动态第842页 - 绿手指 - 养花技巧、花生病了怎么办、花园打理和设计

2017年08月30日

Dogwoods are among the most beautiful trees found in American landscapes, but not all types are suitable for the garden. Find out about the different kinds of dogwood trees in this article.[图片]Dog Tree Types Of the 17 species of dogwood native to North America, the four most common garden types are native flowering dogwoods, Pacific dogwood, Cornelian cherry dogwood and kousa dogwoods. The latter two are introduced species that have earned a place in American gardens because they are more disease resistant than native species. Other native species are best left in the wild because of their coarse texture or unruly habit. Let’s look at the four different types of dogwood trees best suited to cultivated landscapes.[图片]Flowering Dogwood Of all the varieties of dogwood, gardeners are most familiar with the flowering dogwood (Cornus florida). This beautiful tree is interesting all year, with pink or white flowers in late winter or early spring, followed by attractive green foliage. In late summer, the leaves turn dark red, and bright red berries appear in place of the flowers. The berries are an important food for several types of wildlife, including many species of songbirds. In the winter, the tree has an attractive silhouette with small buds at the tips of the branches. Flowering dogwoods grow to between 12 and 20 feet tall with a trunk diameter of 6 to 12 inches. They thrive in sun or shade. Those in full sun are shorter with better leaf color, especially in the fall. In the shade, they may have poor fall color, but they have a more graceful, open canopy shape.[图片]Native to the Eastern U.S., this handsome tree thrives in U.S. Department of Agriculture plant hardiness zones 5 through 9. Flowering dogwood is susceptible to anthracnose, a devastating and incurable disease that can kill the tree. In areas where anthracnose is a problem, plant kousa or Cornelian cherry dogwood instead. Kousa Dogwood Native to China, Japan and Korea, the kousa dogwood (Cornus kousa) is very similar to the flowering dogwood. The first difference you will notice is that the leaves appear before the flowers, and the tree flowers a couple of weeks later than the flowering dogwood. The fall fruit looks like raspberries, and it’s edible if you can tolerate the mealy texture. If you’re going to plant near a patio, flowering dogwood may be a better choice because the kousa’s berries create a litter problem. It tolerates the cooler temperatures of zones 4 through 8. There are several noteworthy hybrids of C. florida and C. kousa.[图片]Pacific Dogwood Pacific dogwood (Cornus nuttallii) grows on the West Coast in a band between San Francisco and British Columbia. Unfortunately, it doesn’t thrive in the east. It’s a taller and more upright tree than the flowering dogwood. Pacific dogwood thrives in USDA zones 6b through 9a.[图片]Cornelian Cherry Dogwood Cornelian cherry dogwood (Cornus mas) is a European species that thrives in zones 5 through 8, although it looks ragged by the end of the season in areas with hot summers. You can grow it as a small tree or a tall, multi-stemmed shrub. It reaches heights of 15 to 20 feet. It blooms in late winter or very early spring, with the yellow blossoms making their appearance before early spring-bloomers such as forsythia. You can use the cherry-like fruit in preserves.

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2017年08月30日

Propagating dogwood cuttings is easy and inexpensive. You can easily make enough trees for your own landscape, and a few more to share with friends. For the home gardener, the easiest and fastest method of dogwood tree propagation is taking softwood cuttings. Find out how to grow dogwood cuttings in this article.[图片]Propagating Dogwood Cuttings Knowing when to take cuttings of dogwood stems can mean the difference between successful propagation and failure. The best time to cut is in the spring, as soon as the tree completes its bloom cycle. You know the stem is ready to cut if it snaps when you bend it in half. Cuttings aren’t always successful, so take more than you need. The cuttings should be three to five inches long. Make the cut about an inch below a set of leaves. As you take cuttings, lay them in a plastic basin lined with damp paper towels and cover them with another damp towel.[图片]Here are the steps in starting dogwoods from cuttings: Remove the bottom set of leaves from the stem. This creates wounds to let the rooting hormone in and encourage root growth. Cut the remaining leaves in half if they are long enough to touch the soil when you bury the end of the stem 1.5 inches deep. Keeping the leaves off the soil prevents rot, and shorter leaf surfaces lose less water. Fill a three-inch pot with rooting medium. You can buy commercial medium or use a mixture of sand and perlite. Don’t use regular potting soil, which holds too much moisture and causes the stem to rot before it roots. Moisten the rooting medium with water. Role or dip the bottom 1.5 inches of the stem in rooting hormone and tap it to remove the excess.[图片]Stick the lower 1.5 inches of the stem in the rooting medium and then firm the medium so that the stems stand straight. Mist the cutting with water. Place the potted cutting inside a large plastic bag and seal it to create a mini greenhouse. Make sure the leaves don’t touch the sides of the bag. If necessary, you can hold the bag away from the plant by placing clean wooden sticks around the edge of the pot. Check the dogwood cutting for roots once a week. You can look at the bottom of the pot to see if roots are coming through or give the stem a gentle tug. Once roots form, the stem will resist a tug. You should find that the cutting has roots within six weeks.[图片]Remove the plastic bag when you’re sure you have roots, and place the new plant in a sunny window. Keep the soil moist at all times. Use half-strength liquid fertilizer every two weeks until the plant is growing well. When the dogwood cutting outgrows its little pot, repot it into a larger pot filled with regular potting soil.

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2017年08月30日

Flowering dogwoods are native to most areas of the eastern United States. They are useful as understory trees for partially shaded locations or even a fully sunny site, but often planted in improper locations and require transplanting. Can dogwood trees be transplanted? They certainly can, but follow a few tips on when to move a dogwood and how to do it correctly beforehand.[图片]Can Dogwood Trees be Transplanted? Dogwoods are lovely plants with four seasons of interest. Their characteristic flowers are actually bracts, or modified leaves, which surround the actual tiny flower. In fall the leaves turn red and orange and bright red fruits form, which birds adore. Their year-round beauty is a boon to any garden and should be preserved. If a dogwood needs to be moved, choose a site that is suitable so it doesn’t need to be moved again. The trees do well in dappled light in well-drained soil that is moderately acidic. Consider the height of the tree and avoid power lines and sidewalks. It is common to misgauge the height or width of a foundation plant, requiring the need to move it. Dogwoods also often fail to flower because over story trees have gotten so dense there isn’t enough light to fuel blooms. Whatever the cause, you need to know a few tricks for transplanting dogwoods.[图片]When to Move a Dogwood Dogwood tree transplanting should be done when they are dormant. This would be when the leaves have dropped and before bud break. Provided your soil is workable, this could be in the middle of winter, but northern gardeners will have to wait until early spring. Transplanting dogwoods earlier can damage the plant’s health because the sap is actively running and any injury to the roots can invite rot and disease, or even girdle the plant.[图片]How to Transplant a Dogwood Tree A good idea to maximize the health of the tree and prevent transplant shock is to root prune. This is done the season before you will move the tree. Prune the roots in October for an early spring transplant. Cut a trench around the root zone that you desire, severing any roots outside the circle. The size of the root ball varies dependent on the size of the tree. Clemson Cooperative Extension has a root ball sizing table available online. After the winter season is nearly over, it is time to transplant the tree. Tie up any errant growth to protect branches. It is a good idea to dig the hole first, but if you don’t, wrap the root ball in moist burlap. Use a sharp spade to cut around the area where you root pruned and then under-cut the tree at a 45-degree angle.[图片]Place the soil and root ball on the burlap and tie it around the base of the trunk. Dig the hole twice as large and twice as deep as the root ball with a hill of dirt at the center base. Unwrap the tree and spread the roots out. Back fill, taking care to use the substrate soil first and then the topsoil. Pack the soil around the roots. A good method is to water in the soil so it sinks around the roots. Fill up to the original soil line and water well to pack the soil.[图片]Back fill, taking care to use the substrate soil first and then the topsoil. Pack the soil around the roots. A good method is to water in the soil so it sinks around the roots. Fill up to the original soil line and water well to pack the soil. Keep the tree well watered until it establishes. Don’t panic if it loses a few leaves, as it will perk up in no time.

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2017年08月30日

The giant dogwood has such an appealing appearance that it’s also known as wedding cake tree. This is due to its tiered branch structure and elegantly variegated white and green leaves. Wedding cake tree care for young plants should be consistent until establishment but mature variegated giant dogwood trees are quite hardy and tolerant provided they are kept moist. Read on to learn more about this interesting flowering dogwood variety.[图片]Giant Dogwood Information The wedding cake dogwood has the grown up moniker Cornus controversa ‘Variegata.’ This lovely tree grows up to 50 feet tall but more commonly 25 to 30 in height. It is a native of Asia, which can be planted in United States Department of Agriculture zones 5 through 8. These trees are easy to grow and susceptible to only a few pests and diseases.[图片]The wedding cake dogwood is a fast growing tree that does well in either partial shade or full sun. The limbs are horizontal, giving the appearance of layering, but as the plant matures they tend to droop a bit. In spring, it produces a brilliant display of creamy white flowers. An interesting nugget of giant dogwood information reveals these flowers to be leaves. The flowers are actually bracts, or modified leaves, that form around the very tiny and mundane real flower. The flowers develop into bluish-black berries that are favorites of birds, squirrels and other animals. In fall, the leaves turn a rich red and in spring the bright green tops of new leaves compliments the variegated silvery white tinged under leaves.[图片]Growing a Giant Dogwood Tree These trees are not found in many nurseries, but if you are lucky enough to find one, take care to situate it in a good location and provide basic wedding cake tree care as it establishes. The best place for variegated giant dogwood trees is in slightly acidic soil where there is dappled lighting. It will also perform well in full sun situations. You can plant it in either clay or loam but the soil should be slightly moist but not boggy. Take care to provide enough space above and on the sides for the adult height and spread of this majestic tree.[图片]Care of the Wedding Cake Dogwood After planting, it is a good idea to stake the young tree for straight strong growth. Provide water weekly for the first few months, and thereafter supplement moisture in very dry periods and in summer with a deep drench every couple of weeks. This tree is resistant to many pests but does occasionally has a problem with dogwood borers and scale. It is resistant to Verticillium but may become prey to canker diseases and root rot. Overall it is a very easy tree to care for and worth having for its many seasons of interest.

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2017年08月30日

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2017年08月30日

Dogwoods are native ornamental trees. Most flower and fruit, and have dazzling fall displays as the leaves change color. Peeling bark on dogwoods may be the result of serious disease or it could be a natural condition in some species. Knowing the species of your tree is crucial to deciding if a dogwood with peeling bark is in danger or if it is a normal occurrence. Dogwood is both a native and introduced species across North America, especially the cooler climates. The plants may be trees or shrubs in form, but all of them offer extraordinary color and many of them flower.[图片]Many of the varieties are deciduous and provide a rich fall color display followed by bright green, yellow, coral and orange revealed stems. They are quite winter hardy but are sensitive to mechanical injury and a variety of pests and diseases. For this reason, the tree bark flaking on dogwood trees may be the result of a canker, borer, string trimmer or fungal disease, to name but a few.[图片]When a Dogwood with Peeling Bark is Normal The Kousa dogwood is an ornamental tree that is more cold tolerant than flowering dogwood. It has bark which peels off in irregular patches, revealing a mosaic of mottled colors underneath. The dogwood bark peeling off is part of this tree’s appeal, along with its winter interest and fall display of purple leaves. Other times that peeling bark on dogwoods may be normal is when it occurs due to wild herbivores rubbing their antlers or standing on the trunk. Small rodents may also chew on trunks and cause sloughing bark. None of these conditions are good for the tree but would be categorized as wildlife problems and completely normal in certain regions. Sunscald on young trees may also result in peeling bark. It is a good idea to site them where winter sun won’t be aggressive or paint the trunk with latex paint thinned with water. Drought conditions can cause cracked bark near the base. This condition is easily corrected by giving the plant supplemental moisture.[图片]Dogwood Tree Bark is Peeling Due to Disease Dogwood anthracnose is a common disease in the Cornus genus. It causes yellow leaves and twig dieback, as well as sunken discolored areas of tissue. These are common symptoms of branch and crown canker as well. Basal trunk canker will cause splitting and some loss of bark. It also presents with lesions in the tree that weep sap and can seriously affect the health of the tree. It is best to consult an arborist for either of these diseases which cause peeling bark on dogwoods.[图片]Pests that Cause Tree Bark Flaking on Dogwood Dogwood bark peeling off may be the result of tiny insects that do more harm than good. The dogwood twig borer is a nasty pest that gets into the vascular tissue of the tree and undermines the tissue. It lives in the tree’s tissue and causes bark upheaval in infested locations. These invasive creatures may be difficult to detect until widespread damage is done because they hide away from investigative eyes inside the plant. Other borers, like the apple tree borer, also appear to favor Cornus trees and cause similar damage.[图片]Scale insects in high concentration may make it appear that the dogwood bark is peeling. This is because when they mass on a stem, they seem like hard-bodied scabs which can be easily flicked off with a fingernail. They have the appearance of damaged bark but are actually insects subject to pesticides and manual removal.

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2017年08月30日

The dogwood is a favorite ornamental tree with numerous seasons of interest. As a landscape tree, it offers flowering spring beauty, a fall color show and bright berries in winter. In order to get all these attributes at their peak, it is a good idea to apply fertilizer for dogwoods. But do you know when to feed dogwood trees, or how to fertilize dogwoods? Timing and know how are the key to success in everything. Read on for information to keep your dogwood looking its best.[图片]When to Fertilize Dogwood Trees Dogwoods are native to Eurasia and North America in temperate to warm regions. The plants are part of a classic landscaping scheme of natural deciduous trees and shade to partial shade understory plants. The delicate flower-like bracts liven up the garden and lead up to a festive display of colorful berries. Fertilizing dogwood trees in spring will produce good tree health and vitality to ensure the best displays. The key to useful plant feeding is to time it correctly. Fertilizing dogwood trees too late in the season might inadvertently cause a flush of new growth, which would be too sensitive to survive an early cold snap. The better idea is to feed the tree in early spring and again three months later. This will give the plant all the extra nutrients it needs during the growing season.[图片]Dogwood Tree Food The type of dogwood tree food is an important consideration too. New trees need a different ratio than established specimens. Dogwood trees need slightly acidic soil to thrive. Before you apply any fertilizer for dogwoods, it is a good idea to test your soil and see what nutrients it lacks and if the pH is suited to your plant. If the soil is not acidic, you can use an acid lover’s fertilizer suitable for such plants as rhododendron and holly. In most regions, a ratio of 12-4-8 or 16-4-8 will be sufficient. Such a ratio is higher in nitrogen, which is what the plant needs to form leaves and vegetative growth. That being said, too much nitrogen can limit the flowering in dogwoods.[图片]How to Fertilize Dogwoods Young trees should not be fertilized the first year, as they are too sensitive at planting and damage could occur at the root level. If you feel you must fertilize, use an organic tea, diluted to half. Once the tree is at least 6 feet tall, use ¼ cup of fertilizer in February to March, and feed again three months later. The granular form is useful and should be dug in around the edges of the root zone. Make sure you water well after fertilizing.[图片]Mature trees benefit from ½ cup per inch of trunk. You can also gauge the amount by figuring 3 ounces of fertilizer per every 1,000 square feet. Scatter the grains within 100 square feet of the tree and scratch into the soil. The adult tree’s root zone will go out that far from the tree and the wide area will have a better chance of delivering the food to the root system.

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2017年08月30日

The gray dogwood isn’t a tidy or attractive plant that you would want to plant in a well-groomed garden, but if you are planting a wildlife area or want a shrub for difficult conditions, it may be just what you need. Read on for information about this humble shrub.[图片]Gray Dogwood Information Gray dogwood (Cornus racemosa) is rangy and even a little scraggly, with suckers springing up all around it. The fall leaves are dark reddish purple, and while the color is interesting, you wouldn’t call it attractive. The white winter berries only last a short time and don’t add much to the appearance of the shrub. Although you may not want to plant it in a formal garden, it is right at home in a wildlife area or a location with poor, wet soil. As wildlife plants, gray dogwood thickets provide shelter, hiding places and nesting sites for birds and small mammals. Several species of birds eat the berries, including Eastern bluebirds, Northern cardinals, Northern flickers and downy woodpeckers. The flowers attract butterflies, and some species use them as larval host plants.[图片]Growing Gray Dogwoods Although you can grow it as a tree, a gray dogwood tree soon becomes a multi-stemmed shrub without constant attention in removing the suckers. Growing gray dogwood shrubs in a row provides a screen against unsightly views, strong winds, and harsh sunlight. Gray dogwood care is a snap too. The shrubs thrive in full sun or partial shade and almost any soil. They aren’t bothered by air pollution. These shrubs tolerate dry soil, so they seldom need watering, and never need fertilizer. The biggest task in caring for gray dogwood is keeping the suckers at bay. Pull them up whenever possible. If you have to cut them, cut at the source below the surface of the soil. Partially removed suckers soon return.[图片]Is Gray Dogwood Invasive? Any plant growing in its native range has natural controls to keep it in check, so native plants aren’t invasive. Gray dogwood is a native plant that is not considered invasive in any part of the U.S. In fact, it is recommended as an alternative to invasive shrubs such as non-native honeysuckle.[图片]Gray dogwood can, however, become aggressive in the landscape. It produces multiple suckers that become new stems. Over time, the shrub forms a thicket unless it’s thinned from time to time.

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2017年08月30日

There are any number of diseases and pests that can stress your dogwood and cause dogwood leaf drop. It is normal to see leaves falling in autumn but you should not see a dogwood tree dropping leaves in summer. When leaves are falling off dogwood in summer, it could mean a serious illness, improper siting or cultivation problems. Let’s examine proper cultivation and conditions for the trees and see what can be done about treating a diseased dogwood.[图片]Why Leaves are Falling Off Dogwood? Dogwoods are elegant, beautiful ornamental trees with several seasonal displays. Their oval to heart-shaped leaves deepen to crimson and orange in fall. The green leaves add charm and movement during the growing season and set a perfect backdrop for the bright flowerlike bracts. Dogwood leaf drop is not only an unsightly problem but it can spell doom for a plant due to reduced vigor. It is essential to determine the cause and preserve the energy gathering foliage. Dogwood plants need acidic well-drained soil in full to partial shade. Failure to provide these conditions will encourage disease and pest problems.[图片]Pests That Cause Leaf Drop Some of the most common pest causes of a dogwood tree dropping leaves are: Borer insects Scale Dogwood sawfly Insect pests are usually the easiest to diagnose. Borers leave piles of sawdust near the holes they make, scale is visible as little armored bumps along stems and sawfly larvae cause skeletonized leaves with whitish powder coating them. Borers and scale respond to appropriate insecticides while sawfly larvae are large and obvious enough to hand pick and destroy. Treating a diseased dogwood is a bit harder and requires correct diagnosis of the disease.[图片]Treating Dogwood Leaf Diseases Diseases of dogwood are the usual suspects when leaves are falling prematurely and include: Powdery mildew Leaf spot disease Canker Anthracnose One of the most recurring causes of leaf drop is powdery mildew. Many varieties of plants can get this fungal infection, which cause leaves to get a white coating and eventually suffocate and die. If a tree has a lot of powdery mildew, the overall health of the tree is affected due to minimized harvest of solar energy. Fungicides can be effective or you can prune out the infested areas. If the disease is a common problem in your area, it is best to choose a cultivar with powdery mildew resistance.[图片]Leaf spot disease also occurs on twigs and buds. It causes brownish tan spots on foliage, especially on shaded trees after heavy rains in the warm seasons. Prune out affected stems and leaves and destroy the plant material. Crown canker is a serious disease that will eventually girdle the tree, causing not only leaf drop but complete die back. The tree will need to be removed and destroyed.[图片]Anthracnose affects many ornamentals. It is characterized by purple spots on bracts and leaves in spring. Usually no treatment is necessary, but in severe cases, use fungicide at bud break. Follow with the spray every 7 to 14 days until all the leaves have opened.

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2017年08月30日

Autumn foliage aside, yellow leaves on a tree generally doesn’t signal health and vitality. The flowering dogwood tree (Cornus florida) is no exception. If you see your dogwood tree leaves turning yellow during the growing season, the tree is likely suffering from a pest, disease or deficiency. Read on to find out why your dogwood has yellow leaves.[图片]Avoiding Sick Dogwood Trees When delicate blossoms open on your dogwood tree boughs, you know that spring is on the way. This native tree grows wild throughout the eastern states, and it is also a popular ornamental. The small size works well in home gardens and backyards, but improper culture can cause sick dogwood trees. The best defense against pests or diseases attacking your dogwood is to provide appropriate care for your tree. This is easier when you understand that dogwoods are understory trees in the wild, growing in shade on organically rich soil. You need to provide a similar environment.[图片]Dogwood Tree with Yellow Leaves – Borer Attacks If your tree canopy dies back or the leaves turn fall colors prematurely, it may indicate a dogwood borer attack. This insect is the most common pest of the cultivated dogwood. Adult borers are day-flying moths that lay their eggs wounds or fissures in the tree bark. As the insect larva emerge, they bore into the tree, leaving holes and sawdust-like frass as evidence of their presence. Yellow leaves on dogwood trees can be an early sign of an infection. To prevent a borer attack, plant your dogwood in shade, not direct sun, and provide adequate irrigation to avoid water stress. Don’t weed whack close to the base of the tree or otherwise wound its bark, since wounds provide an entryway for the borers.[图片]Yellow Leaves on Dogwood Trees – Chlorosis Another possible cause of yellow leaves on dogwood trees is chlorosis. Dogwood trees are susceptible to iron chlorosis, which means that the trees are not uptaking sufficient iron to manufacture chlorophyll, the green pigment in leaves. You should suspect chlorosis if the yellow first shows up in the area between the leaf veins, leaving the veins green. In more severe cases, the entire leaves turn pale yellow.[图片]To prevent chlorosis in your dogwood tree, check the soil acidity before planting. Dogwoods cannot absorb the iron in the soil if it is too alkaline, that is, if the pH is above 7.5. While you are doing soil testing, check for magnesium, manganese and boron levels as well, since deficiencies in these minerals can also cause chlorosis. When you see your dogwood tree leaves turning yellow because of chlorosis, make sure you are watering appropriately. Overwatering the tree (or poor drainage) can also cause chlorosis. Likewise, root damage, girdling roots and trunk wounds all make it more difficult for the tree to transport nutrients.[图片]Dogwood Has Yellow Leaves – Other Issues If your dogwood has yellow leaves, the tree might also suffer from some other disease. For example, leaves with powdery mildew can turn yellow. Identify the disease by the white powder on foliage. Similarly, scale infection can also cause yellow leaves on dogwood trees. Scales are legless insects that look like small brown bumps on foliage or stems. Kill adults and eggs by spraying horticultural oil in spring.

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