmental conditions but is prone to certain diseases—diplodia tip blight and dothistroma needle blight, both caused by a fungus. Only an arborist or a laboratory can provide an accurate diagnosis. If you bring in a 12-inch sample for diagnosis, be sure to sterilize your pruning shears with denatured alcohol after cutting the diseased wood.


White Pine Burn

I have two 20-year-old pine trees whose needles are turning brown on the west side of the plants. On the east side I have a compost pile.

I live in the St. Charles region and my soil is mostly clay. What is causing the browning? Should I get rid of the compost? How do I correct the damage?

Climate conditions could be the cause of the brown needles. There was strong west wind this past winter season, which caused winter burn. With last fall’s rain and winter snow cover, the soil never dried out. According to Todd Mohr, sales associate, Rich’s Foxwillow Pines Nursery, Woodstock, pines normally begin

to go dormant in late August. “We had a lot of burn on our evergreens which showed up over summer,” says Mohr.

Cut a sample of the branch and make sure the plant is alive. You can photograph your tree or take the sample to an arboretum or garden center for evaluation. The compost should not affect the trees unless you have a large pile that is prohibiting air circulation. Spread the compost loosely over the area.

White pine is a native Illinois tree. It may come back on its own. If not, have a tree professional diagnose it.


What plants do you predict will be best sellers this year? Why?

What plants do you predict will be best sellers this year? Why?

Bryon Angerman, nursery manager, Alsip Home & Garden, St. John, Ind. and Frankfort, Ill.

I believe these two compact hydrangeas will be hot plants this year. First is Invincibelle Wee White® hydrangea, a compact and reblooming white variety of ‘Annabelle’ hydrangea. Its dwarf habit of 18-24 inches and versatile adaptability to full-sun to part-shade planting locations will yield three to four months of continuous flowers on sturdy stems. It’s sure to become a staple in every landscape. Also look for Mini Mauvette hydrangea for similar habits with pinkish purple flowers.

Molly Hornbaker Blogg, nursery manager, Hornbaker Gardens, Princeton.

Hydrangea Little Quick Fire will be a best seller this year. It blooms early with pure white flowers turning to pink, then rose. Its more
compact size, at 4-5 feet and fits into most urban gardens better than most other panicle hydrangeas. Hosta ‘Autumn Frost’ is an attention grabbing plant with powder blue leaves and showy yellow margins. Last year’s Perennial of the Year, Asclepias tuberosa, should continue to be a big seller because of its gorgeous orange flowers and because it is a host for monarch caterpillars.

Jennifer Brennan,horticulture information specialist, manager of education, Chalet, Wilmette.

Being at a retail garden center and nursery, I get to hear customers’ requests and questions about plants for their gardens. Being on the board of the Perennial Plant Association for 6 years, I get to hear hybridizers and growers claims about the “BEST” plants. It is wonderful when the claims of the hybridizers and growers match the requests of the gardeners and designers. The other fact that is worth stating is that the plants are trialed much better than in the past, so there is proof from many areas of the country that the recommended plants will perform and survive.

The first plant that I expect to be a good seller is one that has been selected by the members of the Perennial Plant Association as the Perennial Plant of the Year for 2018. It is Allium ‘Millenium’. Allium ‘Millenium’ is one of the very best ornamental onions. Unlike spring-blooming Allium bulbs, this hybrid Allium blooms in mid to late summer with large large 2 inch rose-purple, globe-shaped flowers over shiny deep green strappy, grassy foliage. Mature plants have dozens of globes covering this perennial plant. Allium ‘Millenium’ attracts butterflies and bees love it as well, but deer and rabbits stay away. This Allium is good for winter hardiness Zones 5-9; prefers full sun to part shade and is 10-12 inches tall.

The
second plant is a flowering perennial Echinacea. It is Echinacea KISMET™ Raspberry and it is different due to sheer flower number and a fabulous habit. It blooms first year, early in the season, with large flowers and continues until a hard frost. It is a great plant! I saw it in trials in the Chicago area and in Colorado. It attracts butterflies and hummingbirds. It is a wonderful cut flower with a great fragrance. It is deer resistant. It is hardy from Zone 4 to zone 10. It forms an upright mound that is 16 inches tall by 24 inches wide, up to 18 inches in flower. It is a beautiful hot pink color that blooms June, July, August, September and October. And, it likes average well drained soil in full sun.

The third plant is a hybrid of a native grass. Native plants are one of the strongest trends in gardening these days. The natural beauty of native Blue Grama Grass is raised to a higher level in Bouteloua gracilis ‘Blonde Ambition’. Its allure includes an abundance of horizontal seed heads, which resemble elegant, petite flags. They emerge chartreuse and transform to blonde. These exquisite blooms hover above thin, blue-green, two-foot stems. ‘Blonde Ambition’ was named a 2011 Plant Select® Winner for its resistance to pests, exceptional performance in low water conditions, retail appeal, and long-lasting attractiveness in gardens and containers. It pops right back up after snowfall. Bouteloua gracilis‘ Blonde Ambition’ was discovered and introduced by David Salman of High Country Gardens. It is easily grown in average, dry to medium, well-drained soils in full sun. It tolerates a wide range of soils, except poorly-drained, wet ones. It is hardy from Zone 3 to Zone 10. It is a tufted, warm season, Missouri native grass noted for its distinctive arrangement of mosquito larvae-like seed spikes which hang from only one side of its flowering stems. It is native to prairies, plains, open rocky woodlands and along railroad tracks. It has narrow, bluish-gray leaf blades (to 1/4 inch wide) that typically form a dense clump growing 12-15 inches tall. Foliage turns golden brown in autumn, sometimes also developing interesting hues of orange and red. Inflorescences of blond colored flowers appear on arching stems above the foliage in early to mid-summer, typically bringing the total height of the clump to 20 inches tall.

All three of these should be at the top of the selling lists for the 2018.


Powdery Mildew

My lilac had a grayish blight on the leaves this summer. What caused this and how can I prevent it?

Your lilac had powdery mildew, a common fungal disease. It occurs in late summer in humid weather, especially if your plant is located in a damp, shady area. While unsightly, it does not damage the plant since it only affects the outermost leaf cell layer. If it really bothers you, spray the leaves with a sulfur fungicide early in the season. If mildew appears late in the season, spray again.

Newer varieties of lilac are more disease resistant than the common lilac. Improving air circulation by pruning out any dead branches will also help to reduce mildew, advises Joan Barczak, owner of Blumen Gardens, Sycamore.


Houseplants

I have houseplants outside that I will need to bring indoors. What is the lowest temperature at which I can leave them outside?

The rule of thumb is when night temperatures are in the 50s, it is time to bring your houseplants indoors, according to horticulturists at Pesche’s garden center, Des Plaines.

To avoid the shock of suddenly bringing plants into a hot dry environment, place them in a shaded area before the heat comes on in the house. Bring in sensitive tropicals such as hibiscus and anthuriums as soon as summer cools down.

Christmas cactus and cymbidium orchids can tolerate chillier temperatures and stay outdoors longer, but move them indoors before the thermometer drops to freezing, says Greg Stack, University of Illinois Extension Educator, Horticulture. Indoors, a cool 50-degree area such as an unheated sun porch will give them the short day situation they need to set flower buds. Stack keeps his Christmas cactus in a cool unused room where the lights aren’t turned on. His plant sets buds and blooms reliably every year, he reports. Christmas cactus buds will dry up in an overheated, dry room.


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questions

I keep seeing photos of interesting plants I’d like to grow, but they’re labeled zone 6 and I’m in zone 5. What can I do to successfully overwinter these marginal plants? I’d like to try them, but I don’t want to waste my money.

What are some trends in gardening you see becoming more prevalent in the next few years?

Do the ants on my peony flowers help buds to open, or is this an old wives’ tale? What are the extremely tiny, microscopic yellow wormy looking bugs crawling on my pink peony flowers? My peonies are beautiful, but I don’t want all these bugs.

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