BLUE POTATO BUSH RARIN' TO GO WHEN OTHERS ARE FADING.

Byline: >JOSH SISKIN

As the dog days of summer come to a close, certain plants appear undaunted, as though they did not just live through some of the hottest weather on record.

Blue potato bush (Lycianthes rantonettii) is at the top of the list of inscrutable, late-summer horticultural wonders. This shrub currently has lost its head and gone into a fit of flowering madness.

"Head" is used advisedly since the patio tree form of blue potato bush is typically pruned to resemble the globe-shaped dome of a Tootsie Pop.

Although its foliage may lose color on and off during the year, the blue potato bush shows new life just when most plants have faded from the garden scene.

Other plants in the potato family (Solanaceae) are also blooming now.

Iochromas show tubular flowers in red, blue or purple. Cestrum elegans produces flared, bulbous tubes of wine red, pink, or violet, accompanied by handsomely cut, sea-green foliage. Brugmansias, also called Daturas or angel trumpets, ring in with numerous large, hanging and fragrant campanile bells in colors that include peach, pale yellow, gold, pink and white.

Another outstanding bloomer at summer's end is the cape honeysuckle (Tecomaria capensis). It gets its name from its habitat, the Cape of Good Hope in South Africa, and from its blooms, which have the swoop and extruding pistils of honeysuckle flowers.

Cape honeysuckle does best where it can grow wild without competition, such as on slopes where its aggressive roots prevent soil erosion, or against long fences or walls where a carefree vine is needed. The most commonly seen cape honeysuckle has orange to orange-red flowers but a yellow variety is also occasionally encountered.

Speaking of plants from the South African cape, blue plumbago (Plumbago capensis) displays a plethora of sticky, baby-blue flowers during the fall. This billowy shrub is commonly seen in freeway plantings and, like cape honeysuckle, will grow rampantly with a minimum of care.

Cupheas, all of which may be grown as colorful hedges, come into their own in early fall. The most popular is false or Mexican heather (Cuphea hyssopifolia), which makes a long- blooming low hedge 2 to 3 feet tall. It's usually seen with magenta violet flowers, but a white cultivar is also sometimes available. Mexican heather is promoted as a plant for either full sun or partial shade. Although the plant will grow in full sun, it does not look nearly as good as when it receives a half day of sun or less.

Mexican heather foliage is a fresh, clean and polished vibrant green, always looking as though it has just been hosed off or washed by the rain. Mexican heather will grow 2 to 3 feet tall. It can be used as a low hedge along walkways, in mixed perennial plantings or in containers.

Although Mexican heather is occasionally found on lists of drought-tolerant plants, its foliage is lusher and its flowers more plentiful when its soil is kept moderately moist.

Cuphea ignea, known as the cigar plant, has 1-inch, orange firecracker blooms and grows to a height of more than 4 feet. Cuphea micropetala has flowers that are similar to -- but twice the size of -- the cigar plant's and grows as tall as 6 feet or more. Cuphea llavea is a demure sub-shrub with flowers that resemble bats.

All cupheas need a good shearing every now and then. Otherwise, they become leggy and stop flowering.

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