As summer descends upon us, many of us are drawn to tropical plants. With the increasing heat of summer we are left with only pleasant memories of spring daffodils, sweet peas and delphiniums. The sun is now high in the sky and both the day and night temperatures are almost unbearable for many garden plants. This is the time for tropical plants.

Surprisingly, it is the nighttime temperatures that are most important to most tropical plants. This week the nighttime lows in our gardens were a balmy 63 to 65 degrees. It is these mild night temperatures that trigger our tropical plants to grow and flower.

The warm summer months are the best time of year to plant and enjoy the lush flora of the world's tropical regions, like the Amazon basin, tropical Africa, the Caribbean and Southeast Asia. Most coastal gardeners can get just about any tropical plant to survive for a season or two. But a bit of homework, combined with some thoughtful plant selection and a bit of adventure will result in a tropical garden that thrives, flowers and prospers.

In recent years plumeria has become synonymous with tropical gardening. Named varieties are now finally available. Unfortunately, many curious gardeners were introduced to plumeria by the unnamed, un-rooted offerings of transient vendors at local fairs and swap meets. A decade later many of these plants have yet to bloom. Would you buy a rose simply labeled "yellow"? Of course not, so why buy a "yellow" plumeria?

Like rose bushes or apple trees, some plumeria will bloom well here along the coast. But, there are also plumeria varieties that will not bloom in our area. Shop wisely. Next month in this column I'll discuss plumeria in more detail

Most Brugmansia, or Angel's Trumpet, are even more fragrant than plumeria and nearly as popular. Growing wild on the slopes of the Andes, Brugmansia perform best in a climate that mimics their mountain origins. In the Amazon basin, daytime temperatures and nighttime temperatures show little variation. But on the slopes of the Andes, warm days are followed by cool, crisp nights. Often the temperature change from day to night is 30 or 40 degrees. Without this day-night temperature fluctuation many angel's trumpets bloom poorly.

Cannas, sometimes called Canna Lilies, arrive in our gardens from the warm regions of Central and South America and are among the easiest tropical plants to grow. Generally tall, vertical plants with green, bronze or variegated leaves, Cannas bloom abundantly, usually with clear red, yellow, orange or apricot flowers. My favorite selection is a unique multicolored hybrid called Cleopatra, with both yellow and red flowers and foliage on the same plant.

Cannas have only three requirements; lots of sunlight, lots of water and lots of nutrition in the form of nitrogen. Unfortunately, a disease known as canna yellow mottle virus has swept rapidly through California in recent years and infected thousands of plants. Many cannas have been left with mottled leaves and stunted or disfigured growth.

But there is no need to limit your tropical garden only to the popular hibiscus, philodendron and giant bird-of-paradise. Even plumeria, Brugmansia, canna and bananas only scratch the surface of exotic possibilities.

As you might expect by now, my favorite tropical addition to a local garden is a rare and illusive plant. Sometimes called brick and butter vine, Thunbergia mysorensis is considered by many to be the most beautiful vine in the world. Growing wild in the tropical mountains near Mysore, India, the brick and butter vine is a stunning tropical plant; a "must-have" for any passionate gardener who has seen it. Fortunately for us, it is easy to grow in our coastal Orange County gardens.

An evergreen vine, the exotic, spectacular yellow and reddish-brown flowers hang in abundant 2- to 3-foot long strands, usually dozens at a time. This is an incredible vine when trained high along a pergola or patio cover where the dangling flowers drip down like a golden waterfall.

Each flower is filled with sweet nectar that will attract every hummingbird in the neighborhood. Although most vines bloom only seasonally, brick and butter vine will bloom year-round in our area. As evidence, a plant growing in the tropical area at Roger's Gardens has never been without flowers in four years!

Coral Fountain (Rusellia equisetiformis) is a weeping shrub adorned with hundreds of firecracker red flowers nearly year-round. If deep, rich blue is your color, try Thunbergia battiscombei from tropical Africa or Blue Ginger (Dichorisandra thyrsiflora) from the jungles of Brazil.

Also from Brazil, Bloodleaf (Iresine herbstii) offers the brightest red foliage of any of the thousands of plants I have grown. The bright purple-red foliage and stems of this leafy plant are eye-popping, and I wouldn't be without it in a tropical garden.

In our gardens, summer's heat is reflected in the bright reds, oranges, deep blues and yellows of tropical plants. As summer descends upon us, why not create your own tropical paradise. Now is the time.

* RON VANDERHOFF is the nursery manager at Roger's Gardens in Corona del Mar.

ASK RON

My one year old Haas avocado has dropped its leaves and appears to be going to seed. What's wrong?
JERRY
Costa Mesa

Without seeing the whole plant and asking several more questions, I can only speculate about what is going on. Nevertheless, there is a strong possibility that your young avocado has a root disease called Phytophthora cinnamomi, often referred to simply as root rot. Avocados need a mineral based soil that is incredibly open, porous and well-drained. A proper planting site and proper planting techniques are critical to success with an avocado tree.

The other possibility is sunburn. Young avocado trees have very few leaves and their green stems will burn quite easily in the summer sun. Eventually, when the tree becomes larger it will develop enough of a canopy to shade its tender branches.

You will probably need to stop by a nursery and discuss your tree and its symptoms in more detail with a knowledgeable horticulturist.
-- Ron Vanderhoff, the Coastal Gardener

ASK RON your toughest gardening questions, and the expert nursery staff at Roger's Gardens will come up with an answer and publish it. Please include your name, phone number and city, and limit queries to 30 words or fewer. E-mail stumpthegardener@ rogersgardens.com, or send to Plant Talk at Roger's Gardens, 2301 San Joaquin Hills Road, Corona del Mar, CA 92625.