How To Prune Grapevines – Four Arm Kniffin System

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A step by step tutorial on how to prune grape vines using the four arm kniffin system of pruning and trellising.

What is the four arm kniffin pruning system?

In this tutorial, we will show you how to prune grapevines using the four arm kniffin system. The four arm kniffin pruning system is a very simple grape pruning process that allows plenty of light to get to the plant in the summer while also protecting it in the winter.  It consists of a lower trellis wire about 3’ off the ground and a higher trellis wire about 5-6’ off the ground.  Each wire supports two lateral canes, two on the bottom and two on the top which come off of the main trunk.  The wires are supported by posts in between each grapevine that are kept tight by a turnbuckle supported by a post at each end of the trellis.  When we planted our grapes, we planted them 10 feet apart and then put one support post for the trellis between each grapevine.    

What type of grape grows well on the four arm kniffin trellis system?

The four arm kniffin system of pruning and trellising works well for labrusca or concord-type grapes which are the kinds of grapes that tend to grow best in northern climates.  The four kinds of grapes we planted are somerset, mars, marquette, and a concord grape that grows wild in Nebraska.

Seedless Eating Grapes

Somerset is our favorite seedless grape for fresh eating.  We ordered ours from Jung Seed.   “Wisconsin bred, northern hardy. The earliest, sweetest, hardiest and highest quality red seedless grape available. Bred by Elmer Swenson, a pioneer of grape breeding from Osceola, Wisconsin, this table grape bears clusters of medium sized, seedless berries with sweet strawberry-like flavor. While edible at the pink stage in August, flavor will be even sweeter if left to ripen to full red. Superb for fresh eating, juice and jelly. Quite disease resistant.”

Mars Seedless Grape is our purple, seedless, eating grape of choice.  It also makes great juice and jelly.   “Among the hardiest of the seedless dark blue grapes, ripening in late August to early September. Fruits are slipskin, medium to large, sweet and juicy with flavor similar to Concord. Delicious fresh and superb for jams, jellies, wine and juice. Vigorous vines are productive and dependable with good disease and mildew resistance.”

Seeded Juice Grapes

Marquette is our top producing juice grape and is also great for jelly.  “Hardy and highly disease resistant with excellent wine quality. This University of Minnesota release has superb wine-grape parentage that includes Frontenac and Pinot noir. The berries have a high sugar content and moderate acidity, producing wines with ruby-red color and a bouquet with notes of cherry, berry, black pepper and spice. Resists Downy Mildew, Powdery Mildew and Black Rot. Plants have an open, orderly growth habit. Ripens mid-September.”  

Our concord variety was planted from cuttings off of the wild concord grapes that grow here in Nebraska.  Concord grapes make the best juice.  They are very hardy and easy to grow, I would highly recommend growing them.

When should I prune grapevines?

Grapevines should be pruned during their dormant season in the late winter.  The best time to prune them is anytime after the new year and before they bud out in late March or early April.  In Nebraska, we usually get a warm spell called our “January thaw” sometime in the month of January, and I always try to get outside and enjoy the sunshine and warm weather while pruning the grapes.  Dormant pruning is a job I enjoy every winter.

What happens if you don’t prune grapevines?

Grapes will produce fruit during the coming season on one-year-old wood that grew during the previous year.  Any wood that is older than one year will no longer produce fruit.  If that older wood is not pruned out, the new growth that grows the following year will keep growing off of the old wood and over time get farther and farther away from the main trunk.  This weakens the vine over all which lowers fruit production and makes the grapes harder to pick.  It’s necessary to do regular pruning on your grapevines to maintain good fruit production.

Training system for young vines

If proper pruning methods are followed from the beginning, you will have a strong mature grapevine that will produce grapes for many years to come.  Grapes can be ordered bareroot from many seed catalogs, or purchased as potted up starts from a nursery.  We ordered ours bare-root, and just dug a small hole in the ground and planted them in early spring.  Be sure to plant them with plenty of spacing, because when they get to be full size they take up a lot of room and tend to grow into one another.  We planted our vines 10’ apart and have been very happy with the results.  I recommend setting up your trellis soon after planting your grapevines.  

The first year…

For the first growing season, you will need to put a stake beside each plant for them to crawl up until they can reach the first trellis wire.  This will help them to grow straight and keep them supported.  Sometimes several shoots will be growing from the base, but it’s important to choose one main stem and prune back the rest. This will ensure that all the energy from the plant goes into growing a strong main trunk.  

After the first year of growth, the grape should reach at least the first wire, and maybe even the second wire. If the top of the vine above the first wire is very small and spindly, you can cut it back to just above the second wire.  This may seem counterproductive, but it will encourage stronger growth for the following season.  The goal is to have two lateral shoots coming off the main trunk on each wire, and cutting the vine back near the first wire will encourage it to branch out at that point.  

The second year…

The following year it will continue to grow up towards the second support wire as well as laterally in opposite directions along the first support wire.  I recommend using trellis support clips to attach the vine to the wire as it grows.  Once it reaches the top wire, you can choose strong side shoots to grow laterally on the top wire just like they do on the bottom wire.  I usually do some light cane pruning and training on the plants during the summer if needed to encourage next year’s fruiting canes to grow in the right direction.  After a couple of years of growing, you should have your main trunk established and some lateral fruiting vines attached to the wires.  

How to prune mature grapevines

Once the vines are mature and start producing fruit, you will want to prune out all the two-year-old wood back to the main trunk.  The two-year-old dormant canes will be a light gray color with peeling bark.  Typically there will be several shoots of one-year-old fruiting wood coming out from the trunk in each direction on each support wire. The one-year-old growth will be a chocolate brown color.  These are the canes that will produce fruit in the coming year.

Choose the strongest one of each of the fruiting vines, one going in each direction on each support wire, to leave for the upcoming season.  If these fruiting vines are exceptionally long and spindly at the ends, you can prune them back until the wood is about the size of your little finger.  The stronger the wood, the better it will be able to support fruit. The recommended number of buds on the new fruiting canes is at least 8 to 10.  The rest of the fruiting vine can be pruned back flush with the main trunk except for where you want renewal spurs for the new growth the following year.  It can be tempting to keep more of these one-year-old canes, but doing so will result in smaller fruit.  After pruning, you will want to remove all the old canes you have trimmed out to reduce fungal diseases.

Renewal Spur Pruning

When learning how to prune grapevines, it is important to understand how to get new growth for the coming year. Renewal spurs are attached to the main trunk, and this is where the new canes will grow this coming year that will produce fruit clusters the following year.  You will want to leave a renewal spur as close to the main vine as possible. One pointing in each direction on each support wire.  You will only prune these back to the first node or bud along the cane, usually about 3-4” from the main trunk.  Once cut here these will branch out from there and grow new shoots for the coming year.  Because I live in zone 4, I sometimes leave an extra renewal spur if there’s more than one, in case of winter damage.  

Growing grapes in northern climates

The last couple of winters have been extremely cold, even dipping to -60 windchill a couple of times. Our grapes have survived these winters with no problem.  The biggest challenge with growing grapes in a northern climate is late frost in the spring.  If you only have a few grapes, you can cover them if they are in bloom when the frost comes.  If it’s only a light frost (31 degrees or above), I have had success with turning sprinklers on before the sun comes up and letting them run until well after sunrise.  This puts ground temperature water (54 degrees) on the leaves and blooms and keeps them at that temperature until the danger of frost is past.  

Our success with this pruning system

We planted our grapes in 2018 and have been extremely happy with this pruning system.  It is easy to keep up with the pruning and makes harvesting a breeze.  We canned over 100 quarts of grape juice concentrate last year which we use for grape juice and jelly. We also enjoyed lots of grapes for fresh eating.  Grapes are relatively easy to grow and a fun and useful addition to any homestead.  Please comment below with any questions you have about growing grapes and how to prune grapevines in a northern climate.

Watch our full tutorial on how to care for grapevines over on YouTube

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