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Tuesday - April 21, 2009

From: Austin, TX
Region: Southwest
Topic: Planting, Herbs/Forbs
Title: Plants under oak trees
Answered by: Nina Hawkins

QUESTION:

I have a large live oak (actually several) in my front yard, which basically puts the beds at the foundation of my house in full shade. I tore out the builder-boxwoods and privets, hoping to plant something that would provide some interest. I'm having an awful time getting anything to grow there. Pigeonberries just died. Barbados cherries are spindly with yellowish leaves, beautybush just has 2 or 3 long branches sticking straight up, even the turk's caps look anemic. I've tried snapdragon vine and bleeding hearts and neither took hold. There are also some spindly roses in the bed that survive and flower occasionally. The soil is very rocky and I'm not sure what to do to amend it. Am I watering too much (doubtful) or too little? Should I just build up the edges of the bed and fill it with topsoil? I really want to xeriscape, because I don't want to have to spend every weekend babying my garden. HELP!

ANSWER:

It sounds like you have had these plants for less than a year, so my first piece of advice is to give them a bit more time.  When plants go into the ground, they are under a great deal of stress.  They are adjusting from a posh life at the nursery where they get a splash of water every day to keep their specialized soil slightly moist at all times to, in the case of a xeriscape, a life of scarce resources.  In some cases, it can take a year for a plant to really get established in its new home.  As if rocky soil and full shade weren't inhospitable enough, the roots of oak trees produce chemicals that retard the growth of other plants.  If the plants still don't take after temporarily babying them, you may want to consider putting down a thin layer of hardwood mulch instead and place your beds in a spot with more light.

All of the plants that you mentioned (aside from the rose, which requires full sun to be anything worth looking at) are part shade plants and while some part shade plants can survive in full shade, they can tend to get lanky in their search for light and this may be the case with your Malpighia glabra (wild crapemyrtle) (Barbados Cherry).  Rivina humilis (rougeplant) (Pigeonberry) is deciduous and may go dormant without extra water in summer.  Are you sure it's dead?  Callicarpa americana (American beautyberry) loses its leaves in the winter, so the "sticks standing straight up" are totally normal while the plant is dormant.  Mine are just starting to leaf out and hopefully yours will too.  Malvaviscus arboreus var. drummondii (wax mallow) (Turk's cap) will freeze back in winter and you can cut it back when this happens if you like.  Like most plants that tolerate shade, these plants prefer to live in moist soil and are competing with your trees for water.  We recommend adding a couple inches of hardwood mulch or compost to your bed each year so that you can build up the soil slowly and not have to worry about smothering tree roots.  Below are links to the information pages of two other plants for shade that you may want to try:

 

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