Houseplants for the dark and the dry

The indoor life can be challenging for many houseplants.  Temperatures may be mild, but most houseplants suffer from a lack of light.  A bright windowsill, especially in Arizona, can overwhelm many plants with light and heat, but away from the window, or in light filtered by blinds or drapes, the light intensity drops off quickly.

The human eye is a poor light meter.  Our eyes adjust to light in our environment by allowing more light in to our eyes while in dim surroundings, and letting less in while in bright situations.    The eye then, offers a poor gauge of light intensity with its constant compensation.

But light is of premier importance to plants.  Light is their energy source.  While fertilizer is sometimes called “plant food,” fertilizer is the equivalent of vitamins to plants.  Light is the true source of energy they use.  An indoor plant may often be observed to bend or reach out towards its far away source of illumination.  This is a growth response which positions leaves and stems to intercept the maximum amount of light.

Most houseplants have been selected for tolerance of low light situations.  Many come from the forest floor in tropical forests – dimly lit sites with the moderate temperature we enjoy.   But these habitats are usually moist and humid.  The plant selection must be narrowed further to those plants which tolerate low light and also can withstand the dry air of an indoor environment.  A tolerance for dry soil due to forgetful watering is also a plus.

These parameters narrow down the list of good houseplants considerably.  We want a plant with the low-light tolerance needed for the forest-floor, and the adaptation to dryness we see in a cactus.  Such plants may be found among the desert adapted Gasterias and Haworthias.  These plants come from South Africa, Madagascar, and the Arabian Peninsula.  They are related to Aloe plants.  While adapted to desert or dry tropical conditions, these plants specialize in the shaded habitats found under shrubs or on cliff faces.  They are small plants, which also works well for life indoors.

Gasterias have thick leaves adapted for water storage.  The leaves can be quite tongue-like in appearance - smooth, sometimes crinkly, and usually dark green.  The leaves are often speckled or mottled with spots or zones of white to yellow.  They are not grown for their flowers, but they will flower with red blooms on a tall stalk if they are healthy and mature.

Haworthias are more varied.  Many have leaves which are an interesting dark green, sometimes approaching black.  Some have white to yellow ridges or patterning on the leaves.  Others are low-growing star-shaped plants which hug the soil.  The flowers are drab.  These plants are grown for their interesting leaves.

Gasterias and Haworthias grow slowly, which is to be expected for plants operating with low light and little water.  The commonly available species are good plants to position near a sunny window, or on a windowsill if it is not blasted by sunlight.  When well grown, both Gasterias and Haworthias are prone to making pups, small plantlets, around their base.  These may be separated and grown as new plants.

Southern Arizona’s favorable climate allows Gasterias and Haworthias to be grown outdoors.  But the plants are too small to serve as landscape plants.  Many have a sensitivity to winter cold.  These plants have reason to be happier indoors, if well cared for.  They are popular as houseplants around the world.