Strongbox inkberry holly yellow leaves problem #798395

Asked June 28, 2022, 7:56 PM EDT

What is causing leaves to turn yellow on my PW Strongbox inkberry hollies? I’ve been using 3-in-1 Bayer spray, thinking it’s a fungus.

Oakland County Michigan

Expert Response

There are a few possible causes for the yellowing leaves on your inkberry. 

The most likely cause may be your soil's pH level. Inkberry is susceptible to chlorosis (yellowing of the leaves) if planted in high pH alkaline soil. This is an acid-loving species that thrives in rich, consistently moist, acidic soils. If you haven't done so, you may wish to conduct a soil test to determine your soil's pH level. Self-mailer soil test kits from the Michigan State University Plant and Pest Diagnostic Lab are available. You can obtain them at the link below. Full instructions are there and also come with the kits. The cost is $25. The Lab will make recommendations for any needed soil amendments.

Another possible cause for yellowing leaves is improper planting. A common mistake gardeners make when planting is to set the crown, or the point where the branches meet the roots, too deeply in the soil. This can cause even a moisture-loving plant to suffer from oversaturation, as water is likely to pool instead of draining away,limiting the roots’ intake of essential oxygen. This is especially true if you have clay soil.

Inkberry can suffer from Root rots, Phytophthora and Thielaviopsis black root rot. They both cause yellowing of the
leaves, early leaf drop, slow growth and, eventually, branch dieback. Root rot occurs most often with flooding and extreme heat. Fungicides cannot cure the holly plant of this disease but can stop the spread. Thiophanate-methyl will help with Thielaviopsis root rot and etridiazole and metalaxyl with Phytophthora. As the diseases cannot be cured, prevention by planting the inkberry in well-draining soil is your best bet.

Check your holly bushes for cankers. Botryosphaeria canker affects weaker inkberry plants, usually following extremely high or low temperatures and drought. The canker causes similar symptoms to root rot, including yellowing of the leaves and
dieback. The cankers appear as sunken or cracked patches of wood, and girdle the stems so nutrients cannot reach the leaves. Prune out diseased branches as you notice them and take better care of the holly, watering during drought and mulching to retain soil moisture.

If you suspect canker or root rot, test the pH of your soil first as that is the most common cause of yellow leaves.

Finally, in Michigan the foliage may suffer from winter burn when temperatures drop below minus 15 degrees Fahrenheit, which can also cause yellowing leaves.

Here are some other cultural considerations for inkberry:

Inkberry has shallow roots, so it's good that you have added mulch around the roots. A 2-3" layer of mulch is a good idea. Inkberry holly thrives in a wet, cool climate. This distinguishes it from other hollies, which often prefer drier locations.

If you wish to trim or prune it, do so in mid-late spring, after the new growth has emerged.

Pruning should be done in late winter/early spring just before new growth emerges, but pruning needs are minimal unless you are using the shrubs in a hedge.

Inkberry prefers soil that stays moist. Avoid areas of standing water, but consider those places in the landscape that tend to dry out a bit moreslowly than others. Keep in mind that this shrub requires full sun to part shade.

Remove root suckers regularly if you don't want the shrubs to colonize and spread.

Fertilize in spring with a fertilizer such as Holly-Tone.

Strongbox is a female variety and will develop black berries if a compatible male pollinator is planted in the vicinity.

Sharon Globig Replied June 29, 2022, 1:19 PM EDT

I appreciate your answer. Great information. Adding some more background to my original question, I bought these (6) from a local garden store about 6-7 weeks ago. When purchased, they already had these yellow leaves, randomly throughout the plants, so they came that way from the grower. I went back to the garden store when things were not getting better, got advice from their “pharmacy center”. Followed the advice, the spraying, picking off the leaves and cleaning up debris from ground. At this point, I think I’ll dig them up and return them for a refund. I did order two from Nature Hills, NC, online bc I wanted 8 total. They arrived gorgeous. Full and healthy. I think I’ll order 6 more… Will I have to treat the soil the others were in? 

Lois Primeau Replied June 29, 2022, 3:57 PM EDT
It seems wise to return the two holly bushes with yellowing leaves for a refund. If they were potted, it could have been a root issue while in the pot. If you plan to order two additional bushes to replace those two, be sure to check the moisture content of your soil and well and its pH level in case it differs from the area where the bushes are thriving.

I see no need to treat the soil around the other six bushes if they are thriving.
Sharon Globig Replied June 29, 2022, 4:03 PM EDT

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