Research at several agricultural experiment stations throughout the country has shown that trees and shrubs should not be heavily pruned or fertilized at this time of year. Wait until late October or early November, or it can be done in late winter or early spring.
If the pruning or fertilizing is done now it might stimulate new growth which would not have time to harden (acclimate) for winter and could result in serious injury to or death of the plant.
Many gardeners fertilize their roses in order to get a bigger and better display of flowers. According to specialists, a moderate application will do no harm, but more than that may be risky. A moderate application would be a heaping tablespoonful of 106-4 for each plant.
As days get shorter and the weather cooler in late summer and early fall, plants start to acclimate (adjust) for winter.
A plant is hardy only when it has hardened. If cold weather comes before it has acclimated, the plant may be seriously damaged.
The degree of cold weather the plant can survive after it has hardened depends on its heritage. With pyracantha coccinea "Lalandii," for example, the stems and leaves can survive minus-15 degrees Farenheit when fully acclimated, but would be killed by a few degrees below freezing if unprepared.
The roots of the plant are much less hardy than the top of the plant, and mature roots are much more hardy than young ones. With pyracantha, for example, the killing point is about 2 degrees for mature roots and about 24 degrees for young ones.
However, the low hardiness of the root system usually is not a problem with field-grown plants because soil temperatures do not get low enough to cause injury. It is different with plants growing in containers. The containers and consequently the root systems are above ground, surrounded by the cold, circulating air rather than the relatively warm, insulating environment of the soil. For example, the roots of plants in containers can be exposed to temperatures of 5 degrees at the same time the roots of field-grown plants three inches below the surface are only about 21 degrees.
The first winter is often the hardest for newly-planted trees and shrubs.