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
7 ratings

Tuesday - May 06, 2008

From: Georgetown, TX
Region: Southwest
Topic: Compost and Mulch, Diseases and Disorders, Watering, Herbs/Forbs
Title: Yellowing leaves
Answered by: Barbara Medford

QUESTION:

What causes yellowing of native garden plant leaves?

ANSWER:

You may be overwatering them. On the other hand, you may be underwatering them. Isn't that wonderful? Some of the causes are environmental, as this information from a website by Suite 101 indicates.

Too much water in the soil will prevent oxygen from getting to the plant’s roots, thereby smothering them. As roots die, the foliage above ground starts to discolor and die. Overwatering also promotes fungal root diseases such as armillaria and phytophthora.

Under watering will cause leaves to wilt, fade in color to a dull shade, and drop prematurely. The new growth at the tips of the plant may wilt in the afternoon and then recover in the evening. If the plant is under prolonged stress from lack of water, new leaves will be smaller and the plant will become increasingly susceptible to insects and disease.

If a plant is lacking in iron, new foliage will be small and it will fade to a yellowish green, starting at the edges of the leaf and spreading inward until only the veins remain green. If the plant is lacking nitrogen, older leaves will uniformly turn yellow.

To correct iron-deficient soil, aerate the soil around the roots and spread an iron chelate evenly over the soil beneath the plant canopy or apply it to the foliage, according to the product label. If you regularly mulch with composted organic matter, you will eventually remedy the iron deficiency.

A nitrogen deficiency can be fixed quickly by applying a nitrate fertilizer but this will tend to promote more rapid, succulent growth, which attracts aphids and mites. An organic form of nitrogen, such as compost, which must decompose before being absorbed by plants, will prevent the excessive growth.

Another reason may be where you are in the growing season. If leaves are through growing, they will begin to turn yellow, and be replaced by fresh, new green leaves. At the end of the growing season, the whole plant may begin to yellow.

So, we really haven't helped you much, have we? If a lot of your plants have a lot of yellow leaves, we'd say you had a drainage problem. Either the water is going into soil, like sandy soil, that drains too fast, and leaves the plants dry, or into clay soil, where it stands and begins to suffocate the roots. We would suggest going the aerating and composting route suggested above, because that will really fix all the problems. If just a few leaves here and there are yellow, it's probably not a big concern, but the organic mulch is still a good idea. It's something that is good to do on all your plants, over time, and makes them healthier.

 

 

 

More Herbs/Forbs Questions

Failure to bloom of coreopsis
July 16, 2008 - Hi, 2 things..asked a question last yr re: scuttelaria (sp)-purple etc..you could not locate. Finally did at High Country Gardens in NM. Now a new question: Cannot get my coreopsis to bloom.. Have di...
view the full question and answer

Gaura Plants Dying In PA
July 16, 2014 - I had six gaura plants. They were beautiful last year. Now I have one that is doing well and the others are dying slowly one at a time. I don't understand this. They are on a slight slope and have ...
view the full question and answer

Sharing Selfheal with Texas Friends
April 25, 2013 - I have discovered selfheal plants in my yard. When and how do I collect the seeds or do I just dig up plants to share with friends? I understand this is actually an herb. I love identifying wildflower...
view the full question and answer

Native plants for southwest exposure in Tulsa OK
April 24, 2008 - I want to plant something in a bed on the South side of my house with some Western exposure. The space is in a bed that would share space with a Red Tip Photinia (next to the house)& liriope( on the ...
view the full question and answer

Gaura drying out in Plano TX
May 13, 2012 - My gaura plant of 3 years suddenly seems to be drying out and no longer green or blooming?
view the full question and answer

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