By T. Eric Nightingale, UC Master Gardener of Napa County

Finally, we have rain. While more determined gardeners may still be pursuing outdoor projects, I have set my sights on less-damp activities. Improving your indoor garden is a great way to spend a rainy day.

If you are like me, however, you are running low on places to put houseplants. One solution is to grow plants that need little to no soil.

Known as epiphytes, these plants have evolved other methods of obtaining the nutrients they need. Some accomplish this by absorbing much of what they need from the air, using specialized leaf structures called trichomes. Others have evolved to capture loose organic matter such as leaves dropped by taller plants. This organic matter decays in the plant's personal “compost pile” and provides the epiphyte with the nutrients it needs.

Classic epiphytes include orchids, bromeliads, anthuriums and a few types of ferns. Houseplant lovers would recognize the common, most easily cared for species of these plants. They have been a fixture of the houseplant section of garden centers for many years.

If you are new to growing epiphytes, these plants are the place to start. One example is Phalaenopsis, or the moth orchid. Species of this genus are the orchids most often seen in stores and homes. Compared to more finicky orchids they are easy to care for and bloom regularly.

You may also recognize bromeliads from the Aechmea genus. They are large-leaved, urn-shaped plants with dramatic blooms arising from the center.

Anthuriums are popular around the holidays, as their bright red, shield-shaped flowers contrast nicely against their green leaves.

Once you have mastered these popular epiphytes, investigate some less-common options. Orchids come in innumerable sizes and shapes. Some of them I find so mesmerizing that I have difficulty walking away.

Many people choose to grow epiphytes in pots filled with loose, airy bark. But there are a few other ways to make creative use of available space. Epiphytes are easily secured to boards of attractive wood, with some sphagnum moss placed around their roots. This construction can then be mounted to a wall like a piece of art. Attaching an orchid or bromeliad to a piece of driftwood or grape trunk is a great way to make a table centerpiece.

Recommended care for these plants varies, so research the exact species that you have. Generally, orchids and anthuriums prefer to be watered once a week. Use only as much water as needed to wet the medium around the roots and let it dry completely between watering.

Most bromeliads like water poured into their cup-shaped center structure. Keep the cup full but drain and refresh it about once a month.

Air plants (Tillandsia) are another low-maintenance houseplant option. Like bromeliads, to which they are related, most air plants are epiphytes, living their lives anchored to another plant. A few are known as aerophytes. These have almost no roots and will roll freely around their native desert sands.

Tillandsia are native to North and South America and cannot tolerate cold temperatures. Most also do not thrive in full sun in summer but can tolerate the cooler sun of fall and winter. Like many houseplants, they prefer bright, filtered light. Their long, thin leaves covered with fine, water-collecting fuzz give them an artistic look that makes them ideal for home decor. Their blooms are stunning pink or purple flowers that pop against the grey-green foliage.

Air plants can live almost anywhere in the home, as they do not need soil. I place mine on top of books on my bookshelves and on end tables. I have also used florist wire to secure them to the sides of shelving and railings, as well as to the trunks of some of my larger houseplants.

If your living space is generally cool and humid, your air plants will need watering less often than in a hot, dry home. Some people keep their air plants in globes or terrariums. These are stylish and also increase the amount of humidity around the plant, reducing the need for frequent care.

Most homes are fairly dry due to air conditioning. Air plants in an air-conditioned environment should be watered two to three times a week. Simply collect your Tillandsia and drop them into a bowl of water. Leave them in the water no more than 15 to 20 minutes. Shake excess water from between the leaves. Water in the crevices can promote rot if it does not evaporate quickly. For that reason, I usually leave my air plants upside-down in a dry location for at least an hour. If your plants do not dry out completely within four hours, they will eventually rot.

Tillandsia rarely need fertilizer. If you suspect your plants do need a feeding, you can find appropriate fertilizer at most garden centers. It is sold in small containers, as it should be applied conservatively, no more than once a month.

The UC Master Gardeners of Napa County are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website (http://napamg.ucanr.edu) or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.