Summer 2024

Tropical Style Plants for Summer Dry Climates

by Cynthia Engers

Many of us enjoy the look of plantings we may have seen on vacation and might like to grow some similar plants in our own gardens. Of course, we don’t live in the tropics or Hawaii, so it goes without saying that we can’t really duplicate a tropical garden in Contra Costa County. It is certainly too cold in the winter! And we generally look to save water and select plants that are low-water users.

So are we destined to enjoy ‘tropical-looking’ plants only on our travels? Not necessarily. There are many choices appropriate for our climate which, while not technically ‘tropical,’ might be seen as such.

Palms

Instead of the lush coconut palms of Hawaii, we can grow swaying queen palms (Syagrus romanzoffiana, Arecastrum romanzoffianum), pindo palms (Butia odorata, Butia capitata), fan palms such as the Mediterranean Fan Palm (Chamaerops humilis), various date palms and Brahea species (hesper palms), among others. All of these require little water in our area.  

For a full list of low-water using palms (and thousands of other plants) appropriate for our area, a great resource is the WUCOLS (Water Use Classification of Landscape Species) database (WUCOLS Database | California Center for Urban Horticulture UC Davis). If you are not familiar with WUCOLS, here is a little background information.

In 1991, the Water Conservation Office of the California Department of Water Resources initiated a project to “provide guidance to landscape professionals in selecting and maintaining plants based on their irrigation water needs.” At the time, while much research had been done on the water needs of agricultural plants and turf grasses, little had been done on the water requirements of landscape plants.

The project leaders divided the state into six climate regions and, for each region including ours (North Central Coastal) chose experts to classify landscape plants according to water needs, based on research available and the personal experience of the regional representatives. The result was a statewide classification of 1,200 species of plants by water need category: high, moderate, low, or very low, as well as unknown.

This research, which has since been expanded to include 3,546 different species and cultivars, is accessible to all via an online search tool at the link above. It is invaluable for guidance in selecting appropriate plants for our gardens.

What, then, can WUCOLS suggest for our tropical-look landscape? Still restricting our choices to low-water using plants, we find many interesting and attractive options.

Ferns and yuccas

For shadier areas, there are many ferns that require little water. These include the felt fern (Pyrrosia spp.) and silver cloak fern (Cheilanthes argentea). If we stretch our definition of ‘tropical’ to include desert tropical areas, we can add many spiky yuccas to our list. A particularly attractive one is Red Yucca (Hesperaloe parvifolia).

Other spiky choices

Poker plants (Kniphofia) as well as kangaroo paws (Anigozanthos varieties) are dramatic and exotic bloomers that often require minimal water in our area. It may be debated as to whether they look ‘tropical’ or not!

However, here are two truly beautiful, softer bloomers: Watsonia and Neomarica caerulea.

Watsonia is a bulb that hails from South Africa, where we can also find several other attractive choices for our tropical-style garden. Among the most dramatic species are Leucospermum (related to Protea) and Leucadendron.

More specifics about water use

In reading the section above introducing WUCOLS, you may have been thinking that our region is quite variable in climate, especially, from west to east. Even within Contra Costa County, we know that a plant in Brentwood will receive more sun and require more water than the same plant growing in Richmond. WUCOLS doesn’t categorize plants within parts of a region. However, the resource does qualify its recommendations in several ways:

1. It is assumed that a given plant is grown in full sun unless the species requires some shade to avoid injury, in which case it is evaluated for shade.
2. Plants are assumed to be ‘established,’ meaning that the landscape soil, rather than the root ball soil, is the primary source of water. This usually requires 2–3 years of development.
3. Because the categorization is subjective, the given ranking allows for users, based on their experience, to determine that a species needs somewhat more or somewhat less water in their area.
4. Two other factors contribute to water needs as well, the microclimate and planting density.

Given these qualifications, certain plants might be added to the ‘tropical’ list in particular situations. For instance, the bird of paradise plants, which are ‘moderate’ water users in our inland areas (Strelitzia nicolai and Strelitzia reginae) may be low water users near the coast or in a shaded inland area. Will we see as many blooms in the shade? Presumably not, but the foliage itself might be adequate for our satisfaction. Other plants with similarly large rather thick leaves, such as Chinese Yellow Banana (Musella lasiocarpa) could also be considered, as might a very attractive ‘tropical blueberry’ specimen called Dianella ensifolia.

In general, however, plants rated as moderate water users will require more water than we’d like to give plants in our dry-summer climate.

Finally, what does ‘low water’ really mean?

Fortunately, the WUCOLS project provides a mathematical calculation for translating the various water categories into inches of water per month. While it is beyond the scope of this article to go through the calculations, it is available for landscape professionals, as well as scientifically-minded home gardeners in this document: WUCOLSB.PDF (ucanr.edu)

For our purposes, the following information extracted from the document provides a guide. It displays the inches of water required in July for a healthy plant in different parts of the North Central Coastal region, based on the ranges provided in the WUCOLS database.

For the sake of comparison, a moderate water-using plant in Concord will require 2.8 to 4.2 inches of water in July, and a high water user will require 4.9 to 6.3 inches of water.

Conclusion

While it may be challenging to use tropical-style plants in our climate without using a lot of water, it is certainly possible, with some effort to find appropriate specimens. If you relish the tropical look, it may be worth the trouble to source them. It can certainly be enjoyable to add some exotic flavor to our home gardens.

Resources

WUCOLS Online Database WUCOLS Database | California Center for Urban Horticulture (ucdavis.edu)

WUCOLS Project document WUCOLSB.PDF (ucanr.edu)