Flora and Fauna News

Heavy Perfume Hits
Orchards and Neighborhoods

By Michael Plagens
Sonoran Desert Sciences

PHOENIX, Az. ----- The flowering season for cultivated citrus trees is under way bringing heavenly sweet perfume wafting through urban neighborhoods and orchards. The perfume is most noticeable after dark when temperature inversions trap it close to the ground. A temperature inversion occurs when a layer of warm air sets above a layer of cooler air.

Citrus trees are widely cultivated in Arizona below about 750 m elevation where hard winter frosts are infrequent. These climate requirements are very similar to those of the Ironwood, Olneya tesota, and so the presence of this native tree was a sign that it would be safe to put in citrus orchards. Many citrus orchards have been converted to housing tracts where some of the trees were left for the future residents to tend. Today, however, most developers bulldoze the trees completely leaving new residents to purchase new citrus cultivars available from nurseries.

Brittle Bush at Peak Blooming

PHOENIX, Az. ----- With warm temperatures and plenty of rain an abundance of bright yellow flowers of Brittle Bush blaze from xeriscapes along highways and around commercial buildings. With minimal drip irrigations these native plants have grown lushly verdant and have a bumper crop of flowers. This is one of the most widely used of the "natives". All too often landscapers choose instead exotic plants such as bougainvillea and oleander.

Brittle Bush can also be found blooming profusely, at the edges of paved highways. The extra water they get from runoff is adequate to grow and produce flowers. Brittle Bush sometimes support populations of insects such as aphids, beetles, insect larvae, and gall midges (small flies Cecidomyiidae). Thus Brittle Bush will provide food for insectivorous birds like hummingbirds, verdins and gnatcatchers. It is important not to spray pesticides onto the Brittle Bush or else you might poison the birds or at the least, eliminate their food supply.

Orange Blossoms are pollinated by Honey Bees (Apis melifera). Therefore, they do not release pollen in the air and do not contribute to hayfever/allergy symptoms.

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Brittle Bush, Encelia farinosa
Watercolor © Mike Plagens.