inkberry turning yellow

Asked September 28, 2020, 4:48 PM EDT

I have a hedge of thirty inkberry bushes in my yard. They are over 2 years old. Suddenly I've noticed the lower, inside leaves on all 30 are turning yellow, orange and red. The outside and top leaves remain green. The area soil is sometimes soggy but now is just damp. Would love to find out if this is normal or a disease.

Worcester County Maryland

1 Response

This leaf color change could be due to normal leaf shed or to root health issues - the symptoms can be essentially identical between the two. Inkberry Holly naturally becomes a bit leggy (bare-bottomed) with age, though this process will accelerate on plants not grown in full sun (6+ hours daily in summer). When leaves are shed, it is the older ones - lower and interior on the branches - that go first. Color change is common among shedding leaves because, like trees in autumn, the chlorophyll production is halted as the leaf prepares to drop, which allows other leaf pigments to be seen before they fully dry out.

When roots are unhealthy, they will struggle to supply the top of the plant (branches, leaves) with enough moisture and nutrients to keep them healthy and alive. Sometimes, this results in leaf sunburn or branch dieback, but in some cases, this results in premature leaf drop. As before, old leaves are sacrificed first since they have contributed to the plant's growth the longest and were going to be shed sooner or later anyway; losing them has the least immediate impact on the plant's ability to photosynthesize to feed itself. Sometimes, roots which are rotting in overly-wet conditions (because they don't have enough oxygen), the ethylene gas they produce in the process triggers leaf drop - the roots closest to the ground get the biggest does of gas and shed in response.

Inkberry is quite adaptable to wet soils overall, but the commonly-used cultivars may have less tolerance for it than their wild relatives, which can be seen growing in shallow standing water in some places. That, or some condition present in the wild that prevents rot there is missing in our gardens. In either case, make sure these plants are both getting the water they need during dry periods but also not being over-watered; always feel the soil moisture before watering to make sure it's needed. Checking about five inches down is a good measure; if moist, they can probably be left alone; if fairly dry, soak the root area well. It sounds like this site tends to stay wet rather than dry out, so it's possible they're stressed from being too damp for too long of a stretch. There is nothing you can do about this except to give them time to recover, change the drainage leading to that spot (if possible), or build them a raised bed and re-plant into that (probably not practical given how many shrubs you have). No fungicide is going to be practical or even effective if root rot is occurring.

The encouraging sign is that it appears no branches are dying outright and new growth appears normal, at least where we can see it. This implies the roots are not too badly damaged and recovery is possible. Symptoms can often be slow to develop on evergreens, though, so if decline accelerates in the future, the initial cause occurred awhile ago and nothing can be done except to replace any failing plants.

It looks like landscape fabric is used underneath the mulch here. If so, it may be contributing to the problem by hampering oxygen exchange with the soil and inhibiting evaporation of excess moisture, even though landscape fabric has fine holes made for water movement. If possible, it would be safest to remove it entirely and rely just on mulch to suppress weeds and control erosion.