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Friday - February 15, 2008

From: Vienna, Austria
Region: Other
Topic: Trees
Title: Is western soapberry (Sapindus saponaria var. drummondii) dioecious?
Answered by: Nan Hampton

QUESTION:

Hi! I found different information on the flowering habits of the western soapberry, Sapindus saponaria var. drummondii. Is it dioecious or polygamo-dioecious or none of them? I have some little seedlings growing, planning to use the fruits for soap in the future. so the flowering habits are important to know for me. How old must the western soapberry be to start flowering? Thanks!

ANSWER:

The mating system of Sapindus saponaria var. drummondii (western soapberry) is, indeed, confusing. Here are what the following sources say about it:

1. In "Manual of the Vascular Plants of Texas" Correll and Johnston say about the Family Sapindaceae: "...staminate and pistillate flowers on separate plants or often some flowers appearing perfect;..." They give no specific description for Sapindus saponaria var. drummondii.

2. In "Trees and Shrubs of the Trans-Pecos and Adjacent Areas" Powell says about the Family Sapindaceae: "Flowers small, unisexual, male and female on separate plants, or flowers perfect, borne in clusters,..." Again, there is no specific description for Sapindus saponaria var. drummondii.

3. In "Field Guide to Texas Trees" Benny Simpson says about S. saponaria var. drummondii: "Male and female flowers occur on separate trees, and in the deep sands of the Rolling Plains, groves of one to ten acres can be found that are apparently of only one sex. One or several trees spread vegetatively by rhizomes, creating these large groves. The clusters of white flowers produced in May or June must be inspected closely to tell whether the tree is male or female."

4. Information from the U.S. Forest Service says that S. saponaria var. drummondii is dioecious.

5. Finally, in "Forest Trees of Oklahoma: How to Know Them" Little says about Sapindus drummondii (syn.= S. saponaria var. drummondii): "Flowers many, almost stalkless, mostly male and female...."

So, I think you can probably expect your trees to be dioecious with either staminate (male) or pistillate (female) flowers, but don't be surprised if there are a few perfect (with both male and female parts) flowers scattered about on some of the trees.

Now, how long it will be until they bloom? This is another question we can't answer precisely. The U.S. Forest Service describes S. saponaria var. drummondii as being moderately slow growing and the Texas Forest Service Texas Tree Planting Guide describes its growth rate as moderate.

Here are a couple of quotes from the "Manual of Woody Landscape Plants" by Michael Dirr describing growth rate of trees:

"Rate of growth refers to the vertical increase in growth unless specified differently. Rate, as is true for size, is influenced by numerous variables such as soil, drainage, water, fertility, light, exposure, ad infinitum."

"The designation slow means the plant grows 12" or less per year; medium refers to 13 to 24" of growth; and fast to 25" or greater."

This, of course, doesn't answer when they might bloom. That, too, will depend on a number factors similar to those associated with growth. I would think, however, that it would be 4 to 5 years before they are as tall as 5 or 6 feet. They might possibly bloom by then. This is a lot of arm-waving, I know, but I'm afraid that's about the best I can do for you.