Extension Spring Garden Packet 3
Published: Feb. 23, 2009
NOTE TO EDITORS: This is the final installment of University of Illinois Extension's Spring Garden Packet. Thank you for your consideration. Bob Sampson
February 23, 2009
Source: Greg Stack (708) 720-7520 Contact: Bob Sampson Extension Communications Specialist Phone (217) 244-0225; rsampson@uiuc.edu
Clematis
What has often been termed the Queen of the Vines, clematis, can offer rich, striking beauty as does royalty, said a University of Illinois Extension horticulture specialist.
"At the same time, it can be very temperamental just as some royalty can be," said Greg Stack. "But once you have decided to include clematis in your garden, there are a few things that should be noted so your 'royal resident' will find your garden to its liking."
Clematis are members of the buttercup family and have well over 300 species and countless man-made hybrids in the group. Not all of these are suited to Midwestern gardens and so selection needs to be done carefully.
Clematis are mainly woody, climbing plants. They do not attach themselves to supports by twining stems, aerial roots or tendrils.
"However, they attach by twining their leaf petiole around support structures," he said. "Because of this, thought has to be given to providing the proper supports otherwise they will ramble along the ground until they do find suitable support.
"The best supports are those things that are less than three-quarters of an inch in diameter. Clematis petioles find this size to be the easiest to wrap around. Many gardeners find that using heavy fishing line is a good way to get clematis to climb up poles or arbor posts."
If a knot is tied in the line at 12 inch intervals, this will help keep the vine from sliding down the fishing line, he added.
In the wild, clematis is often found growing at the edge of woodlots where they climb through the tree limbs to reach full sun while their roots remain in the shade.
Success with clematis starts with proper soil preparation, planting, and after planting, pruning.
Clematis prefers a cool, moist, well-drained soil for best growth. They do not like poorly drained soils especially those that stay wet over the winter. While it is true that clematis prefers alkaline soils, they will grow successfully in soils that are neutral (pH 7.0) to slightly alkaline (pH 7.5). To determine if liming is necessary, a soil test should be taken to guide you on how much if any lime needs to be added. Annual liming is not suggested as over-liming can lead to other nutrient deficiencies.
"When preparing the planting site, be generous with the planting hole," he said. "Dig a hole at least twice as wide as the pot the plant is in and at least twice as deep. This allows for adequate organic matter to be incorporated into the site, a key to good root development.
"When planting, plant deep. Place the crown of the plant at least two to four inches below the surface of the soil. This will help with the production of stems from dormant buds below the soil and also helps the plant recover if stems are injured by animals or mechanical means."
Newly-planted clematis should be pruned back to about 12 inches in the spring following planting. This pruning will encourage new shoots to develop and will produce a fuller, bushier vine with many more stems and a not-so-bare bottom.
Clematis like to be fed but not overfed. Fertilizing in the spring with a general purpose fertilizer right after pruning should carry the plant through the season.
"Because clematis prefers cool soils, some type of mulch should be used over the root area," Stack said. "Planting a low perennial groundcover near the plant often works well or organic mulch can be used.
"Apply about four to six inches of mulch at the base of the plant, keeping the mulch about eight inches from the stems to avoid stem rots."
Now comes the mystery for many gardeners when growing clematis: when, how and where do I prune?
Stack answered that pruning clematis is not complicated and even if done incorrectly it is not fatal. The worst that can happen is you will either delay flowering or flowering does not occur for a year.
Clematis is divided into groups or categories for pruning purposes. They are designated as A, B, C or 1, 2, 3, or hard, half pruning or none, depending on what source you are reading. In any case, always look at the tag that accompanies your plant. It will often mention the pruning category your plant falls into. Take note and there will not be any doubts.
For group A, these plants flower on "old wood" or last season's stems. For these varieties only light pruning is done in the spring to remove dead stems. Another pruning opportunity occurs right after the plant has finished blooming. Prune in late spring or very early summer. The resulting new growth now becomes next season's flowering stems.
Group B clematis flower on both old and new wood. Because of this it can make pruning a bit more challenging. Prune lightly in spring, removing dead and weak stems. The largest flowers will be produced on the old wood while new growth will provide bloom for late season. If a group B clematis ever needs major pruning to rejuvenate it, a hard cutting back can be done right after spring flowering and still have plenty of time for the new shoots to provide a fall show of blooms.
Group C is the easiest. Here you grit your teeth, grab your pruners and cut the plant down to eight to 10 inches. By doing this you will ensure a lot of vigorous shoots from the base and a nice, full plant covered with flowers. Many group C clematis are often not pruned hard enough and the result is a rather "trashy" looking vine with lots of tangled stems.
"One problem that is frequently seen with clematis is clematis wilt," he said. "This problem has been attributed to a fungus and is most damaging early in the growing season when the plants start flowering. Leaf spots and partial stem rot occurs, resulting in wilted stems.
"This can happen slow or fast. Fungicides have been used as a preventative control but once the plant is affected the only suggested control is to prune out affected stems at least 2 inches below the point of infection. Most experts agree that clematis wilt is not fatal and most will re-sprout from buds located lower down on the stem."
To get you started with clematis or to add to your current collection, here are a few suggested varieties that exhibit good performance and interesting flowers:
Anne-Louise - Violet purple flowers with contrasting red-purple stripe. Blooms May-June and August—September Group B
Arctic Queen — Fully double white with a very strong habit. Blooms May — August Group B
Crystal Fountain — Lilac blue flowers with a fountainlike center. Compact plant good for small gardens and containers. Blooms June-September Group B
Franziska-Maria — Blue-purple fully double flowers. Good for containers. Blooms on old and new wood. Blooms June-September Group B
Rosemoor - Large rose-colored flowers. Blooms on old and new wood. Blooms May-September Group B
Rouge Cardinal — Large velvet crimson flowers. Blooms June-August Group C
Polish Spirit — Rich purple. Good cut flower. Blooms July-September Group C
Tangutica — Small yellow bell-shaped flowers. Vigorous grower, attractive seed heads. Blooms July-September Group C
Duchess of Albany — Pink bell-shaped flowers with red stripe. Vigorous grower. Blooms July-October Group C
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February 23, 2009
Source: Jeff Rugg (630) 553-5823 Contact: Bob Sampson Extension Communications Specialist Phone (217) 244-0225; rsampson@uiuc.edu
Tropical Plants
As spring weather slowly works its way up from the south, so does the heat and humidity, said a University of Illinois Extension horticulture educator.
"You know you are going to have a bad day when the thermometer and the humidity gauge both follow the clock," said Jeff Rugg. "At 7 a.m., they are both in the 70s and by 10 a.m. they have both reached 100.
"If you think you have it bad, think about your plants. They cool themselves with water evaporating off the leaves, but when the humidity is high, they can't stay cool."
Some plants grow in hot and humid jungles and aren't affected as much by the heat and humidity. Tropical locations often have high humidity because of frequent rainfall, sometimes even daily. The plants are cooled by the rainfall and have plenty of moisture available to the roots.
In the United States, hot weather is often rain free, but the humidity stays high because of weather systems that come off the oceans or the Gulf of Mexico. The Gulf humidity often moves north past the Gulf States and into the Plains States and the Midwest.
"If you have a hot and humid patio that has pots of tropical plants, you may need to add some irrigation to keep your plants healthy," he said.
"Call me crazy, but I like the heat and humidity. I also like a lot of the plants that thrive in these conditions. Here are a few of my favorites."
Annual vinca (Catharanthus roseus) is not the same plant as the vinca vine that many people use in hanging baskets or as a groundcover. It is an annual that thrives in the heat. It will bloom all summer with white, pink or rose-colored flowers. It grows a foot to eighteen inches tall. Although it is trouble free and needs occasional watering to keep it blooming, it does not do well if it gets too much water.
There are other annuals that will thrive in heat and humidity. Try Alternanthera with hot pink to purple foliage. Coleus has dozens of varieties that have gorgeous combinations of colors on the leaves. Annual salvia, euphorbia and helianthus are also good.
"I especially like summer bulbs," he said. "They almost always have pretty flowers and many have a pleasing fragrance. They are easy to take care of and have few pest problems. For hot and humid conditions, you can't beat agapanthus and crinums, which are both also deer resistant."
As many as 50, two-inch-long agapanthus flowers form a ball, are borne on one-to-four foot stalks, and come in a variety of blues and white. They form clumps of bulbs with two-foot-long green leaves that are a couple of inches wide. The name agapanthus comes from the Greek words for flower of love, but it is commonly known as the Lily of the Nile.
"Crinum X powelli is the botanical name of what may be my favorite bulb," Rugg said. "Southerners commonly call it a spider lily or rain lily. They look a lot like amaryllis. Digging up an old clump to divide them among friends may take all day.
"The bulbs are often the size of a football with leaves longer than six feet tall that tend to topple over about halfway up to form a fountain-shaped clump. Newer varieties are smaller and more refined."
The flowers are the size and shape of an Easter lily flower and come in white, pink, purple and striped varieties. They are sweetly fragrant and attract butterflies and hummingbirds. Each flower stalk can bear a dozen flowers, and each clump of bulbs can send up dozens of flower stalks, usually within a week or so after a drought-breaking rain.
The bulbs not only take the heat without blinking, they can take several freezes each winter. They can be left outside in zone six. In northern states they need to be brought in, just like a canna or a dahlia
Crinum americanum is a native North American bulb that grows in wet soil or up to several inches deep in the water from the Everglades, around the Gulf Coast and down into South America. It has white fragrant flowers and makes a wonderful addition to any water garden. In northern climates it makes a good house plant over the winter.
"You cannot beat the fragrance of the plumeria or fangipani," he said. "It is used to make the lei necklaces that are given to visitors to Hawaii. They are not the prettiest shrubs when not in bloom and especially when the deciduous species drop their leaves, but they are worthy of growing in every warm garden or in a pot, just to smell the flowers."
For a beautiful flowering shrub or small tree that thrives in heat and humidity, you can't beat hibiscus rosa-sinensis. The flowers come in every variety of red and pink from orange to scarlet, with some whites and yellows thrown in for good measure.
"The flowers are generally wide open and flat, but newer ones come in doubles and in spider forms," he said. "Probably the most important thing to know about growing hibiscus flowers is to keep the soil damp, but not too wet. If it dries out, the flower buds tend to fall off. Small amounts of daily watering will help a lot in keeping this plant in bloom."
When one thinks of tropical plants, a common characteristic of huge leaves is often brought to mind. Few plants have bigger leaves than colocasia, also known as elephant ear; this bulb has leaves that are used as umbrellas in the tropics.
It is often sold as an annual in northern states, but the bulb can be brought in and stored over the winter. It needs plenty of water and actually grows quite well in the shallows of a water garden.
Another big-leaved plant is the banana.
"If you want to eat bananas from your plant, you will need to have it in a frost-free area for 12 to 18 months," Rugg said.
If you are looking for hot-and-humid-tolerant tropical plants to grow, try the hot and humid, Louisiana-based Stokes Tropicals catalog.
"They have bamboo, ginger, plumeria, and many other beautiful tropical flowers," he said. "They also have bananas, including the Japanese fiber banana that is hardy to minus 3 degrees Fahrenheit when planted in the ground and to minus 24 degrees if given proper mulching.
"If I could find the right piece of land, I would order every plant in the catalog. Check them out at www.stokestropicals.com or 866-478-2502."
There are a lot of reliable catalogs offering tropical plants, but whenever possible Rugg prefers to have tested plants from reliable testing facilities. For plants that need to grow in hot and humid conditions, the test location needs to be hot and humid.
"Dr. Allan Armitage has just the spot at his University of Georgia trial garden," he said. "The annual and perennial flowering plants he recommends are not just heat and humidity tolerant, he also checks them to make sure they are virus free.
"This virus check is an amazing feature that I don't think any other testing program does. He searches for unique plants that are particularly pretty and perform well in the landscape or in containers. They are promoted under the Athens Select™ label which gives some money back to the university."
Having done the testing for more than 10 years, you might expect there would be a large number of available plants, but only about 30 plants have made the University of Georgia's list so far.
"What these plants lack in quantity, they make up in vivid colors," he said. "You will not be at a loss for color if you chose one of these plants. Eighteen of the plants have variegated leaves and several of them also have attractive flowers. These plants don't require heat and humidity, so anyone can grow them all summer long, unless they have full shade or are in a really cool location, such as in a higher altitude region."
One plant that many deep southerners wish they could grow is the red, cut-leaved varieties of Japanese maple. It is a small tree or large shrub with ferny-looking foliage that grows in the cooler northern zones of 5 through 8. In the warmer areas, they often lose their red color early in the season.
The closest look to the northern maple is provided by the two red cut-leaved hibiscus plants called Panama Bronze and Panama Red. They grow four feet tall and wide and grow in zones 8 —11. They do not bloom very often, but have large red flowers when they do.
A two-foot-tall house plant from years ago, the flowering maple is making a comeback. The Fairy Coral Red hybrid Abutilon has salmon pink flowers and grows well in patio containers or the landscape in zones 7 —11.
Lantanas have always been good plants for full sun hot spots, and Athens Select™ has two that can be used in flowerbeds, containers, hanging baskets or even as a groundcover. The first is Athens Rose that has flowers that start out magenta red and fade to yellow. New Gold has bright yellow flowers held above dark green leaves.
"The Ron Deal verbena is the real deal," said Rugg. "It has fragrant rose-purple flowers and can be used in hanging baskets, containers to spill over the edge, and as a groundcover."
To find more information on the whole plant list from Athens Select™ and where you can buy them locally, check out the web site at: www.athensselect.com.
"Just about everyone has the potential to grow tropical plants if you can do a couple of things to your landscape," he said. "First, to make it more livable for you and your family, you might want to try adding a misting system or an automated irrigation system for the plants. "Check with your local licensed irrigation installer to see about adding the mist. Water is an amazing substance. Liquid water sprayed on the concrete patio will take a lot of the heat out of the concrete just to change into a gaseous form at the same temperature and then it evaporates away taking the heat with it."
Spraying a mist into the air and letting it evaporate from liquid drops into water vapor will take the heat out of the air. A misting system that is on a timer can keep your patio cool enough for your plants and for you to use during the day and evening. Even just using it manually just before you use the patio will help a lot. The mister uses very little water and cooler plants will need less water for irrigation, so there is a water savings there.
Another thing you can do for the plants is to automate the watering system for them.
"Many people don't realize that individual flower pots and hanging baskets can be watered with small tubing on an automatic system" said Rugg. "In fact, many of these plants were watered that way in the greenhouses they were propagated in.
"There are do-it-yourself kits available that hook up to a timer and the garden hoses or they can be connected to the irrigation system. Using an automated system will cut back on the labor of watering, get water to the plants at the proper time, which keeps the plants healthy and blooming and uses less water."
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February 23, 2009
Source: Sharon Yiesla (847) 223-8627 Contact: Bob Sampson (217) 244-0225 Extension Communications Specialist e-mail: rsampson@uiuc.edu
Multi-Season Shrubs
Shrubs can be expensive so it pays to take the time and select the right one for your yard, said Sharon Yiesla, a University of Illinois Extension horticulture educator.
"The shrubs presented here were selected based on having multi-season interest, requiring lower maintenance and/or being able to endure tough conditions," she said.
There are a number of things to consider when selecting a shrub. First, select a shrub that is winter hardy in our area (zone 5). Also consider soil conditions such as pH and drainage. The shrubs presented here, for the most part, are shrubs that tolerate a variety of soil conditions, Yiesla explained.
To get the most out a shrub, look for one that has multi-season interest (flowers, fall color, even foliage that stays good looking all season). A shrub that looks good in more than one season can be a real attribute to the landscape.
It is always important to consider how tall and wide a shrub will get, so we know that we have room in our yard for that particular specimen. Size can also affect form. If we give a shrub enough room to grow, it will develop a characteristic form. If the shrub is crowded, it will be misshapen. A shrub with good form can be a good visual asset in the landscape.
Always consider maintenance needs. Some shrubs are high maintenance due to pests, messy fruit or weak wood. The shrubs presented here tend to be lower maintenance. Caryopteris x clandonensis (Bluebeard) grows 2-3 feet tall, with a similar width. It grows in full sun to partial shade and is drought tolerant. This plant is often sold as a perennial instead of a shrub, and it can be cut to the ground each year because it flowers only on new wood. Ornamental features include gray green foliage, clusters of small blue or blue-purple flowers from late summer into fall and clusters of light brown seed heads that last well into winter. This plant has no common serious problems.Cultivars include 'Dark Knight' which has deep purple-blue flowers and 'Azure' which has bright blue flowers.
Fothergilla gardenii (Dwarf Fothergilla), a U.S native, grows 2-4 feet tall with a similar spread. It grows in full sun to partial shade and prefers (but does not demand) a slightly acid soil. Good drainage is important.
Ornamental features include small, fragrant white flowers in 1-2 inch bottlebrush like clusters in spring; leathery, dark green leaves resemble those of witchhazel and excellent fall color (a mix of yellow, orange and scarlet). This plant has no common serious problems.
Kerria japonica (Japanese Kerria) grows 3-5 feet tall, with a similar to slightly larger spread and an arching mounded form. This versatile shrub can grow in part to full shade and needs moist, well-drained soil.
Ornamental features include yellow, five-petaled flowers in mid-spring; crisp, bright green leaves; an arching form; mild yellow fall color and bright green stems all winter. This plant has no common serious problems.
Cultivars include 'Golden Guinea' which has flowers larger than those of the species, and lasting for a longer period; 'Picta' ('Variegata') with leaves edged with white; best grown in some shade to avoid burning the leaves and 'Pleniflora' with double flowers.
Physocarpus opulifolius (Common Ninebark), native to the United States, grows 5-10 feet tall, with a similar to slightly larger spread, rounded form, and upright, slightly arching stems. This shrub grows in full sun to partial shade and is best in moist, well-drained soils It can tolerate alkaline soil and both wet and dry sites.
Ornamental features include clusters of small, white or pinkish flowers in late spring and early summer; medium green leaves, seldom marred by insects or diseases; mild yellow to reddish fall color; clusters of pinkish fruit capsules from late summer into fall; and peeling bark on older stems. This shrub also has no serious common problems.
Cultivars include 'Diablo' with red-purple to maroon leaves and 'Summer Wine' which has wine-colored foliage and is about half the size of the species.
Rhus aromatica (Fragrant Sumac), also native to the United States, grows 2-6 feet tall with a 6-10 foot spread. It grows in full sun to shade and prefers moist, well-drained soils. It will tolerate dry soil and grows more slowly in wet soils.
Ornamental features include very glossy leaves all season; bright red fruit on female plants in late summer and orange-red to red-purple fall color. Leaf spots, aphids and scale insects are occasional problems.
The most popular cultivar is 'Gro-Low,' which is only 2 feet tall with good fall color. Viburnum trilobum (American Cranberrybush Viburnum), native to the United States, grows 8-12 feet tall and wide. It grows in full sun to partial shade and is best in moist, well-drained soils. It tolerates wet soils and is pH adaptable.
Ornamental features include white, 'lacecap' type flowers (a ring of showy sterile flowers surrounding a cluster of tiny, fertile flowers) in spring; deep green foliage, with a maple-like shape; yellow-red or reddish purple fall color and bright red, cranberry-like fruit which will shrivel in late winter like red raisins. The fruit is edible and often used for jelly. There are no serious common problems.
-30- February 23, 2009
Source: Richard Hentschel (630) 685-2317 Contact: Bob Sampson Extension Communications Specialist Phone (217) 244-0225; rsampson@uiuc.edu
Apple Scab on Flowering Crabapples
Every year when the weather has been cool and wet in the spring, homeowners find their flowering crabapples with olive green spots on the leaves, said a University of Illinois Extension horticulture specialist.
"Worse than that, by mid-summer nearly all the leaves have fallen, leaving just a few at the ends of each branch for the remainder of the summer," said Richard Hentschel. "This leaves you with a tree that will be stressed and lacking in the production of nutrients since it is the leaves that are the "food factory" for the tree, besides the flowering crabapple not looking very good.
"This is the same foliar disease commercial and home orchardists face on a number of apple varieties. This is a fungal disease called Apple Scab."
Apple Scab overwinters on the decaying leaves laying underneath your crabapple and surrounding area. When the early spring wet weather arrives, the disease becomes active and releases spores into the air. These spores then infect the newly developing leaves on your tree. Apple scab can also attack the crabapple fruits themselves, but since we do not eat those fruits, it is the foliage loss that bothers us most.
"So what is a homeowner to do? Culturally, raking up the leaves and crabapples for disposal is a very good start — remove the source and you lessen next year's outbreak," he said. "Homeowners will not be entirely successful just raking the old leaves and crabapples up since the spore is airborne and can float into your yard from anywhere in the neighborhood, but you sure will have a lot less disease."
Pruning your crabapple for more sunlight penetration and air movement will allow the foliage to dry sooner, limiting the time when fungal spore can penetrate the leaf and infection takes place.
If you have the opportunity to plant a new flowering crabapple, there are many new disease-resistant cultivars on the market, be sure to ask about Apple Scab resistance before you make your selection.
"Do your homework ahead of time and list the crabs you are interested in. Today flowering crabapples come in a variety of plant shapes, mature plant sizes, levels of disease resistance and flower color," he said.
Homeowners interested in treating susceptible crabapples can consider topical treatments to the foliage along with the cultural practice of sanitation each fall. Treatments will need to be applied several times during the early spring when the spores are in the air and while the weather remains cool and wet.
"These treatments must start as the leaves are expanding out of the buds and continue until the leaves are nearly full grown or about ¾ of the flower petals have fallen," he said. "Once warmer, drier weather arrives, most of the spores cannot survive the time it takes to float to the leaf and infect it. If you are growing fruit trees in your yard too, those will need to be sprayed for Apple Scab throughout the season to protect developing fruit."
Look for Apple Scab on the label of the fungicide sprays you are interested in using.
"Most multipurpose fruit tree sprays contain the right material," Hentschel said. "Remember that as the tree develops more foliage, more spray per tree will be needed and complete coverage of each leaf is necessary."
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