Hosta plant leaves turn yellow or brown for a variety of reasons, including too much sun, not enough water, insect damage, disease or simply from going dormant in the winter. Making sure hostas grow in the right conditions, checking for insects and eliminating disease ensure bright foliage year after year.
Gardeners prize hostas for the wide variety of foliage shapes, sizes and colours. The perennial plants produce long, slender solid or variegated leaves in combinations of green, blue, gold and white, according to the Ohio State University extension service website. Considered easy to grow, hostas tolerate shade that other landscape plants do not. More than 2,500 types of hostas can be found in nurseries and garden shops.
Hostas grow well in United States Department of Agriculture (USDA) hardiness zones 3 through 8, which includes most areas other than deserts and subtropics, according to the University of Vermont extension service. Hostas' main requirement is a dormant period with winter temperatures below 4.4 degrees Celsius (40 Fahrenheit) for at least two months.
If an otherwise healthy plant starts to turn yellow, it may be due to receiving too much direct sunlight, according to the Georgia Hosta Society. Moving the plant to a shadier location will stop the leaves from burning.
Yellowing also occurs in drought conditions and ample watering should correct the problem. If the plant starts to yellow late in the season, anywhere from midsummer to the first frost, it could simply be starting to go dormant for the winter.
Changing types of hostas may solve leaf-yellowing caused by variations in sunlight, water and fertiliser. Some varieties tolerate full sunlight without their leaves yellowing, according to the University of Vermont extension service website.
Variegated hostas produce more brightly coloured leaves in sunlight. Blue hostas grow better in cooler climates while fragrant hybrids thrive in the longer growing seasons of southern states.
If growing conditions aren't the culprit, yellowing hostas may be infected with crown rot. Sclerotium rolfsii fungus causes rotting of hosta crowns, the area of the plant at and just beneath the soil level, according to the Iowa State University extension service website. Crown rot develops quickly in hot, humid weather. The fungus looks much like soil particles, but when it starts to attack a plant, it produces easily seen white strands across soil and the base of the plant. The strands release oxalic acid, a poisonous chemical that causes hosta leaves to rot and die. A leaf turning yellow from crown rot will easily pull away from plant. Crown rot usually only infects the plant's outer leaves, but the fungus can kill small plants, according to the Iowa State University website. The fungus can survive most winter conditions.
Hostas with crown rot should be removed from gardens and thrown away or destroyed. Identifiable fungus on the soil should also be removed and additional steps taken to stop the fungus from spreading: gardening shoes, tools, gloves and clothing should be washed or at least thoroughly rinsed before using in other areas. Dipping tools in a 10 per cent bleach solution helps prevent the fungus spread, according to the Iowa State University website.
Hostas produce lily-like flowers of lavender or white in midsummer. Some new hybrids produce upwards of 50 flowers, according to the Ohio State University website.
All varieties grow best in well-draining, rich organic soil or soil amended with additional organic matter such as compost or well-rotted manure. Hosta roots spread horizontally, requiring plenty of space between plants.
Slugs need to be controlled around hostas as they chew on the plant's leaves at night, according to the University of Vermont extension service website. Hostas also attract deer and voles.