动态第775页 - 绿手指 - 养花技巧、花生病了怎么办、花园打理和设计

2017年09月14日

A reader from Charleston, South Carolina wrote in to say, "My Southern magnolia (Magnolia grandiflora) has yellow leaves. Is it dying?" The reader had had this balled-and-burlapped specimen for two years; it had been 5 feet tall when installed.[图片]More specifically, this Charleston resident complained of not only sparse flowering in the tree's second spring, but also -- and more worrisome to this gardener -- "yellow leaves in fall that drop off of the tree" (note that this species is evergreen). So what could be the cause of this? Possible Reasons Why a Southern Magnolia Has Yellow Leaves First of all, you need to rule out a nutrient deficiency in your soil. Yellow leaves on Southern magnolias can indicate that your soil has insufficient nitrogen. The only way to determine for sure whether or not this is the problem is to have a soil test done. If the test results do, in fact, show a nitrogen deficiency, you can fertilize accordingly to raise the nitrogen level. The nitrogen content of a fertilizer is indicated by the first number in the NPK sequence, which should be printed somewhere on the fertilizer bag.[图片]Let's assume that you have had a soil test done and have been able to rule out nitrogen deficiency. What else could be the problem? Sometimes, when Southern magnolia trees develop yellow leaves (often accompanied by the presence of spots), it is only as a prelude to natural shedding (which happens periodically). However, this seems to occur more often in the spring. With the reader reporting seeing the yellow leaves in fall, it makes one think there could perhaps be a problem with her Southern magnolia in terms of water and/or drainage. Let's expand on that observation. Too much or too little water are both possibilities, whether you irrigate yourself and/or rely on rainfall.[图片]But the issue of water is inextricably intertwined with that of drainage. Why? Because even if there is sufficient water, if it percolates through the ground too rapidly, the Southern magnolia tree would not be able to take full advantage of it. Conversely, if the drainage is impeded by an overly clayey soil, and you get a lot of rain and/or overwater your specimen, the roots will "drown." Either extreme is bad news. If you think drainage is an issue, you may want to transplant your tree to another area, after first preparing the soil for optimal drainage. A loamy soil is ideal.[图片]Growing Information for Southern Magnolia Trees Popular in the American Southeast, to which region these plants are indigenous, Southern magnolia trees are best grown in USDA plant hardiness zones 7-9. Grow them in full sun to partial shade. Since they like fertile soil, ideal growing conditions would include a soil enriched with compost. They like a soil pH that is on the acidic side.[图片]These trees are classified as broadleaf evergreens. They can grow to be as high as 80 feet tall. The fragrant flowers are white. Bloom time is late spring. Even the cone-like structure left over after flowering is attractive; it can be as much as 5 inches long. If you live in the North and wish to grow a Southern magnolia, look for 'Bracken’s Brown Beauty,' a cold-hardy cultivar, which is suitable for all the way up to zone 5b.

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2017年09月14日

What do yellow leaves mean on Rose of Sharon plants that you're watering well? Perhaps you're watering your rose of Sharon plants too well! [图片]Over-Watering is as Bad as Under-Watering Over-watering plants is an extremely common problem, and one of the signs is yellow leaves (when they should be green). The roots of plants not tolerant of waterlogged soil won't be able to "breathe," and they die of a lack of oxygen. Ironically, after the roots "drown" in this manner, you'll see the "drying up" of the leaves because the now debilitated roots won't be able to make use of all that water.[图片]Drainage is Key You may truly think that you're not over-watering; but if your soil isn't well-drained, the roots still could, in fact, be resting in waterlogged soil. If your case is, indeed, a case of poorly-drained soil, your best recourse would be to transplant the rose of Sharon plants to an area where the soil is well-drained. Prepare the area now, in the summer (peat moss can be mixed into the soil to improve drainage), and do the transplanting in autumn, once the weather cools off.[图片]Why Only Some Plants are Dying Are some of your plants thriving while others are showing yellow leaves and dying out? What seems a 'random' dying out might not really be so, at all. Let me draw an analogy. In a group of 20 people who smoke tobacco, some might die of cancer in their fifties, others might do so in the seventies, and still others might live to a ripe old age without becoming cancerous.[图片]We aren't all alike, and even folks with very similar genetic makeups are subject to different environmental influences. To some degree, the same is true of plants. For all you know, the rose of Sharon plants that have survived till now may have gotten off to better starts as 'babies' and are simply a bit more resilient than those that have already died from the over-watering.

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2017年09月14日

I've gotten a few questions over the past week or two from readers who have noticed white, fuzzy mold growing on their seedlings. This is a fairly common issue for those who start their own plants from seeds. Most of us plant our seeds and take care to keep the seedlings moist, but that can cause the white fuzzy mold to appear on them.[图片]There is good news for your seedlings--and your garden, too. The fungus itself is not going to hurt your seedlings. The bad news: that fungus is a sign that your soil is too wet. Soil that is too wet can result in having the delicate roots of your seedlings rot, which will eventually result in plant death.[图片]How to Stop White Fuzzy Mold on Seedlings Luckily, the mold is an easy thing to fix. Chances are, you are causing the mold by watering too much. Don't water your plants-to-be unless the seedlings really need it. It is easy to get into a routine of just giving them a quick water every day or so "just to be sure," but this can sometimes do more harm than good. Check the soil's moisture with your finger; only water if the soil is dry. That simple check can help you stop the white fuzzy mold from growing. [图片]Rethink how much you water when you do water. You may simply need to cut down the amount of water you put on each seedling--another way to reduce white fuzzy mold for healthier seedlings. Another thing that can help kill off the mold and prevent it from growing is to increase the air flow around your seedlings. You can do this by having a fan running nearby for at least a few hours a day. Not only does this help prohibit fungal growth, but it also results in sturdier seedlings. Additionally, you may want to look at how much light the seedlings are getting. They need at least twelve hours of good, strong light per day to grow well.[图片]That also helps the water to dissipate and not sit stagnant. Try not to place them in direct sunlight, either, because covered trays can get too hot and damage the seedlings. Check the temperature, too. The best photosynthesis occurs when the temperature stays between 77°F and 82°F). Finally, if at all possible, consider a system that lets you water from the bottom of the seedling container. This not only encourages the roots to grow deeper. It also helps alleviate mold and fungus because the surface of the soil is not constantly moist, so it cannot grow. Once you do one or all of those things, you can actually remove the white mold from your seedlings. Gently scrape it away with a knife or spoon.

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2017年09月14日

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2017年09月14日

"How do I treat ants and sooty mold on a magnolia tree?" asked one reader recently. It is a common query. His question continued as follows: "We have a four-year-old magnolia tree (4 inches in diameter and 13 feet in height) that has really never looked great but has always had nice white flowers in spring, at least. The leaves never got that real dark green look. Now, this summer, the leaves have started looking a lighter green and the bark has mold on it.[图片]I have washed the mold off the bark and noticed at the base of the tree the bark is coming off about 4 inches up. I pulled the loose bark off, and under it there was a ton of ants. The layer of bark under that is still solid, but a few bore holes (the holes only go in a little bit, I think). We are in Florida." Problems With Sooty Mold and Ants Actually Stem From Scale Insects The ants and mold (it is probably the mold called "sooty mold") may be the effect, rather than the cause of your magnolia tree's problems. The real cause may be magnolia scale bugs. The scale insects secrete a liquid named "honeydew" that invites sooty mold. And because this honeydew -- true to its name -- is a very sweet substance, the ants like to feed on it. You can find information on organic ant control in a separate resource.[图片]What Is Sooty Mold? "Sooty mold" sounds disgusting, and it has an appearance to match. It appears as a sickly, black film covering the bark and/or leaves of a plant. Known in scientific lingo as Capnodium, sooty mold is a kind of fungus. As the University of Florida Extension points out, the sooty mold fungus, in and of itself, does not cause a direct problem for your plant, but rather an indirect one: namely, it inhibits the photosynthesis in a plant.[图片]Photosynthesis is the very important process whereby the leaves of a plant convert nutrients into carbohydrates, by harnessing the energy derived from the rays of the sun. With a layer of sooty mold fungus covering the leaves of a plant, the sunlight cannot get through properly. The result is that the necessary photosynthesis can't take place, and the health of the plant suffers accordingly. Scale insects are commonly the culprit behind this chain of events on magnolia trees. To fight these insects effectively, learn how to practice magnolia scale control. Other sucking insects also secrete honeydew, including: Aphids Mealybugs Whiteflies[图片]Take careful note that it is the sucking insects, rather than the sooty mold fungus or the ants, that you should be fighting. The fungus and the ants will go away once you have eliminated the sucking insects.

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2017年09月14日

Leaf tip browning is an annoying condition that commonly affects certain types of houseplants. Spider plants, tropical plants, and those with long, strappy leaves are especially susceptible. The main difficulty when confronting leaf tip burn is to remember that it's a symptom of a larger problem (usually a cultural issue), as opposed to a condition in itself. So once your plant has burned leaf tips or margins, there's no way to reverse the damage at that wounded location.[图片]The only thing to do is correct the underlying problem and hope the plant continues its healthy growth. The other problem with a leaf-tip burn is figuring out which of the possible factors may be causing it. Is it the water? Your fertilizer habits? The humidity? You might not know right away, so the best idea is, to begin with, the most likely condition, change it to the extent possible, and wait to see what happens. If new growth is unaffected or the scorching stops, you've figured it out. If it continues, then move on to the next condition and work on that.[图片]Ideally, you'll catch leaf-tip burn early enough that the plant's appearance won't be completely ruined. These are the factors that can potentially cause leaf-tip burn: Watering issues. Leaf scorching can be a sign of erratic or insufficient watering or low humidity. It is especially true for tropical plants, which dislike the parched conditions in most centrally heated homes in the winter. These plants are evolved to luxuriate in humidity levels that range between 60 and 100 percent in their rainforest homes. A winter-time home can easily go to 20% humidity, which can cause leaf scorching. The solution is to raise the humidity—mist the plants, use a pebble tray, or relocate the plant to an area with higher humidity such as the kitchen or bathroom. Also, remember that plants with strappy leaves have a greater challenge to move water from the roots to the ends of the leaves, so these plants are likely to show leaf-tip scorching faster than plants with shorter leaves. Finally, if you suspect your water is highly alkaline (a pH above 7), consider finding a more neutral water source. Plants prefer a slightly acidic environment.[图片]Fertilizer issues. Fertilizer salts can cause leaf scorching, especially if large doses are fertilizer are applied. If you notice scorching on your plants shortly after feeding a heavy dose of fertilizer, it might be a problem with your fertilizer. Flush the soil with clean water several times to remove accumulated fertilizer salts and be more careful in the future. Fluoride. The idea that fluoride can damage houseplants has taken off recently, but the truth is that fluoride damage is usually limited to plants in the Dracaena family. These plants are susceptible to fluoride damage over the long-term, so if you're experiencing leaf burn in a Dracaena species, switch to un-fluoridated water. If the plant isn't dracaena, it's unlikely that fluoride is the issue.[图片]Cold damage. Closely related to water stress, many houseplants aren't acclimated to cold, drafty conditions (by a winter window, for instance). Cold damage often shows up in the extremities first, meaning the leaf margins and leaf tips. If your tropical plants suffer from leaf scorching during the winter months, try to raise the temperature (and humidity, most likely) around them. Sun damage. Sun damage usually shows up as yellowing of the whole leaf, or even scorched spots on the leaves. Nevertheless, if your plant has recently been subjected to a change of direct light it's receiving, this could be the culprit.[图片]Chemical damage. It is less likely to result in leaf-scorching, but it's possible. Household pesticides and cleaning chemicals can burn plants in some cases, so be aware of what you're using on your plants. Ultimately, a leaf-tip burn is almost always a cultural problem—fungal and bacterial diseases are typically more widespread across the leaf surface and usually involve the stem as well. So the best way to correct leaf-tip burn and margin scorching is to ask what cultural conditions might be causing the condition, then making an effort to fix them.

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2017年09月14日

What Is Azalea Leaf Gall? First of all, let's consider what a "gall" is, in general, in the context of horticulture. A gall is a tumor-like eruption in plant tissue. A number of different plants are susceptible. The two types of plants upon which I most commonly find galls are: Oak trees Goldenrod A gall represents the plant's reaction to damage caused by an invading agent. In the case of azalea galls, that agent is a fungus (see below). But there are other agents that cause galls to develop on other plants. For example, one master gardener has written about the leaf galls caused by insects on various trees.[图片]Regarding azalea leaf galls, specifically, you will notice two different phases (which may be present at the same time on the same plant, as in my picture): In phase one, the swollen leaf tissue is waxy and most often pale green. In phase two, it is a gray blob (and more recognizable to the beginner as some sort of fungus). Even the flowers on azalea bushes can be infested with galls.[图片]What to Do About Azalea Leaf Galls First of all, take solace in the fact that their bark is worse than their bite. As alien-looking and repulsive as azalea leaf galls are, they are not considered overly serious. They are caused by the fungus, Exobasidium vaccinii. Pick off the leaves where the azalea leaf galls occur and dispose of them properly. Do not put them in the compost bin, and do not leave them lying around on the ground, lest the fungus spread to other branches.[图片]For preventive care, avoid letting the soil become compacted around your azaleas. You can accomplish this in a number of ways, including by: Working ample amounts of humus into the soil Applying landscape mulch around the plants Furthermore, as is usually the case when dealing with fungus prevention, make it a point to apply water to your azalea shrubs down at ground level, rather than spraying from above. The latter practice gets the foliage all wet, which is an open invitation to fungi. Having said all that, overall, I have found the amount of time I need to put into azalea care to be relatively minimal here in the Northeastern U.S. Care has consisted mainly of occasionally spraying neem oil on my Gibraltar azalea to kill aphids.

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2017年09月14日

Many homeowners who landscape their properties with trees are taken aback when they spot infestations of leaf gall on their favorite specimens. Appearing as little bumps on the foliage of a tree (as if your plant were breaking out with some weird type of acne), these disfiguring eruptions look terrible. But how bad are they for the long-term health of your plant? And what is the cause behind them?[图片]What Causes Leaf Gall? How Big a Problem Is It? "We have a river birch tree which is about three years old," writes one reader. "Suddenly this summer, small bumps are appearing on some of the leaves. Is this a disease and can it be stopped?" What this reader is reporting is a case of leaf gall. Those small bumps are caused by an insect that eats or lays eggs on the plant's foliage. One Master Gardener explains that the gall "is the plant's response to the resulting irritation," drawing an analogy to what happens to the human body after a bug such as a mosquito bites us: a bump is left behind. She notes that, while galls are rarely fatal, "they may cause early leaf drop," but she adds that a healthy, mature tree will be able to cope with such leaf drop by producing new foliage and that a serious problem should only result if the galls keep coming back for several years in a row.[图片]What's the Solution? The bad news is that, once you spot these bumps, the damage has already been done. You can't spray to get rid of the bumps that are currently infesting your tree's foliage: you are stuck with them for the present year. As the same source notes, however, if leaf gall is a recurring problem for you, you can spray in early spring to get a jump on the insects. However, do note that you can't just spray willy-nilly: the spray that you use must target the particular insect that is causing the leaf galls to form.[图片]One problem with spraying, however, as pointed out by the Missouri Botanical Garden (MBOT), is that you will be killing beneficial insects, too -- insects that may actually be able to help you control your leaf-gall problem over the long haul (by killing the insects who cause the galls). They emphasize that spraying is a preventive measure, and that a certified arborist should be employed for the job (because it takes great skill "to identify the gall-producing organism").[图片]The good news, again, is that leaf gall is typically not considered very dangerous (either in general or to river birch trees, specifically). In fact, MBOT asserts that a leaf studded with these ugly growths is still "usually able to carry out photosynthesis at near normal levels." In addition to birches, trees known to be susceptible to developing leaf galls include: Elms Maples Oaks

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2017年09月14日

Have you ever picked up a leave that was dotted with bumps or had long protrusions dangling from it? Chances are these are leaf galls.[图片]What are Leaf Galls Leaf galls are a frightening sight, but are not usually as serious as they appear. These bumps and deformities are usually the result of feeding by insects or some other foreign organism such as bacteria, fungi, mites, nematodes, and even viruses. These organisms are usually not still on the plant leaf. The gall itself is actually the plant’s response to the irritation. It’s not unlike the bump you get when an insect feeds on you, expect the leaf gall is not going to go away.[图片]Despite appearances, the insect is not living in the gall. In fact, it is very likely that once you notice the galls the insects have moved on. Before they do, they can do a lot of cosmetic damage to many plants and in particular trees. Galls can also form on stems and flowers, however leaf galls seem to be the ost prominent and get the most notice. It is the fresh new growth that are attacked by the insects and other organisms and then produce the galls. Mature leaves are rarely affected. However many common trees are susceptible to leaf galls, especially when first leafing out in the spring. Maple, oak, elm, hackberry and others each are favored by a different insect that causes unsightly and intimidating galls.[图片]Damage will be greater following a mild winter, since more insects have survived and are hungry. Galls won’t usually kill a tree, but they may cause early leaf drop. A healthy tree will send out new growth and recover. What Can You Do About Leaf Galls? Since the damage occurred before the gall formed, treatment is rarely recommended. If you have a serous reoccurring insect problems, you can spray your tree in early spring, to lessen the severity of the damage. Contact your local extension office for specific guidelines and recommendations in your area. But if you're patient, nature may take care of the problem for you. Gall making insects tend to attract their own predators.[图片]One way leaf galls can cause a serious problem for trees is that their formation requires energy and nutrients from the tree, which can stress and weaken the tree itself, as it is coming out of dormancy in the spring. This can happen when there is an unusually high concentration of galls on the plant or when the plant is attacked and galls are produced several years in a row. For this reason, you should not ignore the presence of galls entirely. If this is the case, you should consider finding out what organism is causing the galls and treat for it the following spring, to prevent further stress and damage.

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2017年09月14日

Readers email me all of the time during the cold-weather months to ask, "Why is my arborvitae turning brown?" In fact, I witness the phenomenon frequently, myself while driving around during the cold New England (USA) winters and observing people's landscapes. As common an issue as this is, I felt that it deserved the article that follows, to help homeowners understand: The nature of the problem (that is, the reason for so-called "winter burn").[图片]How to prevent it. Or, failing successful prevention, what to do about it, should it occur. The Reason Why Arborvitae Foliage Turns Brown If your arborvitae shrub turns brown, it could, depending on the time of the year, be due to a problem known as "winter burn." Did it turn brown over the course of the winter or early spring? Then winter burn is, indeed, likely to be your problem. What is it all about? Well, the combination of wind, sun, freezing temperatures, and lack of available water in winter can cause arborvitae foliage (and the leaves of other evergreens, as well) to turn brown, due to so-called "desiccation" (which means drying out). Water is the lifeblood of foliage. When an evergreen shrub can't draw water up through its root system to its leaves during periods when the ground is frozen (at which time any moisture in the soil becomes unavailable, as nature "shuts down"), those leaves -- beset by challenging conditions, as it is -- give it up their green color.[图片]They have been killed by winter burn. How to Prevent Winter Burn (or Deal With It If It Has Already Occurred) So how do you prevent arborvitae leaves from turning brown? And if browning does occur during the cold weather months, what action, if any, should you take once spring returns? I will begin with five prevention tips: Protect with tree wrap (picture) Select a sheltered location at planting time Water in late fall Water during thaws Mulch over the root zone[图片]Regardless of the type of arborvitae you plant, your best bet for avoiding winter burn is to wrap the arborvitae in burlap. Placement in the landscape can also help prevent browning: avoid planting arborvitae on the south side of a wall (the sun can be an enemy in winter) or in an area exposed to high winds. Many experts recommend easing up some on watering arborvitae in September to encourage hardening off, then maintaining adequate irrigation from October until whenever the ground freezes in your area. Such an irrigation regimen will help prepare the shrubs for winter. Also look for opportunities to water your arborvitae during the winter. You have probably heard the term, "January thaw," right? If the ground thaws out at some point in the winter (thaws can happen in February, too), take advantage. With the soil loose again thanks to the thaw, any water you spray on the ground can permeate down to the plant's root zone once again. This drink could help your shrub in the same way that a glass of water slakes the thirst of a wanderer in the desert.[图片]As a final preventive measure, you will want to apply garden mulch around your arborvitae. Remember, winter burn is a moisture issue, at bottom. And mulch helps conserve moisture in the soil around a plant. So it is a no-brainer to mulch your shrub if you are concerned about the possibility of winter burn.[图片]Arborvitae branches whose foliage turns brown (entirely) due to winter burn may not come back, but there is no sense in being hasty about pruning (you never know), so I would hold off on pruning until well into the spring or even summer. Only time will tell as to whether your arborvitae branches will recover from winter burn; there is not much you can do to reverse the damage that results in brown foliage. Instead, direct your efforts at preventing winter damage in the future (see above). If green growth does, eventually, re-emerge on a branch damaged by winter burn, prune the branch back as far as that greenery. But if the arborvitae branch never shakes the "brown look," just prune if off entirely.

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