Pruning: cold Climate Wine Grapes
Date: January, 2021
Madeline Kay Wimmer, M.S.
Knowing where, how, and what structures to prune can initially seem confusing for new grape growers. By learning vine anatomy and where the fruiting zone occurs on a grapevine, as well as following proper pruning techniques and tools, the art and science of pruning becomes less calculated and more natural.
Sections
Grapevine Life Cycle
Gross Vine Anatomy
What is a Node?
Grapevine Node and Compound Bud Anatomy
When to Prune
Pruning Diagrams
What to Prune
Cane Selection: Strategy and Techniques
Envisioning a Healthier and Sustainable Yield
Vine Balance
Tools
Grapevine Life Cycle
Grapes are botanically classified as woody vines, or lianas.
During the first year of growth, shoots from the grapevine grow without end (indeterminately) until cold weather triggers dormancy within the plant, causing the shoots to become woody.
The following growing season, new shoots break from nodes located along the one-year-old shoots (i.e., canes).
Year after year, shoots will continue to break from new canes, while older parts of the vine (e.g., trunk and cordon) continue to age and grow in terms of girth, similar to they way trees and other woody perennial plants grow.
Gross vine Anatomy
Cane– a shoot that has matured after one growing season. Fruit set occurs on shoots originating from buds located along the canes.
Cluster zone– region of the vine where fruit clusters develop.
Cordon– two years and older, the “arms” of the vine that give structural support to the cluster zone.
Spur– a cane that has been pruned to 2-4 buds tall depending on training system. Bud/shoots that originate from the spur bear fruit.
Trunk– provides the main structural support for the grapevine canopy. The trunk is trained first during establishment and is usually the oldest perennial structure on a grapevine.
Watersprout– a shoot that arises from the trunk, cordon, or other older woody parts of the vine.
Sucker– a watersprout that arises from below ground.
What is a Node?
Defitinition: Nodes are regions along the shoot where leaf attachment occurs.
In addition to a leaf, each node also contains a lateral shoot, tendril, and a developing bud that will produce shoot(s) the following growing season.
Grapevine node- where leaf (L), compound bud (B), lateral shoot (Lat), and tendril (T) originate.
Illustration by Madeline Kay Wimmer, M.S.
Node Anatomy
Compound Bud– develops during the current growing season, which will be the growth source for shoots the following year.
Lateral shoot– a shoot that branches from the side of another actively growing shoot.
Internode– the region between each node.
Tendril– a twine-like, modified leaf that grow opposite to each leaf at the node region, and is provides structural support for the plant.
Compound bud showing the primary (P), secondary (S), and tertiary (T) buds.
Illustration by Madeline Kay Wimmer, M.S.
Compound Bud Anatomy
Primary bud/shoot– within a compound bud, the primary shoot is the first shoot to emerge and is often the largest and most fruitful shoot.
Secondary bud/shoot–the secondary shoot can also produce fruit, but usually is less fruitful that the primary shoot and only breaks if the primary bud/shoot is dead.
Tertiary bud/shoot–the tertiary shoot is the final shoot to grow if both the primary and secondary shoot dies. It usually only produces vegetation to maintain the grapevine’s heath.
When to prune
Prune grapevines after they have gone completely dormant and after the risk of extreme cold winter temperatures has passed.
For many moderately cold climate regions, this means pruning sometime after the beginning of February, but it can be delayed until mid-march or later for very cold regions (Zones 4b and colder).
If necessary, vines can be pruned post-budbreak, but take caution during this time to prevent breaking off enlarged buds and newly emerged shoot tips.
Pruning diagrams
Before Pruning
Shoots removed during pruning
After Pruning
What to Prune
The goal of dormant pruning is to reduce the vine’s total node/bud count. When pruning is neglected, all viable buds will start to grow along each shoot, transforming its structure from a trained vine into a bush. A grapevine bush looks great and shades well growing on a pergola or some other structure, but is counterproductive for fruit production.
Note: The diagram on right shows an example of a grapevine cordon (High Wire Cordon) from above. Red marks show suggested pruning cuts to make that ultimately select a single cane to become next season’s spur. The old spur in this image will be cut and removed, taking out the other excess canes within the region, to create fist sized spacing between each spur on the cordon.
Fruit Set Occurs on shoots originating from Compound buds located on Canes (One-year-old wood)
Latent buds located on the trunk(s), cordons, older spurs, or other older, woody regions will also produce shoots, but they are usually only vegetative, rarely setting fruit.
Training Systems
Unwanted canes are removed during pruning while the remaining canes are pruned to 2-3 bud spurs for upward training systems (e.g., Vertical Shoot Positioning) and 3-4 bud spurs for downward systems (e.g., High Wire Cordon).
Technique
Cane pruning
When pruning canes into spurs, cut about 1/2 inch above the top bud at an angle to mitigate cold damage and prevent water from pooling on the spur tip.
Cleaning up old/damaged wood
Additionally, remove any old tendrils or excess wood that may be accumulating on or near spurs, along the cordon. Older wood, such as a 2+ year old spur that are no longer functioning, or a damaged cordon, should be cut as close to the vine and as “clean” as possible to prevent pathogens and small insect pests from building up in unviable wood. (More information about restorative pruning to be discussed on a different page.)
Cane Selection:
Strategy and Techniques
Cane Health
Create healthy spurs by selecting canes with healthy, living buds and stem tissue.
Healthy canes tend to be round, pencil sized in diameter, produce nodes every 3–4 inches, and range from tan to brown in color.
Color
Lighter tan to white colored canes can be a sign of cold damage (some cultivars do have a lighter cane color). Damaged canes have buds and stems that are brown and dry inside, whereas healthy canes generally have green living tissues within.
Vigor and size
Weak, thin, spindly canes are less productive, easily damaged by cold winter temperatures, and make poor spurs. Additionally, overly vigorous shoots (i.e., bull canes) can result from high fertility sites, should also be avoided for selection. Bull canes are characterized as having oblong and sharpie marker width or larger sized diameters, and nodes spaced at 5+ inches a part. It may feel intuitive to presume that bigger shoots are healthier, however bull canes tend to be less productive and cold hardy than healthy, medium sized canes.
Cane Position and Spacing
Creeping Spur: Selecting the highest positioned cane, year after year, causes “creeping spurs” as seen below (a). It can be renewed by pruning off the old spur (a) and replacing it by one of the canes (b) on the right or left.
Position
Canes/spurs should be positioned in the direction suited to the given training system. A downward training system, for example, ideally has all its spurs positioned downward. Pay attention to bud direction on spurs, too, which will directly determine the direction in which the shoot will grow during that season.
Spacing
Avoid situations such as leaving two spurs next to each other with buds that will eventually cross over within the canopy, causing a disorderly canopy. Aim to select canes located closest to the cordon to prevent spurs from becoming too tall, which eventually reduces canopy space for shoot growth and presents problems for future spur replacement.
Note
Keep in mind that most grapevines will not have the ideal pruning situation with perfect cane health and alignment.
Work with what is available and learn from mistakes. Even an extreme mistake, such as accidentally removing a desirable cane, which can be corrected within years.
Envisioning a Healthy and Sustainable Yield…
Yield can be somewhat estimated based on the number of nodes/buds retained per vine. Because most grape cultivars set two to three clusters per shoot, growers can multiply the number of retained nodes/buds by clusters set and roughly(!) get an idea of that seasons yield by cluster number.
Vine Balance…
Grapevines have a limited amount of sugar reserves and nutrients to put toward fruit, vegetation, roots and woody tissues of the vine each growing season. Therefore, it is important to consider how much fruit a grapevine can set before it is overcropped, which is variable and influenced by vine health, age, and genetics. Vine balance is often estimated by comparing fruit yield to the amount of wood produced/prune off each season.
Growers can calculate values based off of these ratios, however, the most important idea is to simply observe if a lot of wood weight, a medium amount, or a light amount of poorly developed canes were left by pruning time. Vines with a lot of pruning wood can be cropped heavier, vines with lighter canopies should be cropped less.
Basic Hand Tools
There are many different hand tools available to assist in pruning. Basic pruners are generally used to cut back canes, while loppers are best used for spur and cordon removal or replacement. Handsaws can occasionally be helpfully if trunk removal is necessary.
Semi-mechanized Hand Tools
Ratchet pruners and loppers, pneumatic pruners, and electric pruners can speed up the pruning process, but still require “hand” labor. Such tools are an appropriate option to increase efficiency and prevent injury from the repetitive motions of pruning.
Mechanization
Additional mechanization options also exist that utilize tractor equipment. If mechanization is desirable, be sure that the chosen method and equipment is compatible with the training system and trellis structure.
Summary
Learning grapevine anatomy, where the fruit zone occurs, and when to prune is key to pruning success.
Canes are pruned back annually to create new spurs where the fruiting shoots will emerge.
In addition to cane pruning, growers may have to remove spurs and even damaged cordons and trunks, if necessary.
Cane selection is based on color, diameter size and shape, position relative to the fruiting zone, angle, spacing and overall health appearance.
Grapevine pruning tools can be classified into three categories: hand tools, semi-mechanized hand tools, and fully mechanized. Tools change cost efficiency, worker ergonomics and comfort, as well as overall pruning time.