Hello,

I see a lot of lichen growing on the stems, and the green substance on your brick is lichen, too. They do not harm plants, they just grow on the surface. If they grow on brick, it indicates there is a high level of moisture present.

This article by Charlotte Glen / Pender County North Carolina extension agent, discusses when lichen can indicate a problem——

“Lichens do not harm the plants they grow upon, but often plants that are struggling will be covered in them. When lichens are found growing prolifically on a plant that also has lots of dead twigs and branches and that produces few, undersized or off color leaves, it is usually a sign that something more serious is going wrong. 

...If you have a tree or shrub that has recently been inhabited by lichen, which has been accompanied by loss of leaves and dying stems, there is a very good chance your plant is not healthy. In most cases, the plant’s problem is in its root system. Because roots are rarely seen it is easy to overlook how important they are to plant growth and health, when in fact the root system is the most important part of any tree or shrub. Roots provide plants with the water and nutrients they need to grow and survive. Just consider, a plant can loose all of its leaves and still recover, but if it looses all, or even most of its roots, it will die. 

One of the most common causes of root system problems is drowning due to water logged soils. Though roots live in the soil, they must have oxygen to live and grow. This is especially true for the tiny, sensitive roots known as root hairs. These fine roots are responsible for absorbing the vast majority of the water and nutrients plants need each day. Oxygen exists in soil in the tiny spaces between individual soil particles, but when these spaces fill with water there is no room left for oxygen, causing roots to literally suffocate. In addition, soils that stay wet often harbor root rot diseases that can slowly or rapidly kill susceptible plants.

There are no curative products available to treat or eradicate root rot diseases. The main strategy for dealing with these soil dwelling diseases is to plant trees and shrubs that are resistant to them. Which trees and shrubs to plant will depend on which type of root rot disease is living in your soil. 

Another case where low soil oxygen causes plants to grow poorly is in compacted soils. In these situations, where vehicle traffic or other factors have caused the soil to become hard and compressed, soil particles are pushed very close together, leaving little room for oxygen. Plants struggle in compacted soils because it is harder for their roots to penetrate through the soil, and low oxygen levels limit root growth. The only cure for compacted soil is deep cultivation and the addition of compost, which literally fluffs soils up, but this is only possible before trees and shrubs and planted. 

Once plants are in the ground, it is difficult to improve compacted soils without damaging plant roots, though mulching with pine straw or bark mulches will slowly improve the soil as the older layers of mulch decompose. In very compacted soils where plantings consistently struggle, the best answer is often to dig up existing plants, improve the soil, and replant. 

Roots can also be damaged during construction when they are cut by equipment digging in the soil or when heavy equipment compacts the soil they are growing in so severely they cannot survive. In these cases little can be done to remedy the situation. Whether or not a plant survives depends on how much damage was done and which species of plant it is, especially for trees since some can survive more damage than others. In all cases where root damage is causing plants to grow poorly, fertilizer will not help improve growth since damaged roots cannot take up nutrients very efficiently – the key to helping these plants grow better lies in finding out exactly what is going wrong and then fixing the underlying problem when possible. “

(End of article)

This is probably the issue with your shrubs. Over the years foot traffic, rain and snow pound and compact the soil. If a downspout or irrigation are present, the soil may be staying too wet. All can lead to root death or root rot. 

MSU Plant Diagnostic lab can confirm verticillium wilt for a fee. https://pestid.msu.edu

If verticillium is confirmed, you will need to plant a resistant species, such as a conifer, ferns, ornamental grasses, flowering quince, boxwood or holly.  Here is an article on verticillium showing a picture of a symptomatic branch and listing resistant species-

https://hort.extension.wisc.edu/articles/verticillium-wilt-of-trees-and-shrubs/

This list shows resistant plants, some of which are not hardy here but the list is extensive-http://depts.washington.edu/hortlib/resources/ucdavis_verticillium.pdf

Match the new plants to the soil type, pH, moisture and sun levels you have in the location. When choosing new plants, consider having a soil test done so you know what nutrients may be needed. https://homesoiltest.msu.edu

When planting, don’t break or injure roots or bark on main stems, remove burlap and twine or wire, and plant so the trunk flare is at ground level—-https://ag.umass.edu/landscape/fact-sheets/guidelines-for-planting-trees-shrubs

I hope this is helpful. Thanks for using our service.