En EspaŅol

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?

Share

Ask Mr. Smarty Plants

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

Search Smarty Plants
    
 
See a list of all Smarty Plants questions
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
Need help with plant identification, visit the plant identification page.
 
rate this answer
Not Yet Rated

Tuesday - June 19, 2007

From: Pflugerville, TX
Region: Southwest
Topic: Compost and Mulch, Propagation, Seeds and Seeding
Title: Allelopathc qualities in sunflowers
Answered by: Barbara Medford

QUESTION:

I have a sunflower patch in the corner of my backyard (Maximilians, common sunflower, and silverleaf sunflower)and would like to use the spent stalks (sans the seedheads) as mulch in the fall. However, I've read that sunflower is allelopathic to other plants. Is this only while they are actively growing, or would mulching with them inhibit growth of other plants? Are there certain plants that would or would not tolerate a sunflower-based mulch?

ANSWER:

Sunflower seed may be allelopathic in some situations, and certainly sunflowers will freely sprout everywhere, often with the help of birds, who are no doubt delighted that you are contributing to their diet. You should never use the seeds as mulch without first composting them for at least a month. The heat of the compost will help to leach out the toxins in the sunflower seeds. If you are going to mulch with stalks and leaves, removing the flowers and seeds, you would probably not need to compost first. Sunflowers grow so fast and so tall that they often will shade out weeds at their feet and/or kill them with the seed toxins. Most of the information I found on sunflower seeds damaging plants involved plants under bird feeders. The discarded seeds and hulls can build up to quite a depth if you are a devoted feeder of wildlife, and will certainly smother just about anything that tries to come up. In your case, you might just let the birds (finches are especially fond of sunflower seeds) enjoy the seeds still on the plants, then clean up the leftover debris and discard it NOT as mulch, at least until it has been composted.

 

From the Image Gallery


Maximilian sunflower
Helianthus maximiliani

Maximilian sunflower
Helianthus maximiliani

More Seeds and Seeding Questions

Problems with Eves necklacepods (Styphnolobium affine)
March 25, 2008 - Mr. S-P, I urgently need your advice regarding two Eve's necklacepods that appear to be dying. They are in two completely different areas of my yard. One began leafing out and then the leaves sh...
view the full question and answer

Seeding the banks of a large pond
October 18, 2011 - I have a 2 acre surface pond that is mostly a hard clay bank all around. The water level is way down and I will begin filling it very soon. I need to somehow being affordable, plant something or thing...
view the full question and answer

Native turf grass for Denison TX
January 27, 2014 - I have researched many grasses for sandy soil in Denison,Tx that are easy mantainance. Habiturf has been recommended but is mostly Buffalo grass and is not recommended for sandy soil. What other opt...
view the full question and answer

When to Collect Rudbeckia triloba Seed?
September 13, 2014 - How soon after flowering may I cut Rudbeckia triloba flower heads to save seeds? Do cones need to be attached to the plant in or out of the ground to continue to mature?
view the full question and answer

Inquiry about the Arizona Cypress trees in the Family Garden
March 20, 2015 - Dear Mr. Smarty Plants, I recently visited The Wildflower Center and enjoyed seeing several features that were new since my last visit two years ago. In the Family Garden areas I saw several beautifu...
view the full question and answer

Smarty Plants's Facebook profile Support the Wildflower Center by Donating Online or Becoming a Member today.

Mr. Smarty Plants wants you to be his Facebook friend. Click the Facebook icon to add yourself to Mr. Smarty Plants list of friends.
E-NEWSLETTER | BECOME A MEMBER | DONATE NOW | MEDIA | SITEMAP | STAFF
© 2015 Lady Bird Johnson Wildflower Center