Yellow patches on many perennial garden species

Asked May 18, 2017, 9:09 PM EDT

This spring I noticed yellow spots/patches on many of my perennials in one of my gardens. Most of the plants have been in this garden, which surrounds a very large brick patio for 2-3 years. My soil is *very* sandy and I do not amend or fertilize (I want low maintenance gardens, if it doesn't do well, I'll try something different). We did put down about an inch of uncolored mulch last spring, but it wasn't enough and we'll be adding more this year. I noticed the yellowing first on a grape vine. Some of the grape leaves are like the picture, some are more patchy. I then realized that many of my other plants showed similar symptoms: anise hyssop (pictured), penstamon (pictured), phlox, wild violets, salvia, hydrangea, and more. Other than the discoloration, the plants look great and are all growing well. I'm most concerned if this is some sort of widespread infection, though I was also wondering about chlorosis (but why didn't it happen in the past or elsewhere in my yard?). Thank you so much!!!

Anoka County Minnesota

1 Response

Thank you for the question. When such a wide variety of different plants are afflicted with the same symptoms at the same time, we usually consider factors other than infectious disease or insect pests. We think of things like soil issues or possibly herbicide drift injury.
Some types of herbicides applied elsewhere can drift in on the wind and affect non target plants with a bleaching effect. Often, the plants aren't seriously injured and recover shortly. There isn't much you can do unless you know who sprays what. If you know, you can talk with them, figure out what the chemical is, and develop a strategy so that it doesn't happen again. Spraying when there is little to no wind will often solve the problem.
Chlorosis is another likely problem. Our colleagues at University of Illinois Extension explain chlorosis like this:
" Chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots, high alkalinity, and nutrient deficiencies in the plant. Nutrient deficiencies may occur because there is an insufficient amount in the soil or because the nutrients are unavailable due to a high pH (alkaline soil). Or the nutrients may not be absorbed due to injured roots or poor root growth".
Since you have sandy soil not fertilized or amended in any way and the plants are growing by a large patio, the problem could be lack of nutrients and high pH. We suggest you get a soil test to determine pH and any deficiencies. Plants can be low maintenance if soil conditions are correct and they are well established. You might have to roll up your sleeves and amend your soil according to soil test results. If your soil pH is above 7, soil nutrients are less available to the plant and nutrient deficiencies can result that look a lot like what I see in your photos and you will have to correct the problem for the future success of your plants The soil test will instruct you on how to correct any imbalances.
As for your question why did this problem show up this year and in this location? It's hard to say. Herbicide injury is random. If chlorosis is your problem it could originate with your very large patio because lime can leach out of cement and grout causing a raise in soil pH. Nitrogen is crucial to normal plant growth but is highly mobile in soil, especially sandy soils. You can't go wrong by working in a good nitrogen source like compost and adding a slow release fertilizer.
How to submit a soil test: http://soiltest.cfans.umn.edu/

Thank you for contacting Extension.