Winter bud damage
Dormancy
In the fall, plant cells dehydrate and become inactive; this is what we call “dormancy”. Foliage and flowering buds which formed during the growing season will also stay quiet unless acted upon by an increase in temperature and humidity. Some species like apple and maple will respond quickly. Others like Gingko or privet are much slower and leaf out later in the spring.
Dormant bud in winter
The dreaded thaw freeze cycle
In late winter and early spring, the temperature may increase during a warm spell causing cells to gain water and swell. If followed by a sudden freeze, these will burst and die. We call this fluctuation a thaw and freeze cycle. Due to our location, NYC may have several every winter. Plants exposed to afternoon sun are at the highest risk or warming up and becoming damaged. Plants near exhausts ad other sources of heat are also susceptible.
Ice storms will also damage plants
Buds
Most plants have secondary buds on either side of the primary bud on the stem. These tend to be “asleep” and rarely ever develop into stems or flowers unless the primary one has died. If primary buds die from exposure, the plant begins a process of “awakening” the dormant ones. This may take several weeks, depending on the species.
A primary central bud with secondary accessory buds on its side
The secondary buds on some plants like privet come back strongly and very quickly leaf out. Others like maple may take an entire season to recover fully. Since these buds are also smaller, they may produce no flowers and many times have frail looking foliage.
Typical maple branch bud cluster - notice how tiny the secondary buds are !
What to do
The best response during the spring is to wait until the plant has finished producing all the stems and foliage the secondary buds are going to make. Then you can prune any dead tissue, papery or tan foliage, or dry brittle stems. Do not be excessive and prune off any branches that are leafed out - even if the overall shape of the plant is wonky!
At this point you can decide if the recovery was good enough and the plant looks pleasing in the garden - or if the time has come to toss it and get a new one.
Reducing the risk
Because the reality of rooftop gardening is all about planting trees and shrubs in a pot or container, roots may therefore be exposed to unaccustomed low temperatures. The soil in a container may even sometimes freeze solid. This may damage or kill root cells and the plant may not survive the winter. However, we have discovered that those that evolved to handle winters in zone 5 or lower are at the lowest risk for damage. Also the ones that are slow to wake up in spring.
A protected location may also help reduce these risks as would sometimes wrapping and covering plants and planters. That said, many times these options are not practical, feasible, or aesthetically pleasing.
Who wants to look at this all winter ! Ugly !!!
or this !!!!
By selecting alpine plants, you reduce the risk even more. Many needled evergreens as well as some groundcovers are the only ones that do well in the extreme cold. They also tend to wake up in spring after the risk of a spring freeze is over.
Conifers do fantastic in winter
So do hens and chicks !!!!
Deciduous trees like maple, and ornamental fruit trees like apple, cherry, plum, and pear - which we love for their amazing spring flowers ! - do not handle this freeze thaw cycle very well.
For the best plant selection - Call Plant Specialists TODAY !
Our Design or Garden Care Team can help you find tough hardy plants for your garden!
Don't delay – the sooner the better !
GREENING NEW YORK FOR OVER 51 YEARS !
Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBA
All photographs used with permission from @SHUTTERSTOCK