UNITED STATES—Aridity is the opposite of humidity. It is why summer warmth is not as unpleasant here as in humid climates. It does not get so much consideration though. Most of the populace of California inhabits arid chaparral or desert climates. Aridity is so typical that any absence gets more attention. Humid warmth is both uncomfortable and relatively uncommon here.

Hurricane Hilary recently demonstrated how unusual humid weather can be here. It was merely a tropical storm as it left Mexico, but was significant nonetheless. Humidity briefly remained elevated after torrential rain in Southern California. It may have lingered longer in regions that lacked rain in Northern California. It caused warmth to seem a bit warmer.

This humidity would have been more horticulturally influential if it had lasted a bit longer. Obviously, irrigation is temporarily unnecessary for saturated landscapes. Some flooded. Some simply absorbed rain. Less obviously, landscapes that received no rain need a bit less water with humidity. Humid weather reduces evaporation from active foliar surfaces.

Humidity is both good and bad.

Humidity also reduces the volatilization of floral fragrance. Fragrant flowers are therefore more fragrant during humid weather. Delicate floral structures also last a bit longer. Many flowers are more turgid and colorful with humidity. All sorts of foliage, particularly tropical foliage and fern foliage, is more lush. After all, most vegetation is from less arid climates.

Humidity influences allergens also, both positively and negatively. Some allergens, such as fungal spores, are more abundant with humid weather. Some allergens, such as dust and pollen, are more abundant with less humidity. That is why humidifiers are helpful for dust or pollen allergies. It is also why dehumidifiers are helpful for fungal spore allergies.

Spontaneous limb failure can be another consequence of humid warmth. It is hazardous because it occurs very unexpectedly without wind. Warmth accelerates vascular activity, which increases foliar weight. Humidity with slow air circulation inhibits evaporation from foliage. If unable to shed enough weight, foliage becomes too heavy for limbs to support.

Highlight: Daylily

Each flower lasts for only a day. That is why the common name of Hemerocallis is simply daylily. Each floral stalk provides several flowers that bloom continually for several days. As one flower deteriorates, another replaces it. Because floral stalks shed so continually, they are not very practical as cut flowers. They are splendidly colorful in gardens though.

Most popular daylily cultivars are products of breeding that is too extensive to document. That is why almost all lack species names. Their cultivars names generally suffice. Most daylilies bloom for a month or so. Also, most bloom best for early summer. A few bloom a bit earlier. Some bloom as late as autumn. Some can bloom randomly or twice annually.

Daylily bloom can be yellow, orange, red, pink, almost purplish or combinations of these. Yellow or pink can be so pale that it seems to be almost white. Flowers can stand as tall as three feet, on bare stem. Their arching grassy foliage stays somewhat lower, in dense mounds. Most cultivars are evergreen. Some are deciduous. They propagate by division. Some migrate by vigorous stolons.

Tony Tomeo can be contacted at tonytomeo.com.