The differences between the hoya and hosta plants are numerous, and perhaps the most confusing aspect is sound and spelling of their names. Hoya plants (also called wax flowers) are tropical climbing shrubs that are usually grown as houseplants while hostas (called plaintain lilies) are herbaceous perennials grown outdoors in regions where winters are cold. Worldwide, there are over 200 different species of hoyas and 70 species of hosta. Plus, there are hundreds of cultivated varieties of hostas that are grown in gardens in temperate climate regions.
Based on the flower structure as well as arrangement of veins in their leaves, the plants are not closely related. Taxonomists place hoya in the milkweed family (Asclepiadaceae), although many now dissolve that family within the dogbane family (Apocynaceae). Hostas are in the lily family (Liliaceae).
All the species of hoya plants are native to coastal bluffs, stream edges, escarpments and rain forests across the subtropical and tropical areas of Asia, Australia and some Pacific Islands. Hostas grow naturally on the cliffs, rocky riverbanks, and woodland and alpine meadows in northeastern Asia from China northward into Siberia.
Hoya plants bear oval, thick and often leathery green leaves in opposite pairs on their woody stems or vines. Their flowers are trumpet-shaped and held in flat or rounded clusters. Each blossom is a tube with five waxy petal lobes with a hooded crown of stamens. The flowers range from white to red-pink in color. Hostas bear large, thin leaves directly from the ground and range in color from green to yellow-green or blue-green. Often they are heart- or lance-shaped. The flowers occur on tall stems in loose arrangement and range in color from white to lavender. The individual flowers are either funnel, bell- or spider-shaped.
Hoya plants grow best in fertile, moist but fast-draining soils, responding well to frequent watering in the heat of the spring and summer months. They tolerate very bright indirect light to full sun with some shading in the hottest part of the tropical afternoon. Depending on species, hoya plants should not be exposed to frosts, although some Himalayan species can tolerate and survive temps as low as 20 degrees Fahrenheit, according to the "A-Z Encyclopedia of Garden Plants."
Hostas also appreciate a soil that is fertile and moist and has good drainage so the soil is never waterlogged after rain. They look and grow best in partial shade exposures, receiving direct sun rays only in the morning and then shade from trees the rest of the day. Too much sun and dry soils can cause foliage to yellow and scald. Hostas must have a winter dormancy with prolonged and consistent temperatures below 20 to 30 degrees Fahrenheit.
Hoya plants can be grown outdoors in cool-winter but frost-free landscapes in a variety of applications--a mixed shrub border, as cover for a trellis or fence, or in a hanging basket or patio container. They also grow as houseplants extremely well. Conversely, hostas are outdoor garden plants only, since they need the winter cold dormancy for a long life. They are prized as ground-cover perennials in woodland gardens and shaded foundation beds; they are not grown in subtropical or tropical gardens at all.