Hosta leaves turning yellow

Yellow Hosta Leaves – Why Are Hosta Plant Leaves Turning Yellow

One of the beautiful features of hostas are their rich green leaves. When you find your hosta plant leaves turning yellow, you know something is wrong. Yellowing leaves on hosta doesn’t necessarily mean disaster, but it is definitely time to investigate. The problem could be anything from too much sun to incurable diseases. If you want to find out why hosta leaves turn yellow, read on.

Reasons for Yellow Hosta Leaves

Hosta leaves turn yellow for a wide variety of reasons, and it is important for you to figure out the particular reason that applies to your plant.

Hosta Leaves Turning Yellow from Scorch

Perhaps the easiest situation to remedy is when yellow hosta leaves indicate too much sun. Hosta are plants that grow best in partial shade or even full shade. In fact, they are regular fixtures in the shade garden. If you grow them in full sun, you can expect yellow hosta leaves. The foliage turns yellow and scorches at the margins. When you see hosta plant leaves turning yellow because of too much sun, it is termed hosta scorch.

Hosta scorch is even more pronounced if the plant is also grown in poor soil. The plant prefers soil rich in organic matter that will hold water. During a drought, or when dried out in full sun, the hosta leaves become pale and the margins scorch. You can give the plant temporary relief by watering well early in the day, but the better and more permanent solution is to transplant the hosta to a shaded site in high organic matter soil.

Yellowing Leaves on Hosta Indicating Disease

When yellow hosta leaves indicate disease, the options for treating the problem are more difficult. When you see yellowing leaves on hosta, the plant may have petiole rot, caused by the fungus Sclerotium rolfsii var. delphinii. The earliest symptoms are yellowing and browning of the lower leaf margins. If you see brown, mushy decay and white fungal threads or fungal fruiting structures about the size of mustard seeds at the base of the petiole, your plant probably has this disease.

You cannot save plants infected with petiole rot. Prevent the problem by inspecting young plants carefully before you plant them. You should also remove and destroy all infected plants and remove and replace the soil to 8 inches.

Other fungal diseases, rots and virus diseases that cause yellowing leaves on hosta are equally impossible to cure. For fusarium root and crown rot, bacterial soft rot, hosta virus X and other viruses, all you can do is remove the plants and destroy them, trying not to spread the disease to other plants.

Since fungal diseases live in the soil and attack hosta at or below the surface of the soil, you may need to kill the fungus by solarizing the soil with black plastic. Be sure to keep your garden tools clean, keep the area free of debris, and avoid transplanting diseased plants. Other fungal diseases, such as root and stem rot, are generally caused by excessive moisture and are usually deadly. Be careful not to overwater and don’t limit air circulation by crowding the plants. Water your hosta at the soil level to keep the leaves dry.

Pests Causing Yellow Hosta Leaves

Foliar nematodes are microscopic worms that live inside the leaves. Symptoms, which are usually first noticed in June, begin as a yellow discoloration that later turn into brown streaks between the leaf veins. Keep an eye on the plant and remove affected leaves immediately to prevent the pests from spreading.

Hosta Leaves Turning Yellow Naturally

Once the growing season dies down, hostas will naturally begin to enter dormancy. When this happens, you may notice yellowing hosta leaves. This is perfectly normal and nothing to worry about. Once the leaves have completely died back in fall, you can cut the plant back.

Hosta Color Changes

Hosta ‘Remember Me’ in spring

Hostas have become extremely popular, due in great part to their wide spectrum of colors and variegations. Few other groups of plants have the same variety of foliage hues, which is important because foliage is the backbone of the landscape. Hosta leaves range in color from light buttery yellow to deep forest green to powdery blue, and a host of variegated forms are also available. Recently, hosta breeders have been breeding for red coloring in the stems and leaves.

One of the most fascinating things about hosta foliage coloring is that it often changes throughout the growing season. Some pigments lighten or brighten, while others become more green or chartreuse. These changes seem to be affected by heat, and indirectly by sunlight. Some change very quickly, while others are quite sluggish. The more heat to which a hosta is exposed, the faster the color change occurs. Plants changing the fastest seem to be those grown in a greenhouse in pots on elevated benches. Similarly, plants grown in southern gardens progress through the changes faster than hostas in northern gardens.

Hostas go through three main types of color changes

  1. Viridescent color change — The root word of viridescent means green, so a viridescent hosta becomes more green as the season progresses. It may start off yellow, chartreuse, whitish-green, and then darken to green.
  2. Lutescent color change — Hostas that are lutescent lighten as the season progresses. This may mean a shift from chartreuse to yellow or a shift from dark to light green.

    Hosta ‘Remember Me’ in summer after it has completed its color change for the season.

  3. Albescent color change — The word alba means white, and hostas that whiten from yellow or chartreuse to white are called albescent.

Blue hosta color is different because even though it looks blue, it is not actually blue. It is the waxy coating on the leaf surface which causes light to be reflected in such a way that the leaves appear blue. Depending on the amount of chlorophyll in the actual leaf, some blues can be very light and some can be much darker. Most blue-leafed hostas become green at some time during the growing season when their waxy surface is not as reflective as it once was. The wax seems to almost melt off with exposure to hot sun, harsh watering, or some pesticide sprays. Once the wax is gone, the same leaves will not regain their blue hue that year.To achieve the best blue leaf color in a hosta, select newer and improved blue varieties that have excellent waxy leaves. Plant them where they will receive ample indirect or lightly filtered light. Early morning sun is best in most regions, but it is most important to remember to keep the leaves protected from the sun during the hottest parts of the day. Take care not to rub the wax off the leaves by avoiding high pressure irrigation and petroleum-based pesticides.

To help you understand how hostas experience color changes, let’s look at some examples of a few popular varieties.

  • Hosta montana ‘Aureomarginata’ is an older variety that uses Latin in its name to describe its variegation. “Aureo” comes from the Latin word aureus meaning golden while “marginata” means margin. This would lead one to believe that this is a green hosta with a gold margin. Though it does exhibit a yellowish margin for a couple weeks in early spring, it quickly turns creamy white when the leaves completely unfurl. Often the margin lightens even further to white in summer. Thus you can see how the name ‘Aureomarginata’ could be deceiving.
  • Another springtime favorite is Hosta ‘Sea Fire’. As its name implies, this hosta is ablaze with color in the springtime. Just when the daffodils are blooming, ‘Sea Fire’ has emerged with nearly the same light yellow coloring. Few plants can rival its excitement as it emerges from a long winter sleep. However, as the warmer weather of summer approaches, its leaves turn from yellow to lush tropical green.
  • People familiar with the archetypal variegated Hosta ‘Gold Standard’ recognize the characteristic parchment gold center of its leaves. Amazingly though, its early spring color would not remind you of a plant named ‘Gold Standard’, for there is no gold to it at all when the leaves first emerge. Rather, the young leaves are green or chartreuse with a deep green margin. The golden color is not achieved until later in the season.
  • Another classic, Hosta ‘Undulata Mediopicta’, is described as having attractive green leaves with white centers. However, the heat of summer often causes the white center to darken, initially producing a green frosting or fogging and eventually darkening to all-green.
  • Hosta ‘Remember Me’ (pictured above) really requires two photographs to tell its whole story. When the plant emerges in spring, its leaves are bright gold surrounded by blue-green borders. By midsummer however, the center of the leaves brighten to ivory or near white. The change is so drastic that many people would not even recognize the plant if they were familiar with it only in one season.

Though not all hostas are chameleons, changing their leaf colors during the season, most are. Perhaps the only hostas that do not exhibit any kind of color change are those that are solid green. Perhaps this is one of the things that makes them so unique and explains why the thousands of hosta varieties are so fascinating and popular with today’s gardeners and collectors.

The leaves on several of my hostas have turned yellow, then brown, and finally collapsed onto the ground. What is happening to my hostas?

The hostas may have petiole rot. Petiole rot is a serious disease of hosta. It is caused by the fungus Sclerotium rolfsii var. delphinii. (Petiole rot can also affect daylily, peony, phlox, columbine, and other perennials.) Disease symptoms on hosta start as marginal yellowing and browning of the lower leaves. A soft, brown, mushy decay may be seen at the base of the petiole sometimes accompanied by white fungal threads. As the disease progresses, the leaves discolor and wilt. In the final stages of the disease, the bases of the petioles rot away and the leaves collapse and lay flat on the ground. Collapsed leaves pull easily from the crown of the plant.

The disease fungus produces small, round fungal fruiting structures about the size of mustard seeds that appear at the base of the infected petioles. These structures, called sclerotia, are a cream color when young, but gradually turn to a dark, brick red color. The sclerotia are long-term survival structures of the fungus. Sclerotia germinate during warm, humid weather and fungal mycelium grows in the ground until it finds a susceptible nearby plant.

Effective management requires a combination of strategies. Before planting hostas in the garden, carefully inspect each plant. Do not plant any suspect or symptomatic hostas. Remove and destroy infected plants. Also, carefully remove the soil in the area to a depth of 6 to 8 inches and replace it with non-contaminated soil. Avoid moving plants from contaminated beds to other parts of the garden. A mulch-free zone of several inches at the base of susceptible plants might also help. Common garden fungicides available at garden centers and other retailers are not effective.

Why Are My Hostas Turning Yellow?

Image by Flickr.com, courtesy of leezie5

Hostas are a shade perennial appropriate for use in non-tropical gardens and regions. It is a deciduous plant, losing its foliage in winter and resprouting each spring. Leaf yellowing can be caused by many factors, including too much sunlight, lack of soil moisture, infertile soils, soggy soil and the onset of winter dormancy.

Too Much Sunlight

In general, the hosta looks and grows best in partial to full shade light exposures, such as under the dappled to dense shade of trees. When sunlight is most intense, in the middle of summer, too much exposure can cause sunscald or leaf burn, the yellowing and browning of foliage. Over-exposure to hot sunlight causes leaf temperatures to increase and requires additional soil moisture to offset this imbalance. Usually the leaf dies rather than the hosta plant over-compensating and expending energy in maintaining the leaf in such an inhospitable environment. Through decades of hybridization and plant selection, hosta plant breeders have found some varieties that tolerate considerable direct sunlight exposures. These plants are an exception rather than the rule with hosta, however. In cool summer climates, full sun exposures on hosta can yield beneficial and presentable results. In regions with dry soil, arid air and hot summer temperatures, increased exposure to direct sunlight normally causes leaves to scald, yellow and die.

Dry Soil

If the hosta plant is exposed to dry soil or an exposed drought, the natural response will be to expend foliage in order to retain more water in crucial plant tissues, mainly the roots. Dry soils can cause the hosta to enter an early dormancy in an effort to weather the adverse conditions and hopefully re-sprout next spring when moisture is again plentiful.

Infertile Soil

If the soil is nutrient poor the hosta will have difficulty sustaining any plant growth. Sandy soils that lack any organic matter are particularly likely to cause scrawny or unattractive hosta plant growth. Moreover, soils that have been poisoned, such as being drenched with a petroleum product or herbicide, will also retard hosta growth. Lack of nutrients, specifically nitrogen, magnesium and manganese, is known to cause healthy leaves to become a sickly yellow color, too.

Soggy Soil

Hosta roots are not tolerant of soggy, waterlogged soils. Although they may withstand a rare, brief inundation of rainfall, standing water on the roots and stems of hosta leads to suffocation of roots and fungal rot problems.

Pestilence

An attack by insects or other pests can cause leaf yellowing. Insects that suck juices from foliage, such as aphids, can deplete leaves so they become yellow before dying. Snails and slugs are also known to relish hosta foliage, and although the rounded holes in leaves is indicative of their presence, they also may chew at leaf stems, causing the entire leaf to yellow.

Onset of Winter Dormancy

No hostas are evergreen. The are naturally programmed in their genes to become dormant in autumn when temperatures are cold and day lengths are short. Once autumnal frosts invade the garden, the foliage will yellow and die back to the ground. People in regions with mild, warm winters, such as in the subtropics, find that hostas are not long-lived, since they never experience the cold weather in winter to force the necessary winter dormancy.

Leaf Browning, Scorch, on Hostas and Other Shade Plants

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Brown leaf edges are common on hostas and other shade lovers when the temperatures rise or the sun is too intense.

Brown leaf edges, known as scorch, occur when the plant loses more water than is available or faster than the plant is able to absorb. Reduce the risk of this problem by growing shade lovers like hostas in shady areas free of hot mid-day and afternoon sun.

Add organic matter to the soil to improve the water-holding ability of fast draining sandy soils. Water the plants thoroughly and often enough to keep the soil slightly moist.

Mulch the soil with shredded leaves, evergreen needles or other organic matter to keep the soil cool and evenly moist. Yes, I know, this also creates the perfect environment for slugs. If a slug problem develops, capture these slimy pests with beer in a shallow can.

A bit more information: If slugs are a problem considering planting more slug-resistant hostas. These tend to have thicker leaves like the 2014 Hosta of the Year, Abiqua Drinking Gourd.

Throughout the hosta world plants like H. sieboldiana ‘Elegans’ are almost universally referred to as “blue” hostas. However, such plants are all technically, blue-green in color. When registering a new hosta, The American Hosta Society recommends that you use terms such as slightly blue-green, medium blue-green and intensely blue-green to identify this leaf coloration. Some references or catalogs may talk about blue, blue-green, gray and gray-green to describe these plants.

As mentioned before, all the species hostas are green. The difference here is that some hostas have developed a waxy coating over the green which reflects blue light. Thus, we see them as blue-green. If you rub the leaf of a blue hosta between your fingers and remove the wax, it will quickly show the green below.

The wax on the leaf surface is at its thickest and best in the cool of the spring. As the summer progresses, the heat of the sun and pounding rain, will cause the wax to wear off. Plus, hostas appear to produce less wax as the summer advances. So, by autumn, many “blue” hostas become green hostas. This doesn’t hurt the plant but, if you wanted the blue color to work as a complement to nearby yellow plants, you will lose that effect late in the year.

Hostas that develop a very thin covering of wax may lose it very early in the season. These plants end up spending most of the summer as green hostas and may be classified as either base color category (blue-green or green) depending on the reference or catalog.

Mr. PGC Comment: The blue-green cultivar H. sieboldiana ‘Elegans’ was developed in 1905 and has since become one of the all-time classics in the hosta world. At a recent meeting, I heard the hosta Registrar mention that around 400 new cultivars had been registered the previous year. Of those, over half had ‘Elegans’ in their background. There are a huge number of large blue hostas out there, folks!

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