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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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Saturday - March 30, 2013

From: Houma, LA
Region: Southeast
Topic: Invasive Plants, Non-Natives, Planting, Herbs/Forbs, Trees
Title: Planting petunias around base of oak tree from Houma LA
Answered by: Barbara Medford

QUESTION:

I live in south Louisiana and I want to plant petunias. Can I plant petunias around the base of an oak tree?

ANSWER:

There are 8 members of the genus Ruellia (wild petunia) native to North America, of which Ruellia caroliniensis (Carolina wild petunia) and Ruellia nudiflora (Violet ruellia) are native to in and near Terrebonne Parish in the southeastern portion of Louisiana. If you follow the plant links to our webpage on each plant you will learn that both like moist soil and can tolerate some shade. That would mean they could grow under an oak tree. BUT, you need to read this previous Mr. Smarty Plants answer about allelopathy in oaks and Ruellia brittoniana, which is the non-native Mexican petunia. Also see this Florida article about Ruellia or Mexican Petunia and note the warnings about its invasiveness.

Now, lets talk about the other petunia. Pelargonium (petunia) is a genus of 35 species of flowering plants of South American origin, closely related to tobacco, cape gooseberries, tomatoes, deadly nightshades, potatoes and chili peppers; in the family Solanaceae. From Google, here are pictures of the "other" petunia.

Frankly, we don't think either the native or non-native petunias would prosper under your oak tree, and the non-native members of the Solanaceae famly apparently need full sun, which we consider to be 6 hours or more of sun a day.

 

From the Image Gallery


Carolina wild petunia
Ruellia caroliniensis

Violet ruellia
Ruellia nudiflora

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