Rent Shop Volunteer Join

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

Please forgive us, but Mr. Smarty Plants has been overwhelmed by a flood of mail and must take a break for awhile to catch up. We hope to be accepting new questions again soon. Thank you!

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

Difference in acorn yields from Georgetown TX
December 27, 2012 - Why do some live oaks produce acorns in abundance and others do not?
view the full question and answer

Blackfoot Daisy care in Marble Falls TX
February 21, 2016 - I've planted and killed a number of blackfoot daisy plants. I know it's a hardy plant that, once established needs little or no care. But what about getting them started? What care do they need f...
view the full question and answer

Wildflowers for floodplain near Denton, TX
March 22, 2015 - Hello, I am a member of my HOA board and am researching the possibility of filling in our floodplains with wildflowers. Currently the floodplains are grass only and span a few acres. Our goal is to t...
view the full question and answer

When is the best time to plant or seed after a wildfire?
April 29, 2009 - This past week our 1 acre lake property at Possum Kingdom Lake in north Texas was scorched by a wildfire. No brush, grass or bushes remain, and we're hoping not to lose all the cedar and mesquite tr...
view the full question and answer

Planting bluebonnets
April 20, 2008 - How long do bluebonnet seeds take to mature, and when is the earliest in their development they can be harvested? When can they be scattered?
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.