The Riverbank Grape (Vitis riparia) is a woody vine that can grow up to 15 m in length. It uses tendrils to climb trees, shrubs, and fences. Riverbank grape is native to North America and is found extensively throughout Canada, as well as the North Central and Northeastern United States.
I. Appearance and Characteristics
Vitis riparia Michx, with common names riverbank grape or frost grape, is a vine indigenous to North America. As a climbing or trailing vine, it is widely distributed across central and eastern Canada and the central and northeastern parts of the United States, from Quebec to Texas, and eastern Montana to Nova Scotia.
In the wild, the vine thrives along exposed areas with good sun exposure and adequate soil moisture, such as riverbanks, forest clearings, fence lines and along road sides. The species has adapted to a variety of soil chemistries.
There are reports of isolated populations in the northwestern USA, but these are probably naturalized. It is long-lived and capable of reaching into the upper canopy of the tallest trees.
Riverbank grape is a translation of the scientific name Vitis riparia; rīpārius means “of riverbanks” in Latin, deriving from rīpa “riverbank”.
Mature vines have loose, fissured bark, and may attain several inches in diameter. Leaves are alternate, often with opposite tendrils or inflorescences, coarsely toothed, 5–25 cm (2.0–9.8 in) long and 5–20 cm (2.0–7.9 in) broad, sometimes with sparse hairs on the underside of veins.
Vitis riparia is functionally dioecious. The inflorescence is a panicle 4–15 cm (1.6–5.9 in) long and loose, and the flowers are small, fragrant, and white or greenish in color. V. riparia blooms sometime between April and June and in August or September produces a small 6–15 mm (0.24–0.59 in) blue-black berry (grape) with a bloom, seeded, juicy, edible, vinous in flavor, lacking the “foxy” characteristics of Vitis labrusca, but usually quite sour and herbaceous.
Vitis riparia has a wide range and may deviate considerably in detail from the above general description. White berries, perfect flowers, large clusters, large berries, and sweet fruit are among the known variations. However, some observers consider such variations as evidence of natural hybridization with other species of grapes.
II. How to Grow and Care
Sunlight
Riverbank grape requires at least 8 hours of full sun each day throughout its growing season. This applies to both outdoor and pot-grown plants.
Watering
Once a riverbank grape sprouts, it should be fertilized and thoroughly irrigated. After that, irrigation is not usually required, so long as the soil 20 cm below the ground remains moist. If the soil is not obviously dry before or after flowering, less water is better to avoid spindling. Once the fruit begin to expand, an outdoor riverbank grape should be watered thoroughly every 10 to 12 days.
Once the grapes start to color, cut back on water to prevent the fruit from cracking and dropping. After harvesting, a thorough watering is essential to restore the plant’s vigor. Water thoroughly once more before the soil freezes.
As for a potted riverbank grape, keep the soil moist inside but slightly dry on the surface. In regions with hot summers, watering should be done every morning and evening. During a rainy spell, potted plants should be moved to a more sheltered location to reduce exposure to rain.
Soil
Riverbank grape requires deep soil with good drainage; ideally, a sandy loam. The optimum pH value ranges from 5.5 to 7.0. Make sure that water does not accumulate around the plants after rainfall.
Fertilizing
Riverbank grape is a deep-rooted plant, so it is very important to measure the soil’s nutrients and apply a suitable base fertilizer before planting. Some common grape-specific basic fertilizer supplement measures are:
- Phosphorus deficiency: apply phosphate fertilizer (0-45-0) or bone meal (1-11-1).
- Potassium deficiency: use potassium sulfate mixed with sandy soil.
- Magnesium deficiency: apply an additional layer of Epsom salts.
No matter what the soil condition may be, only a small amount of fertilizer should be applied in the second year after planting a riverbank grape. Apply this during the budding period. Dig a circular furrow 1.2 m away from the base of each stem. A compound fertilizer (10-10-10) is best, but avoid over-fertilizing, as this can lead to spindling and reduced resistance to cold.
If you choose to use organic fertilizer on a mature riverbank grape, apply it every winter. If a chemical fertilizer is selected, apply it to the plants after flowering.
If new shoots grow slowly during the growing season and leaves are either losing their green color or are easily burned by the summer sun, your plant may have a potassium deficiency. This can be treated with a top-dressed potash fertilizer; the amount applied depends on the degree of deficiency.
Among the trace elements, zinc and boron are most important to the riverbank grape. A zinc fertilizer can be top-dressed to the leaf surface a week before flowering, while a boron fertilizer should be applied to leaves 3-5 days before flowering. Please refer to fertilizer instructions for specific dosage.
Planting Instructions
Adjust the pH of your soil before planting a riverbank grape. Add lime to decrease acidity or sulfur to increase it. Make sure your planting site is well-ventilated with plenty of light, and is located on high ground. This helps prevent water accumulation. Before planting, turn the soil deeply to ensure that all weeds, residual roots, and large stones have been removed.
Ideally, planting holes should be around 30 cm in length, width and depth. Space plants 2 m apart, with row spacing at 1 m. After planting, fully composted farmyard manure works well as mulch.
One year after planting, stake your riverbank grape so that it grows upright. Insert a bamboo cane 30 to 40 cm into the soil about 15 cm from the seedling. Tie on any new shoots with loose slipknots, ensuring that they are evenly distributed.
A trellis for riverbank grape can be built both vertically and horizontally. For a vertical trellis, the lowest level should be at least 91 cm above the ground. If a horizontal trellis is adopted, its height should be over 2 m.
Pruning
Pruning your riverbank grape is very important to maintain growth and prevent diseases and pests.
Bud picking and pinching. As soon as mature plants start to bud, keep only one strong bud on each node of the strong branches, picking off any buds. Remove overgrown or stunted branches, axillary shoots, and tendrils as soon as possible to facilitate ventilation and transmission of light. New riverbank grape shoots must be pinched so that only 4-8 leaves remain above the spike.
Flower thinning. The number of flower spikes is usually determined according to the species and the weight of the spike. For small-spike species of riverbank grape, 2 spikes can be left on each fruiting branch. For medium-spike species, 1 spike can be left on each fruiting branch. For large-spike species, no spikes should be left on the new vine near the main vine.
Flower-spike thinning should be carried out before flowers start to bloom to avoid excess nutrient consumption. Remaining spikes need to be pinched off by 1/4 of the length of the spike tip. The secondary and tertiary spikes that grow later can be thinned in time.
Winter pruning. For newly planted seedlings in their first two years, all axillary shoots should be cut off to keep the trunk strong. Only the trunk and leaves directly attached to the trunk should be left. Once the trunk grows 91 cm tall, the top tip should be pulled horizontally and tied to an iron wire at a higher level.
After the first two years, select the robust fruiting branches close to the trunk for cutting back. Each pruned spur should have 2 or 3 buds. After new shoots sprout in the spring of the following year, the shoots at the upper part of the plant are the ones that will bear fruit. Then the rest of the branches can be cut off.
When you winter prune the following year, a strong branch near the base of the trunk should be selected for short-tip pruning as a new fruiting branch, ensuring that 2 or 3 buds are once again retained. Repeat in this way, and robust fruiting branches can be kept while the year-by-year outward movement of fruiting parts can be prevented. When a wound caused by winter pruning is larger than 1 cm, a protective agent should be applied to prevent bacteria infection. Any cut branches and tendrils should be burned in bulk.
Propagation
The most common propagation method for riverbank grape is through hardwood cuttings. The best time to cut these branches is at the end of the winter, before the soil thaws. The lignified (rigid and woody) branches should be as thick as a pencil and 50 cm long. When taking cuttings, the cutting edge should be 3 cm away from the top bud, and the cutting surface should be slightly oblique. Wrap fresh cuttings in wet soil, and then put them in a bag and store them in a refrigerated chamber until the soil completely thawed.
Insert cuttings vertically into the planting hole when planting, leaving only the top bud exposed out of the soil surface. Firmly fill the hole with soil and water, keeping the soil consistently moist afterwards. After the cuttings take root, the seedlings can be transplanted once the soil thaws in the spring of the following year.
III. Uses and Benefits
- Ornamental uses
Riverbank grape is an attractive vining plant that brings beauty to garden spaces and is a statement piece in cut flower arrangements. In the garden it grows on arbors, trellises and fencing for growth support. If this vine grows up into nearby tree or plant canopies, it will smother other plant life, so give it space and direction.
- Other uses
Perhaps the most significant agricultural usage of V. riparia is as grafted rootstock for Vitis vinifera. Important advantages of the use of V. riparia (and hybrids between it and other Vitis species) include resistance to phylloxera and adaptation to variant soil types.
Due to the extensive cold hardiness and fungal disease resistance of this species, it has been used extensively in grape breeding programs to transfer cold hardy and disease resistant genes to domesticated grapes. The French-American hybrid grapes are notable examples of these attempts. V. riparia has been used extensively for over a hundred years to create hardy hybrids.
Many V. riparia hybrids are currently being used and investigated by plant breeders and in breeding programs such as those conducted by the University of Minnesota’s horticulture program in an effort to make a commercially viable wine grape that can survive the northern climate of the Upper Midwest. Examples of commercially important cultivars with significant V. Riparia ancestry include Baco noir, Marechal Foch, Triomphe d’Alsace and Frontenac.
While V. riparia shares many important characteristics with its cousin, Vitis vinifera, the small size of the berry (making it prone to predation by birds), the high acidity of its fruit (often up to 5% titratable acidity), the intense pigment of its juice, and the presence of herbaceous aromas in wine produced from it have made it unusable on its own for commercial viticulture.
These grapes are sometimes used to make flavorful homemade jellies, jams, and wine.
IV. Harvesting and Storage
To ensure the best flavor, pick only fully ripe fruit. The simplest and most reliable way to confirm maturity is by tasting. Clusters can then be cut off with scissors and stored. Berry quality declines rapidly in later stages of maturity, and rotten fruit can damage the riverbank grape.
