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Cultural Information

INTRODUCTION

Hostas are extremely popular, hardy herbaceous perennials which are grown primarily for their attractive foliage. They are easy to grow, shade-tolerant plants whose leaves come in a wide range of shapes, colours, sizes, and textures and may be solid in colour or variegated in different combinations of blue, green, white, and gold. The plants are low maintenance and are widely available from specialist nurseries and garden centres 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.

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 colour, 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.

Hostas change throughout the season as well as in their four to six year maturing process. Intensity of most leaf colours and variegation develops from early spring throughout the growing season. However, some plants produce their most distinctive colour in early spring and diminish as the season progresses. As a hosta matures, the height increases, leaf margins may widen, some may take on a more round leaf or develop a quilted, puckering appearance. It is possible you may not see some of these true adult characteristics develop for several years. Occasionally, they may produce sports of a different leaf colour or configuration from the original plant.

WHERE TO USE HOSTAS

Hostas look fine on their own as specimen plants or mixed into a perennial border, as background plants to add height, as ground cover or as edging plants. The wide range of sizes, leaf shapes, textures, colour and variegation all add to the seemingly endless design possibilities. Ferns, dicentras, carex, euphorbia and other fine foliaged plants make good companion plants with their delicate foliage. Shrubs, tall perennials and architectural obstacles that can be challenging are softened with the use of hostas. Use them to outline a pathway or encircle a tree trunk. Hostas are very popular with flower arrangers where the leaves are used to make a statement in flower arrangements.   [back to top]

SOIL PREPARATION AND PLANTING OUT

Hostas may be planted out at any time between the appearance of the new shoots in spring through to late summer while the soil is still warm thus enabling them to establish quickly before the onset of autumn. Whilst they can be moved successfully at the height of summer it is advisable to keep them well watered and to remove 80% of the leaves to prevent excessive loss of water. Never plant out hostas when they are dormant as there is a significant chance of the roots rotting.

Hostas are very tolerant plants and will prosper in a wide range of soils, however, one which is rich in organic matter, well drained and slightly acidic is ideal. The planting hole should be at least a foot deep and a mixture of grit and well rotted manure added will get the hosta off to an excellent start.

When planting out pot grown plants it is best to untangle and spread out the roots, shake off excess soil and plant at the same level as it grew in the container.

Hostas thrive particularly well in pots but they do require adequate drainage particularly small or miniature varieties. For miniature varieties we find a 5 : 1 mix of soiless compost to sharp grit to be ideal but for large hostas a John Innes No 2 mix with 10% added grit tends to work better and is less prone to drying out.    [back to top]

FEEDING

There are several choices of fertilizer, including liquid, granular, and slow release, and each has its’ benefits and limitations. 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. Any plant that is still producing new tender growth in late summer may lose that new growth to the first  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 early July.

Slow release fertilizers are best applied in early the spring and gently worked into the top layer of soil. Those extended release fertilizers, such as Osmocote®, 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 six months extended release fertilizer can be followed by an application of regular granular fertilizer in midsummer. When making up compost for potting up the addition of slow release fertiliser  can be very beneficial.

Liquid fertilizer can be used for both soil and foliar application and is typically 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.

All hostas benefit from a light mulching of well rotted manure in early spring but be careful not to cover the crowns as this can cause disease and eventually, rotting. The best time to mulch is when the first shoots appear and in that way you can be sure of avoiding the crown. If the compost or leaf mould is not well rotted you may be providing a perfect home for the hostas best friend – slugs!    [back to top]

WATERING

Water is important for optimal growth as hostas are natives of areas of high rainfall. 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. Whilst this short term lack of water is unlikely to kill the plant it can cause leaves to die back to the crown. Should this happen from spring to early summer, a good drenching will see new shoots appearing. This situation is seen most commonly in potted plants.   [back to top]

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:-

  • a) No shoots are growing from the centre 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.
  • b) When the hosta has outgrown the position it has in the border.
  • c) The hosta  has outgrown its’ pot and becomes difficult to water or shows signs of distress.
  • d) You wish to 'swap' cultivars with a friend!

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 or spade to make the divisions.

Early 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. Division of miniatures should be done with great care and only when the plant is well established.

Though spring division is easiest, summer division is preferred and can be done in July as 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.   [back to top]

HOSTA PESTS AND DISEASES

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 torch. Since some plants are more susceptible to slug damage, 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. We prefer to place pellets under a piece of slate near to the base of the hosta as this protects them from the rain and prevents them being picked up by pets. Most pellets today have an agent added which makes them unpalatable to children, pets and birds.  

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. What a waste of beer!

Other methods can be used, though they show limited success. Copper strips sold in garden centres may be used to surround plants particularly those grown in pots. The use of gritty materials such as chicken grit or crushed oyster shells scattered on the soil surface is also used. Gravel is not effective! 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. Salt will also kill slugs if applied directly to them.   [back to top]

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. Vine weevil larvae can be killed by the chemical prevention and elimination products are widely available from garden centres and are proven effective as a contact chemical.

FOLIAR NEMATODES

These 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.

CUTWORMS

These large soft bodied grubs, grey or brown in colour, are night feeding and feed on the buds and leaves of hostas. The easiest way of controlling this pest is by the application of a proprietary insecticide.

RODENTS

Mice and voles can wreak havoc in early spring on the emerging hosta shoots. Mice will nibble happily on the new shoots thus ruining the first leaves of spring. Voles on the other hand concentrate on the roots and have been known to kill even well established plants. Our solution is to use a combination of mouse traps and poison baits commonly available. Ensure all poisons are used and stored according to the manufacturers instructions.

VIRAL INFECTIONS

Hosta Virus X and other viruses are becoming more common in bare root hostas. When an infected plant is cut, the infected plant's sap can infect a healthy plant when the healthy plant is cut with the tool that was used to cut the infected plant. Precautions can be taken by disinfecting tools with bleach in between each cutting. Washing hands/gloves is also important. Above all, when an infected plant is discovered, it needs to be disposed of or burned. The virus can not live without a host plant. It is also important to learn the signs of a virus. Some images are available at www.hostalibrary.org to see the telltale markings. It seems that the Virus has been spreading more rapidly in our industry through bare root material. Much of the time the plants are dug in huge batches and the machines are not disinfected between each plant causing many plants to become infected in a short period of time. We have seen many examples of virus x in garden centres basically unnoticed largely through ignorance of the condition.  [back to top]