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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Sunday - May 20, 2012

From: Austin, TX
Region: Southwest
Topic: Non-Natives, Shade Tolerant, Trees
Title: Trees for shade in Austin
Answered by: Barbara Medford

QUESTION:

I live in Austin and I am looking for a good tree to plant under a large live oak I have in my backyard. Something slow-growing of course and, the garden only gets late day sun for about an hour. Filtered sun only before that. I have always liked the Japanese Maples but wonder if they will survive the heat or maybe you have a better suggestion(s). Thank you!!

ANSWER:

First things first: no planting of any tree now. We recommend that woody plants, trees and shrubs be planted in cold weather, from November to January, when the plants are dormant, and less likely to be damaged by the process of planting.

Second, planting anything under a live oak would be dangerous to both the incoming tree and the live oak. Damaging the live oak in the process of planting could leave it open to being infected with disease. And being planted under an oak will be two strikes against the incoming plant. 1. Oaks are capable of allelopathy, whereby they emit substances to discourage competition beneath them. These substances can be in the bark, the leaves or the soil. 2. An hour of sun is not going to sustain any tree, most need sun (6 hours or more of sun a day or part shade (2 to 6 hours of sun a day).

On the subject of Japanese maples, they are (surprise) native to Japan, as well as North and South Korea, China, Mongolia and Russia. From East Texas Gardening, here is an article Japanese Maples by Keith Hansen of the Smith County Extension Office. Here is an excerpt from that article: "East Texas has great conditions for growing these Asian beauties – much more favorable than the rest of the State. Our normally sufficient rainfall, acidic soils, and definite 4 seasons combine to provide great conditions for growing one of the most exotic groups of ornamental trees." That part about sufficient rainfall and acidic soils doesn't sound much like Austin, does it?

The Lady Bird Johnson Wildflower Center is dedicated to the growth, propagation and protection of plants native not only to North American but to the area in which they are being grown. The reason for this is conservation of resources. You can purchase a non-native plant, spend a great deal of time and money fertilizing, watering and treating for disease and still watch the plant die.

We are going to go to our Native Plant Database and, using the Combination Search, will search on Texas, low soil moisture, height of 6 to 12 ft, and shade under Light Requirements, just to see what kind of result you might get. There were exactly two:

Hamamelis virginiana (Witch hazel) - USDA Plant Profile map showing this only grows in a few counties in far southeast Texas

Ilex verticillata (Common winterberry) - USDA Plant Profile map, one teeny-tiny spot in Orange Co. Texas on the southeast Gulf Coast.

So, scratch that. You might consider, if you are absolutely determined to plant something under that tree, going to our Recommended Species, click on Central Texas on the map, and then put in whatever characteristics, like light requirements, height, etc. that you want. Any plants you get on that search should be able to live in Central Texas. Whether they can survive that Live Oak trying to wipe them out is another question.

If you give up on that, how about a xeric bed of either decomposed granite, small gravel or shredded bark mulch under that tree? No watering, no fertilizing, no worries about sun or allelopathy.

 

 

 

 

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