In the vineyard
Grapes are easy to grow and can provide fruit all summer long if you have multiple cultivars (varieties) whose grapes ripen at different times. What you do in the winter and spring months lays the groundwork for healthy grapevines with a good fruit crop.
Grapes - Basic vocabulary
- Arm - an old spur that has become woody and fat over time, usually extending upward from a cordon
- Bud - located at a node on the cane, it produces either a shoot, tendril, leaf or cluster
- Cane - a mature, woody shoot
- Cordon - a permanent branch of a vine trained to grow along a wire or on an arbor
- Cultivar - a plant variety that has been produced in cultivation by selective breeding
- Head - the area of a cane-pruned vine from which arms and fruiting canes emerge
- Internode - the portion of a shoot or cane between two nodes
- Node - the point on a shoot or cane where buds emerge and form clusters, tendrils, leaves and lateral shoots
- Shoot - a young cane that has not hardened. Typically a shoot becomes a cane by the time it enters dormancy in the late fall
- Spur - a cane pruned to four or fewer buds
- Tendril - a twining and clinging organ used for support
- Trunk - main stem or body of the vine between the roots and the head or cordons
Grapevines are dormant in January and the weather is wet—not a good time to prune. From late fall through early February, rain and wind carry microbes that can enter grapevines through pruning cuts and eventually kill the vines. However, January is a great time for planning. Since all the leaves are off the vines it is easy to see plant structure, making this month the best time to select and mark wood for cutting or keeping when you prune in late February or early March.
The answer lies, in part, in where the fruiting zone is on each cultivar. Here is a picture of a grapevine shoot. Each point at which a leaf, cluster or tendril appears is called a node. Mature, woody shoots are called canes. Canes have visible and invisible buds that formed last year at most nodes. These buds will sprout shoots, some of which will have grape clusters this year.
Cultivars differ in terms of where the fruitful buds are. Some cultivars (e.g., Red Flame, Italia, Tokay, Merlot) have their fruitful buds lower on the cane, close to the trunk and/or cordons, on nodes 1, 2 and 3. Other cultivars (e.g., Thompson Seedless, Concord, Suffolk Red) have fruitful buds on nodes 4, 5, 6 and beyond. And a few cultivars (e.g., Summer Royal, Diamond Muscat) have fruitful buds all along the cane.
To accommodate this difference in cultivars, viticulturists have come up with two basic pruning styles (more on both in the February section of this checklist):
- spur pruning, where all fruiting canes are drastically shortened, and
- cane pruning, where fruiting canes are left long.
Have you ever pruned a vine only to get no clusters at all that year? You may have spur pruned a cultivar that needs cane pruning. On a Thompson Seedless, for example, if you cut all the canes short, you have cut off all your fruiting buds!
Here is a good video of Chuck Ingels, former UC Cooperative Extension Farm Advisor for Sacramento County, explaining the difference between the two basic pruning styles.
If you don’t know whether your cultivar should be cane or spur pruned, you can google the cultivar name. If you don’t know the name, cane prune it, then watch to see where the clusters develop. If they develop on shoots that grew close to the trunk, you may spur prune it the next year. But if they grow farther out on the canes, then continue to cane prune.
When you examine your cane-pruned vines, look for healthy canes to keep as long, fruiting canes. A healthy cane is around the size of a pencil up to ½ inch thick, at least 10-12 nodes long, free of cracks or breaks, and round. Ideally the cane is headed in the desired direction so that you can tie it to your supports. Canes that are up high in the canopy probably got a lot of sun last year and are often cinnamon in color. They will be more fruitful than canes that were shaded or headed downwards. If possible, avoid any canes with a lot of dark scarring as shown below. The scarring indicates that the vine was infected with powdery mildew last year.
Tag healthy “keeper” canes with colored stretch vinyl ribbon to remind yourself not to prune them off later. Generally, you will select between two and eight canes on the vine to keep long. The final number depends on your available space as well as the vine's age and health. On very young vines, you might just keep one cane on each side of the vine. Don’t make any cuts at this point, just tag the vines. Get help on how to tie vines (PDF) and what kinds of ties to use.
With grapes, you are always thinking about two crops at once: this year’s, and next year’s. For each long cane you keep, you also want to create a renewal spur. Renewal spurs will produce shoots which turn into next year’s canes. To make a renewal spur, select a cane that's high in the canopy and as close as possible to the main trunk. Mark it with a different-colored tape. Renewal spurs are cut back to two to three buds. It is good to preserve an extra renewal spur as insurance.
On spur-pruned vines, look at the spacing. Arms should be spaced about 6 inches apart.
- Are there areas where arms are too close together?
- Are there arms or potential spurs that appear to be damaged or dead?
Your goal is to have one spur on every arm, and every spur will have two to three buds.
- Are there arms with too many potential spurs?
Mark unwanted arms with a different color of vinyl tape for removal in May or June, when the weather is warm and dry and the plant can more easily heal a large cut. In late February or early March you will come back and cut canes to spurs with two buds each.
Other January tasks:
If you have not done so recently and you are using drip irrigation for your vines, check for leaks, and flush your system. You will need to water newly planted vines, but there is no need to water established vines in the winter months, except in a drought. Here is a comprehensive guide for maintenance of micro-irrigation systems.
Look for trellising needs. Order supplies: sprays, netting, rubber ties or vinyl ribbons for trying the shoots to the supports.
Clean and sharpen pruning tools. Here is a good article on why it is important to sterilize your pruning tools (PDF).
January is a suitable month to plant new vines if the ground has not frozen and is not too wet. You should be able to find bare root grape plants in nurseries, or you can order them online. You can also order cuttings and propagate them at this time. Order from a reputable grower. One excellent local source for cuttings is the Foundation Plant Services at UC Davis. They have links to other certified growers in California.
Here are links with basic information about the care of young vines:
Grapevines need to be pruned each year. Pruning enhances sunlight and airflow within the fruiting zone, which improves this year’s fruit quality and inhibits some disease. Improved light exposure also ensures that buds forming on this year’s shoots will be fruitful next year. Pruning removes dead, damaged, unfruitful, and otherwise undesirable wood--for instance, canes that are growing in the wrong direction or that crowd other canes. If you don’t prune, it won’t take long for your vines to creep into your neighbor’s trees!
Late February is usually a good time for homeowners to start pruning grapes because the vines are resuming active growth, as indicated by bud swell. A dormant bud nearing bud break will begin to enlarge like the picture on the right below.
This is appropriately termed bud swell. The inner bud is enlarging and will soon break free from its protective bud scales.
An ideal pruning day is dry and is followed by at least two days with no predicted rain. Pathogens, or disease-causing microbes, are carried by wind and rain and can enter vines through wounds left by pruning. By waiting for a dry period, you give the wounds time to heal before the next rain. If you cannot prune in late February due to rain, it is OK to prune in early to mid-March, before the emerging shoots reach 2 inches long. However, earlier is better to avoid inadvertent shoot breakage during pruning.
There are two basic types of dormant grapevine pruning for mature (fruiting) grapevines, spur pruning and cane pruning. Which one you use depends on the location of fruitful buds on each cultivar. Our notes for the month of January provide additional details and a link to a video on pruning.
Some grape varieties (cultivars) don’t produce fruit from buds formed close to the cane’s base. They produce clusters from buds farther out on the cane - on nodes 3, 4, 5, and 6, for example. These cultivars should not be spur pruned. To cane prune a mature vine, select from two to eight one-year-old canes (depending on available space and the vine’s age) that got good sunlight the previous season. These canes tend to have a cinnamon color.
Good canes for keeping are around the size of a pencil up to ½ inch thick. They will be woody but won’t have a lot of bark. They will be long and ideally have nodes that are fairly close together. They will be headed in the right direction, allowing them to be tied to your supports without risk of breakage. Undesirable canes are those that are too vigorous (over ¾” thick, with internodes measuring 5 to7 inches or more, and somewhat oval in shape), too thin or too short, broken, or badly damaged by powdery mildew. See January notes above for a picture.
Once you have selected the canes you want to keep, tie them to your supports with stretchy vinyl ribbon or rubber ties and cut them to approximately 12 to 14 buds long. Depending on how much room you have, you might leave them longer or cut them a little shorter. It is a good idea to tie down your “keeper canes” before making any cuts, because sometimes as you are tying the cane to a support, the cane snaps off or cracks, making it undesirable. If you have already cut off all the canes you don’t want to keep, you are left without a second choice.
For each long “fruiting“ cane (noted on the illustration below with FC), select a second cane for a renewal spur (marked as RS below). Cut this cane to a spur with two or three buds. This spur should produce shoots this year, and some of those shoots will be fruiting canes for the following year. It is helpful to protect the shoots that come from this spur by tying them to supports so that they do not get trimmed too short or become shaded out by other growth. It is also wise to leave an extra renewal spur as a backup.
Cut all the other canes back to where they emerge from the trunk. Also remove any suckers emerging below the head of the vine or from underground.
Your cane-pruned vine should look something like this.
Cultivars that produce fruit on shoots from the base of the cane should be spur pruned. When spur pruning a mature vine occupying about 8 linear feet, as a general rule you are aiming for about 14 spurs per vine (seven on each side), and two fruitful shoots per spur, each with one cluster, for a total of about 28 clusters per vine. This is just a rule of thumb that should be modified depending on how much room and what kind of trellising you have, and the age and health of your vine.
Canes that are dead, broken, crowded or headed off in the wrong direction are cut off completely. However, any cuts larger than a nickel should be made later (in May or June), when the plant is actively growing and can close the wound more quickly. Identify those future cuts with a colored ribbon so that you can find them even after the canopy has leafed out. Smaller cuts may be made now, provided the weather is dry on pruning day and for a few days afterward.
Cut one cane on each arm to a two-bud spur and eliminate all other canes on that arm. When you count the buds, however, don’t count any bud that is within ¼ inch of where the cane emerges from older wood. Such buds are usually not fruitful and are called “non-count” buds. So bud #1 will be the next bud further out. Cut after bud #2 at a slight angle so that rain and sap coming from the cut run off to the ground. Cut canes normally drip sap for days after pruning; this is not harmful to the plant. This is also a good time to cut unwanted canes that emerge from the vine trunk or from underground.
Your spur-pruned vine will look something like this:
You may have noticed the frequent mentions here of mature vines. Vines under three years of age require special pruning. For more information, see Growing Grapes, Care of Young Plants (PDF).
Other February tasks:
Weed around the vines in the walkways and clean up any grapevine debris. Natural mulch (e.g., wood chips) may be applied now or at any time, taking care to keep chips at least 6 inches from the vine trunk on all sides. It cuts down on weeds and will gradually break down, providing nutrients to the vine.
This would also be a good time to set up deer fencing, if deer are a problem. Deer love to nibble on the tender buds that will open in March, as well as the shoots that follow.
In March, buds on your grapevines will begin to swell, burst, and sprout leaves and shoots. If you did not prune in late February, prune in March before the new shoots reach two inches long.
Select a dry day for pruning, with a weather forecast for at least a couple of dry days after you prune. Pathogens travel on wind and rain, and can infect vines through pruning cuts; that is why it is important to prune in dry weather. For detailed instructions on how to prune, see the notes above for both January and February.
Look carefully at the buds on your vines. The buds you see in early March formed last year, and then went into dormancy for the winter period. Dormancy protects grapevines from winter frost. As the weather warms up, the vines start to grow again and the buds will begin to swell.
Grapevine buds pack a whole lot of potential into a tiny space. Each bud is actually a cluster of buds: a primary bud, and one or more secondary buds. If the primary bud becomes damaged, for example, by hail or a hungry critter, the secondary bud takes over and will usually push out a shoot. Be very protective of your buds and new shoots, however, especially as you prune, because shoots from secondary buds are not as fruitful as shoots from primary buds.
In this drawing you can see not only the primary and secondary buds, but also, inside the primary bud, the beginnings of a cluster and a tendril (primordia).
March is the perfect month to plan sprays for pests in your vineyard. The most widespread disease for grapes in Sacramento is powdery mildew—a fungus that damages grape vines and fruit. In table grapes it can reduce the rate of photosynthesis, which can reduce the plant vigor and resilience.
Worst of all, it also hampers the ability of berry skins to expand as the berries grow. The skins crack and scar. In many cases the berries do not ripen at all, in others the cracking allows pathogens to introduce rots that destroy clusters.
The first and second photos below show powdery mildew colonies on grape leaves and berries. They appear as a white dusty web. In both cases, the colonies are producing spores that will launch the infection cycle anew.
Powdery mildew flourishes in mild summers. Spores grow between 43 degrees F and 91 degrees F, with 77 degrees being the optimal temperature for growth. After three days in a row with at least 6 continuous hours between 70 and 85 degrees F, epidemic conditions can be assumed to exist.
Powdery mildew is so common in Sacramento that you should be ready to start your prevention and treatment program at bud break. We recommend the use of organically approved fungicides for powdery mildew control. Homeowners may spray sulfur at budbreak as a preventive/eradicant measure and later switch to another organically approved product once temperatures are consistently above 70 deg F. Examples are neem oil and highly refined paraffinic oil, which can be found in local nurseries or online. In addition to suffocating and killing mildew spores, oils also help control other common grapevine pests.
Whatever fungicide you use, always follow label instructions, particularly recommendations on appropriate spray temperatures and intervals between oil and sulfur products.
Often growers will spray for powdery mildew with a sulfur spray as a preventative and then switch to an oil or another approved product once the powdery mildew appears. Oils such as Neem Oil and JMS Stylet Oil can be found in nurseries or on line. They are organic suffocants: they coat and suffocate the spores, which kills them. They also provide some protection against grape leafhoppers—another common pest of grapevines.
Whatever you choose, always follow the instructions label and never mix sulfur and oil or use them within two weeks of each other. The combination could kill your vines. Keep spraying according to the time intervals on the instructions, until the daytime temperatures reach 95 degrees for at least 12 hours during the day. If the temperatures drop back down before you have harvested, resume the spray program.
For a list of approved pesticides for powdery mildew, and more details, see the UC Pest Management Guidelines for Powdery Mildew.
April in a healthy vineyard is a time of rapid growth. Management of vines at this time is critical to establishing good canopies. Tasks for April include:
- tie shoots to their supports
- remove suckers
Buds swell in March, and then burst with new leaves in late March or early April. Shoots, leaves, tendrils, and flower clusters begin to appear. A fruitful shoot will produce one to three inflorescences (flower clusters), depending on the cultivar and the conditions under which the buds developed the previous year. An inflorescence has many buds, each of which will become an individual flower and, if fertilized, a grape berry.
Most grape species are self-fertile, so it is not necessary to grow more than one vine to get fruit. Flowering usually occurs in May in the Sacramento area, so we’ll talk about flowering in next month’s notes.
As shoots begin to grow longer, secure the shoots to your supports with stretchy ties. Vinyl ribbons and rubber-band vineyard ties are good choices. Don't tie them too tightly; you want to keep the shoots from whipping around in the wind, but you don't want to constrict their growth (i.e. "girdle" them).
In April you may start thinning shoots lightly. For instance, remove shoots that are emerging from the bottoms of cordons. You may find two or more shoots growing from a single node. If one has an inflorescence and the other doesn’t, remove the shoot without the inflorescence. Otherwise, remove the smaller shoot(s).
At this time, you can also remove suckers, i.e., shoots growing from the trunk below the vine head. Green growth like this is easily snapped off with your fingers. Shoot removal does wound the vine, so avoid removing shoots or suckers in the rain. Please see May notes for a more complete discussion of canopy management.
We are frequently asked how, how often, and how long to water. Drip irrigation is the preferred watering method for grapes because by delivering water directly to roots, it reduces water waste and the potential for plant disease. If you have no option but to use landscape sprinklers, adjust the sprays so that water does not hit foliage and fruit.
A grapevine's moisture needs depend on several factors, including vine age, soil type, weather conditions, and time of year. In late fall and winter, moisture stored in the soil combined with rainfall generally provide enough water for dormant table grapes. At bud break, which usually occurs in the Sacramento region in late February, a vine's need for water begins to rise. The need for supplemental irrigation in our area usually starts in April with canopy expansion, peaks in July, and continues into fall as long as there is no rain and green leaves remain on the vine.
A mature, trellised vine in full Central Valley sun can consume up to 10 gallons of water per day, a little less in our area. Young, untrellised, and partially shaded vines consume less still. At summer’s peak in the Fair Oaks Horticulture Center, we water our vines four days a week, about three hours at a time, using a drip irrigation system that supplies roughly four gallons of water per plant per hour.
Table grapes, unlike wine grapes, cannot tolerate water deficits and should be watered deeply at least twice a week, particularly between fruit set and berry softening. Recently planted grapevines usually need water several times a week. Inadequate water leads to failure to thrive, reduced berry size, and, in extreme cases, defoliation. Too much water encourages excessive canopy growth and makes disease management more difficult.
If digging is difficult and a sampling probe is not in your budget, plant appearance does provide feedback on watering:
- Actively growing shoots on well-watered vines have tendrils that stretch beyond the end of the shoot. When plants are water stressed over a period of time, tendrils are short, eventually dry up, and fall off.
- On an extremely hot day in Sacramento, leaves may droop in the afternoon because they are losing water to the atmosphere faster than the plant can pull moisture from the soil. Leaves should perk up after sundown if soil moisture is adequate. Leaves that remain limp may be signaling a lack of soil moisture. Where possible, irrigate ahead of a predicted heat wave to protect foliage and fruit.
- Another sign of sustained water stress is fruit sunscald, yellowing of older leaves, and leaf scorch as early as late June.
A grapevine suffering from severe water stress, among other problems:
Also in April, continue your powdery mildew spray program, and weed, weed, weed! Weeds grow prolifically in April, and they compete with grapes for nutrients. Once you clear the area around the trunk from weeds, consider mulching with wood chips, taking care to keep chips at least 6 inches from the vine trunk on all sides. Mulch will cut down on weeds, and eventually break down to provide nutrients to the soil.
Bloom, Canopy Management, and Disease Control (Powdery Mildew)
Grapevines in the Sacramento valley usually bloom in early May. Grape flowers contain both male and female parts, so a single vine can produce fruit. Flower clusters are called “inflorescences”, and if conditions for their formation existed the previous year, they are readily visible on recently emerged shoots. Shoots with inflorescences are described as “fruitful”.
Just before bloom, inflorescences look like a collection of tiny green balls. Each ball is actually a flower bud. During bloom, the green petals that enclose the rest of the flower (“calyptras”) drop off and the stamen push upward, transferring pollen to the female part of the flower. Wind also carries pollen a short distance. Here is a picture of a cluster in bloom. The calyptras have dropped off and the light yellow stamens are visible to the naked eye.
Fertilized flowers will set, if all goes well, and become grapes. Hail, heavy rain or wind, varietal differences, and disease can all cause poor fruit set, as can heavy-handed human pruners! Be careful around the inflorescences; just brushing against them can break off flowers. Soon after pollination, unset berries will “shatter” or fall off on their own.
Blooming isn’t the only event to watch out for in May. The shoots and leaves that start growing in earnest this month are important, not only because they support fruit, but also because the nutrients they generate will return to the trunk and roots at the end of the season to support next year’s crop. That does not mean that a grapevine should be allowed to run rampant. On the contrary, by controlling canopy growth you can achieve a good crop of grapes this year, and a healthy vine that enters the dormant period with enough nutrients to produce a good crop next year.
That’s right: when growing grapes you are always thinking about two crops at the same time, this year’s and next year’s. This year’s crop developed within buds that formed on last year’s canes. In fact, if you were to dissect buds from last year’s sunlit canes and examine them under a microscope, you would see tiny, undeveloped inflorescences. Next year’s crop will develop in buds forming this year. So the goal is to create vine conditions that promote healthy fruiting both now and in the future. Canopy management practices are a critical way to achieve this goal.
Earlier we mentioned that we aim for 28 fruitful shoots on our mature, spur-pruned vines, for a total of about 28 clusters. Sometimes a vine produces multiple fruitful shoots on one spur and on another, only unfruitful shoots. In that case, we leave one of the unfruitful shoots and two fruitful shoots. Another metric we aim for is shoots per linear foot. On a spur-pruned vine, the optimal number of shoots per linear foot is about five. On a mature, cane-pruned vine, we aim for about six or seven canes total.
Downward-facing shoots, shoots that emerge from the head region, from non-count buds, and from the trunk are also candidates for removal. An exception is a shoot that could replace a dead spur, or a cordon lost due to a mechanical injury or trunk disease. In that case you might want to leave a shoot emerging from the trunk to grow out as a replacement. This is a picture of a Diamond Muscat on which a cordon was removed because it had Eutypa. A shoot that emerged from the trunk post-surgery was trained as the the replacement cordon on the right.
In late May you can also start watching for the formation of lateral shoots, i.e. shoots that emerge from where leaves attach to the shoot. On the picture below, the shoot on the left is a lateral shoot.
It is a good idea to remove laterals unless they are needed on the sunnier side of your vine to shade clusters. As a general rule, remove less foliage on the side of a vine that gets the hot afternoon sun.
May also offers perfect conditions for powdery mildew to run rampant in grapevines. As mentioned in our April notes, when temperatures rise into the 70’s and stay below 85 degrees F for 6 consecutive hours, 3 days in a row, plant disease experts consider a powdery mildew epidemic to be in place and recommend a regular spray program. Oil-based products like neem oil and all-season horticultural oils provide control as long as coverage is good and application frequency follows label instructions. Oils also help control a major nuisance pest of local grapevines, grape leafhoppers. These tiny, light-colored insects flutter from the canopy when disturbed and are often confused with whiteflies.