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Hosta. Hostas. Funkia.

Introduction

Hosta (syn.: Funkia) is a genus of about 23–40 species of lily-like plants native to northeast Asia. They were once classified in the family Liliaceae but are now included in the family Agavaceae by the Angiosperm Phylogeny Group. The scientific name is also used as the common name; in the past they were also sometimes called the Corfu Lily, the Day Lily, or the Plantain lily, but these terms are now obsolete. The Japanese name Giboshi is also used in English to a small extent. The rejected generic name Funkia, also used as a common name, can be found in some older literature. Taxonomists differ on the number of species; as such, the list at the right may be taken loosely. The genus may be broadly divided into three subgenera. Interspecific hybridization is generally possible, as all species have the same chromosome number (2n = 2x = 60) with the exception of H. ventricosa, a natural tetraploid that sets seed through apomixis. Many varieties formerly described as species have been taxonomically reduced to cultivar status, while retaining Latin names resembling species (e.g., H. 'Fortunei').

They are herbaceous perennial plants, growing from corms or rhizomes, with broad lanceolate or ovate leaves varying widely in size by species from 3–40 cm long and 2–30 cm broad. Variation among the numerous cultivars is even greater, with clumps ranging from less than 10 cm across to more than 2 m across. Leaf color in wild species is typically green, although some species (e.g., H. sieboldiana) are known for a glaucous waxy leaf coating that gives a blue appearance to the leaf. Natural mutations (sports) of native species are known with yellow-green ("gold") colored leaves or with leaf variegation (either white/cream or yellowish edges or centers). The flowers are produced on an erect panicle up to 80 cm tall; the individual flowers are usually pendulous, 2–5 cm long, with six tepals, white, lavender, or violet in color and usually scentless. The only strongly fragrant species is Hosta plantaginea, which is also unusual in that the flowers open in the evening and close by morning. This species blooms in late summer and is sometimes known as "August Lily".

Cultivation and uses

Though Hosta plantaginea originates in China, most of the species that provide the modern shade garden plants were introduced from Japan to Europe by Philipp Franz von Siebold in the mid-19th century. Newer species have been discovered on the Korean peninsula as well. Hostas are widely-cultivated ground cover plants, particularly useful in the garden as shade-tolerant plants. Hybridization within and among species and cultivars has produced numerous cultivars, with over 3000 registered and named varieties, and perhaps as many more that are not registered yet. Cultivars with golden- or white-variegated leaves are especially prized. Popular cultivars include 'Francee' (green leaves with white edges), 'Gold Standard' (yellow leaves with green edges) 'Undulata' (green leaves with white centers), 'June' (blue-green leaves with creamy centers), and 'Sum and Substance' (a huge plant with chartreuse-yellow leaves). Newer, fragrant cultivars such as 'Guacamole' are also popular. Pictures of hosta species and cultivars, along with other information, may be found at http://www.hostalibrary.org.

The American Hosta Society and the British Hosta and Hemerocallis Society support Hosta Display Gardens, often within botanical gardens.

Hostas are notoriously a favourite food for deer, slugs and snails, which commonly cause extensive damage to hosta collections in gardens. Poisoned baits using either metaldehyde or the safer iron phosphate work well for the latter, but require repeated applications. Deer control tends to be variable, as anything other than fencing tends to work for a few years then cease to work as they become accustomed to it.

Foliar nematodes, which leave streaks of dead tissue between veins, have become an increasing problem since changes in attitudes about pesticides since the mid-1990's in many countries have caused a resurgence in this once-controlled pest. There are no effective means for eliminating nematodes in the garden, although they can be controlled to the point where little or no symptoms are seen.

A virus called Hosta Virus X has become common since 2004 and plants that are infected must be destroyed. It can take years for symptoms to show, so symptomless plants in infected batches should also be considered infected.

Otherwise they are generally easy and long-lived garden plants, relatively disease free, requiring little care other than watering and some fertilizer to enhance growth. Some varieties are more difficult to grow, as can be expected with 5,000+ cultivars, but most are easy enough for beginners.

Hostas are extremely popular, hardy herbaceous perennials grown primarily for their beautiful foliage. They are easy to grow, shade-tolerant plants. Leaves come in a wide range of shapes, colors, sizes, and textures and may be solid in color or variegated in different combinations of blue, green, white, and gold. The plants are low maintenance and are widely available in nurseries and garden centers. Many catalogs also offer a large selection of hosta plants, with more than 2,500 different cultivars on the market. Hostas originally came from Japan, China, and Korea. They were first introduced to Europe in the late 1700s and then came to the United States in the middle 1800s.

Plant Size and Shape

A hosta plant generally reaches full maturity in 4–8 years, and its size depends on the cultivar. Cultivars are "cultivated varieties" that have been developed for some desirable or improved feature such as plant form, size, bloom, leaf color, variegation, pest resistance, etc.

The miniature Hosta 'Baby Bunting' grows to only a few inches in diameter, while other cultivars reach 8 feet wide and even larger. Hosta 'Blue Angel' and 'Sum and Substance' are examples of very large plants that need to be given ample room to grow. Most hosta plants develop a rounded shape, although some cultivars have a vase shape, which is maintained as the plant grows larger. A few hosta cultivars are rhizomatous and can spread by underground rhizomes or runners.

Leaf Color

Hosta leaves may be a solid color such as blue, green, gold, or yellow. The blue color is actually a green leaf coated with a wax that makes it appear blue. The wax tends to "melt" from the leaf following exposure to sun and the heat of summer. Variegated leaves may include a combination of lighter and darker shades of color in the leaf. "Medio variegated" leaves show a light color in the center of the leaf, which may be white, gold, yellow, or light green. "Marginally variegated" leaves show a light color on the edge of the leaf.

Some plants also show seasonal foliar changes. A plant that exhibits "viridiscence" will change from light colors in the leaf early in the growing season to all green leaves as the season progresses. "Lutescent" leaves will change from green to yellow, and "albescent" leaves will turn from yellow to white. Leaf color may also be affected by the amount of sun the leaves receive.

Leaves that are thick and stiff are termed "rugose" or are said to have "heavy substance"; such leaves are considered to be somewhat resistant to slug feeding.

Flowers

All hostas bloom in summer with spikes of lavender to white, lily-like flowers, which can be quite showy. New cultivars of hosta plants are also being bred to produce larger and even more attractive flowers. Some newer plants may have 50–75 blooms on each flower scape. All fragrant hosta flowers are hybridized from Hosta plantaginea, which has 6-inch long, beautiful, white fragrant flowers.

Shade/Sun Requirements

Hostas are considered shade-tolerant plants, but most do not thrive if grown in deep shade. Hostas grow best in an exposure with morning sun and afternoon shade. Some cultivars will tolerate some afternoon sun, although plants grown in full afternoon sun (especially variegated plants) will show signs of marginal burning on leaves in the summer months.

In general, the blue-leafed hostas require shade, while the gold, yellow, and white-leafed hostas can tolerate more sun. Fragrant hostas grow best with 5–6 hours of daily sun. Morning sun with some early afternoon sun helps the fragrant blossom to develop. A few examples of sun tolerant hostas are Hosta plantaginea, 'August Moon', 'Fragrant Bouquet', 'Guacamole', 'Fried Green Tomatoes', and 'Sum and Substance'.

Companion Plants

Companion plants enhance the appearance of a planting of hostas. Early blooming bulbs and perennials are especially nice with emerging hosta leaves. Spring bulb foliage can be hidden after blooming by the larger hosta leaves. Recommended companions include snowdrops, crocus, tulips, daffodils, trillium, anemones, and forget-me-nots. Ferns, hellebores, pulmonarias, and wild gingers are also nice companion plants. In summer months, bright annuals such as impatiens, begonia, and coleus make attractive companion plants.

Soil Preparation

Hostas will grow best in rich organic soil. A loamy soil type may not need the addition of organic matter, but few of us are so lucky to garden in ideal soil and will need to add organic amendments. The recommended soil is well drained, has a slightly acidic pH, and is enriched both with nutrients and organic matter.

When making a new hosta bed, many gardeners like to cultivate to a depth of 12–16 inches. Apply 6 inches of organic matter and till it into the new bed. Materials such as compost, leaf mold, well-rotted manure, Canadian peat moss, composted pine bark, and municipal sludge products such as Milorganite® and Com-Til® may be used. The addition of organic matter will also serve to raise the bed, which will improve drainage for the plants.

The ideal pH range for hostas is 6.5–7.5, which is slightly acidic to slightly alkaline. In higher pH soils, the addition of organic matter such as Canadian peat moss and cottonseed meal will tend to lower the pH.

The planting hole should be dug at least a foot deep. The width of the hole should be one and a half times the expected mature size of the clump. Check the plant's label for ultimate size, or ask a nursery for information. Most hosta roots will grow and spread horizontally, so a large, wide hole is best.

Planting

Remove the plant from its container and loosen and untangle the roots. Occasionally, the plant may be root bound in the container; if so, tap the sides to loosen the roots from the pot. If the roots are difficult to loosen, it may be necessary to cut through some of them, making several vertical cuts in the rootball. Shake excess soil from the roots, and do not use it in the planting hole. Place the plant in the hole at the same level as it grew in the container. The area where the leaves and roots meet should be at ground level.

Hostas ordered from mail order catalogs may arrive as bare root plants. Soak the roots in tepid water for about 30 minutes prior to planting. Form a small cone in the bottom of the hole, spread the roots over it and add the amended soil. Water the plants well following planting.

Fertilizer

There are several choices of fertilizer, including liquid, granular, and extended release granular, and the gardener will want to weigh the benefits and limitations of each. Follow label directions carefully for the application rates of each type of fertilizer. Be careful not to apply fertilizer on top of or on the new growth, eyes, or leaves of the plant. All fertilizer applications should be discontinued by late July in Ohio. Any plant that is still producing new tender growth in late summer may lose that new growth to the first fall frost. Hostas need a hardening period prior to cold weather.

A balanced granular fertilizer such as 10-10-10 or 5-10-5 can be applied early in the spring, followed by an application six weeks later, followed by a midsummer application. Timing of these applications would typically be early April, mid- to late May, and mid-July.

Extended release fertilizer is applied early in the spring. Extended release fertilizers such as Osmocote® or Sierra Blend® are rated for three, six, or nine months release times. However, heat and moisture may shorten the longevity of release. An early spring application of three or six months extended release fertilizer can be followed by an application of regular granular fertilizer in midsummer. Liquid fertilizer is used for both soil and foliar application. It is applied every 7 to 10 days according to the fertilizer label instructions.

Following are some comparisons of the amounts of nitrogen, phosphorus, and potassium in fertilizer. The three numbers displayed on the fertilizer container are the percentages of nitrogen, phosphorus, and potassium (N-P-K) content, always listed in this order. Granular fertilizers with an analysis of 5-10-5 or 10-10-10 are recommended for hostas; these fertilizers have a ratio of 1:2:1 and 1:1:1. Organic fertilizers, such as compost or manure, typically have low analyses and are slow release; they are better used as organic soil amendments than as fertilizers.

Many gardens do not need additional fertilizer if a soil test shows the soil has sufficient amounts of the necessary nutrients. In this case, an addition of compost over the bed once a year, applied in the fall, is usually sufficient.

Water

Water is important for optimal growth. A minimum of an inch of water each week is recommended, and can come from rain, irrigation, or hand watering. Hostas that are grown in sandy soil may need even more water because of the increased drainage provided by the sandy conditions. In general, the greatest growth occurs when water exceeds the minimum recommended rate. Watering hostas on a regular basis early in the day is highly recommended. The soil should also be checked to make sure runoff is not occurring. A deep watering will ensure good root development.

Occasionally, a plant will show symptoms of inadequate water. Leaf tips will show burning. This occurs because the leaf tips are located the furthest from the roots, and the tip is showing stress from inadequate amounts of water. Drooping leaves may also be caused by inadequate moisture.

Propagation and Division

Propagation of hostas is easily achieved by dividing existing plants. Hostas do not come true when planted from seeds, with Hosta ventricosa being the one exception. Most home gardeners will propagate hostas by division.

Division should be done when no shoots are growing from the center of the mature clump and this bare area detracts from the appearance of the plant. Division of the clump will improve the plant's appearance. Lift the entire hosta clump and wash the soil from the roots, if possible, to make it easier to see where to cut to divide the clump. Cut with a sharp knife to make the divisions.

Spring is the easiest time to divide plants because new shoots are only a few inches high and the leaves have not expanded. Be careful not to overdivide hostas in spring; divide only the fast growing hostas then. Do not divide the sieboldianas or the Tokudamas in spring. New roots will not grow until the foliage has fully expanded and hardened off. During this period, the leaves may desiccate quickly on warm days, since the roots have been reduced in size or were injured during division. A hot day may cause injury such as leaf burn, but this is probably not permanent damage.

Though spring division is easiest, summer division is preferred and can be done in August, at least 30 days before the first fall frost date. Warm soil and higher humidity at this time promotes better root growth, and plants may put on a little growth spurt at this time.

Keep newly divided plants well watered for the first two weeks, especially if there is a period of drought. Some of the larger leaves on a division may be cut back to reduce water loss. Frequent division of a clump will restrict plant and leaf size, and keep it from developing to its desirable mature features.

Hosta Pests

Slugs and Snails

Slugs and snails are nocturnal foragers and are the most common pest of hostas. They eat small round holes in the leaves. By beginning an abatement program early in the spring, slugs may be easier to control. Look for silvery slime trails in garden beds to determine if slugs are present. They may be spotted during daylight hours or in the evening by using a flashlight. Since some plants are more susceptible to slug injury, check around those particular plants to detect slugs. Thin-leafed hostas and those with leaves growing close to the ground are most susceptible to slug injury. Chemical slug pellets and baits that contain metaldehyde are widely available commercially, however label directions must be followed carefully. A new product came on the market in 2000 that shows some success in slug control; it contains iron phosphate, which is less toxic to animals and birds than baits containing metaldehyde. Beer traps are widely used, albeit only moderately successfully. Place a small shallow container, such as a jar lid, level with the soil and fill with beer. Slugs are attracted to it, crawl in, and drown. Other methods can be used, though they show limited success. Copper strips sold in garden stores and catalogs may be used to surround plants. The use of gritty materials such as diatomaceous earth scattered on the soil surface is also used. Other traps may be made by laying wet newspapers on the ground overnight. Check beneath these the next day to find slugs that have taken refuge from heat and sun. Kill the slugs by dropping them into a 10–20% solution of ammonia and water. Salt will also kill slugs if applied directly to them.

Insects

Black vine weevil adults chew irregular notches on the edges of hosta leaves. The black vine weevil larvae that feed on the crown and roots, however, do the most serious damage; symptoms of injury include yellowing and wilting of foliage. Foliar nematodes are microscopic-sized worms that can infest hosta leaves. Nematodes overwinter in the ground and move to the leaf where they feed between the veins. The symptom is a brown streak that appears between the veins in late July or August. Foliar nematodes are a new problem, and to date, current research has not found a way to eradicate them.

Deer, Rabbits, Voles, and Squirrels

Deer can eat all your hosta plants in one evening, leaving just the stalks standing. Ten-foot tall fencing and trained guard dogs are the only reliable method to keep them out of the garden. Gardeners also use deer repellant, a bitter-tasting chemical that is sprayed on the leaves. These products need to be re-applied after several rainfalls. Motion detector garden sprinklers have also been used with some success. Rabbits occasionally eat young shoots in the spring, and sometimes bite off flower scapes. Squirrels will eat hosta leaves during a drought, and sometimes dig up plants. Voles chew on the roots of hostas, and a heavy infestation of voles may kill plants. Wire cages made of hardware cloth encircling the hosta roots may deter them.

Diseases

Virusare of concern and are an emerging and important issue in growing hostas. Symptoms include an irregular mottling of the foliage, yellow ringspots, or small yellow dots or flecks on the leaves. If a virus is present, the plant(s) should be discarded and tools used in the hosta planting should be disinfected. If there is a specific need for diagnosing viruses in a hosta plant or planting, contact your state university's plant and/or pest diagnostic lab to discuss the testing procedures and fees that are involved.

Other problems may show up as chemical damage, cold or frost damage, sunburn, and "melting out" of the leaf. These problems are not infectious.

Picture photo Hosta Hostas Funkia