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Use of Grapevine Grow Tubes

The use of “mini-greenhouses” around plants began in Great Britain in 1979. Graham Tuley wrapped polyethylene around conventional plastic mesh guards in an attempt to increase the growth rate of newly planted trees. This led to the development of the tree shelter. There are around 5 million tree shelters in use each year (Kerr, 1996). Tree shelter use began in 1987 in the United States in Eastern forests. Eastern grape growers began using tree shelters on Concord grapes in 1990 (personal communication, Treessentials Company). Australian researchers also began adapting this technology to grapes in 1990 (Due, 1990). Today, there are several different companies that market grapevine grow tubes. Some of the names that are most likely to be seen advertised are ‘Supertube’ by Treessentials Co., ‘Blue-X’ by Blunt Enterprises, ‘Slide Tube’ by Quiedan Co., ‘SnapMax’ by Treemax and ‘Gro-Guard’ by Gro-Guard.

Providing a shelter around young grapevines has many advantages. A shelter protects vines against small mammals, herbicide drift, desiccating winds and weather damage. It can also reduce evapotranspiration, increase growth rate and reduce labor for vine training. These factors often make grow tubes a good choice for new vineyards and especially for replacement vines in established vineyards. With proper grow tube use, a vineyard can be in full production a year earlier than normal. Differences Between Tubes: Grow tubes are available in square, triangular and round configurations and in several different heights, diameters and colors. Some tubes are preassembled and others require assembly. Round or triangular tubes are better in windy areas than square tubes because they do not offer as much wind resistance (Kerr, 1996). Cross-sectional area inside the tube is also important to plant growth and round tubes have a greater area than triangular tubes for the same diameter tube. This factor seems to be most important in hotter climates.

Some tubes are solid and others are split down one side. Split tubes are more versatile than solid tubes, since they allow plant maintenance during the growing season and can be removed without taking the vine off the cordon wire. This means that the grow tube can be left on the grapevine until late in the season to obtain the maximum benefits. Split tubes also require less space to store in the off season.

A grow tube should incorporate ultraviolet light blockers and last 3 to 5 seasons. When calculating tube cost, you need to factor in the life expectancy of the tube. Many of the better grow tubes cost around $1 to $1.25 a tube in the Eastern United States. If you prorate this over 5 years, the yearly cost is only $0.20 to $0.25 a tube, excluding storage.

Tubes are available in several heights ranging from 18 to 36 inches. One advantage to using a tube over 24 inches is a reduction in labor required for vine training. A tube height of 30 to 36 inches is probably best for most applications. Lateral-shoot growth is suppressed while the main shoot grows quickly in the tube. Vine training is required after the shoot tip exits the grow tube and lateral-shoot growth begins. Internode lengths are often longer in the portion of the trunk covered by the tube due to rapid growth. This can result in fewer water sprouts in subsequent years and a further reduction in labor.

Tube diameter is critical for the production of strong vines with thick trunks and large root systems. Treessentials, Company of St. Paul, MN has developed the “Supertube Clipper”. This is one of the best grow tubes available and was developed after years of research using different pigments, dyes and filters. Studies conducted at California State University, Fresno in the 1995 growing season, on Cabernet Sauvignon vines, using the “Supertube Clipper” have shown that tube diameter affects vine mass. Vines grown in milk cartons grew for 139 days before reaching topping height. Vines grown in 2.5″ tubes never reached topping height. Vines grown in 3.5″ tubes reached topping height in 96 days and vines in 4.5″ tubes reached topping height in 108 days. In addition, vines grown in 3.5″ and 4.5″ tubes had greater stem diameter and root mass than the vines grown in milk cartons. Although the vines grown in the 4.5″ tubes required 14 more days to reach topping height, they produced double the stem and root mass of vines grown in milk cartons and a larger stem and root mass than the 3.5″ tubes.

The effects of tube color on vine growth are difficult to ascertain. Two tubes, produced by different companies, that appear to be the same color could have different pigments, dyes, resins, UV adsorbents, etc. that affect plant growth. Tube color does have some effect on the temperature inside the tube with darker colors being generally warmer. The temperature inside a grow tube on a sunny day appears to be 10 to 20°F higher than the ambient temperature. It is thought that the high temperature inside the tube may help retard the growth of pathogenic microorganisms (Due, 1990). The lack of plant pathogen growth in grow tubes has never been fully explained. One would expect that pathogen growth in the hot, humid environment of the tube would be extreme. However, with several million grow tubes in use around the world; pathogen growth has rarely been a problem. This is not to say that vines should not be checked on a weekly basis, because localized problems do develop.

Growth rates:
Growth rates of almost two inches per day have been reported using grow tubes in Australia (Due, 1996). At this rate of growth, a vine can reach a 42 inch cordon wire in three weeks. However, growth rate is variable and depends on water, sunlight, temperature, soil conditions, rootstock and age of plant. Obviously, a one year old plant will grow much faster than a rootling, due to its larger root system. A good grow tube will increase the carbohydrate storage in the root and main stem. This is indicated by an increase in stem diameter and root mass and is critical to producing earlier and larger, sustainable yields.

A major problem growers encounter when using grow tubes is that the plants grow faster than the trellis system can be established. It is important to remember that two years of training can be done in the first season when using grow tubes. A training wire must be in place 2 to 3 weeks after the tubes are installed and the entire trellis must be in place before the end of the growing season.

In trials in a grower vineyard in Northwest Arkansas, there was rapid initial growth using “Supertube Clippers”. The tubes (24 inches tall and 3.5 inches in diameter) were placed on five cultivars: Cabernet Franc, Cayuga, Chambourcin, Cynthiana and Vignoles. Control vines, with all lateral shoot removed, started growing slowly but reached the 6 foot cordon height on 4 out of 5 cultivars by the end of the growing season. Internode lengths at a 24 inch trunk height were about 1.5 inches longer on plants with grow tubes than the controls. There was no difference in internode lengths at a trunk height of 48 inches. It was possible to establish eight feet of cordon, at a 6 foot cordon height, on three of the five varieties tested when using the tubes.

Tube installation:
Grow tubes are applied after normal vineyard planting. It is important that the vineyard be established correctly. Grow tubes do not correct for poor soil conditions. Soil must be corrected for pH problems, compaction, poor drainage and fertility prior to planting vines. Always follow your nursery’s planting recommendations.

Grow tubes should be applied when there are at least 2 fully expanded leaves in hot climates. In cooler climates or in areas where dormant season planting is done, the tubes can be placed on dormant plants. It is not desirable to leave two shoots in a tube. This defeats the purpose of the tube and one shoot will be dominate. In addition, this may cause problems in quickly establishing a uniform vineyard. If it is necessary to leave two shoots in a tube, use the largest tube available.

Split tubes should be applied with the seam parallel to the row and away from prevailing winds. Mound 3 to 4 inches of soil around the base of all grow tubes. These actions will help secure the tube and minimize the possibility of herbicide sprays and dust entering the tubes.

When installing grow tubes on plants that are several inches tall, lateral shoots should be removed. When lateral shoots are removed, no further training is required until the shoot tip exits the tube. There must be support in place when the plant exits the tube. Otherwise, the plant will sustain damage as it droops over the side of the tube.

When using grafted plants, make sure that the nursery used a standard grafting wax. This wax is white or pink and flakes off when scraped. If the nursery used “cheese coat” or “cheese wax” do not use grow tubes on the plants. This type of wax has a clear and greasy appearance and is adsorbed into the bark. Cheese wax has a low melting point and could melt, if a grow tube is installed, allowing the graft union to dry.

Good quality stakes, that will last the season, should be used. The necessary stake length depends on tube height as well as soil density and wind intensity. A clay soil will hold a stake better than a sandy soil. In general, the stake should be at least six to eight inches below the ground and extend at least two inches above the tube. If the vine will be trained to the stake, the stake should reach the cordon wire. The stake should be applied on the outside of the tube. The cross-sectional area inside the grow tube is necessary to maximize vine growth. In hot areas, the stake can be placed to block some of the afternoon sun and heat. In cooler, or cloudy areas the stake should be placed on the north side of the plant.

Care must be taken, with new plants, to avoid diseases. Green plants should be sprayed with a broad spectrum fungicide before installing tubes. Botrytis problems can sometimes occur with spring plantings due to humid, cool conditions. Powdery and downy mildew has also been observed in some vineyards as temperatures increase (Due, 1990, 1996).

Grow tubes must be removed before cold temperatures arrive. If tubes are left in place through the winter, the heat inside the tube will cause the plant to come out of dormancy early and perhaps winter kill. Tubes should be removed at least 3 to 4 weeks before the first frost. This will allow adequate time for the plants to harden off. Irrigation: Vineyard irrigation is not usually necessary in the Eastern United States until vines exit the grow tube. Tubes tend to recycle water by attracting condensation and reducing evapotranspiration. This effect is enhanced when mulch is used, since mulch helps retain moisture.

Overwatering leads to poor root function, and vines in grow tubes sometimes perform less well than control vines because the grow tube delays soil drying (Due, 1996). Extreme care must be exercised when using grow tubes to replace vines in established, irrigated vineyards. It may be necessary to plug emitters near the new plant to avoid overwatering. Do not water directly into a grow tube because this will result in overwatering. Shoot growth should be monitored on a regular basis in both new and established vineyards. When shoot growth slows, more water should be applied. However, make sure that the slow shoot growth is not due to water saturated soil. The soil at the base of the grow tube both inside and outside the tube should be moisture deficient before watering.

Conclusion:
Grow tubes can speed the early grapevine growth. They protect against wind desiccation, damage from herbicide, small mammals and weather damage. Installation and irrigation are key factors in getting the most vine growth when using grow tubes and must be carefully monitored. Under Eastern growing conditions; it is recommended to use a 3.5 inch diameter tube at least 30 inches long.

Literature Cited:
Due, G. 1990. The use of polypropylene shelters in grapevine establishment — a preliminary trial. Australian Grapegrower Winemaker. 319(6):29-33.

Due, G. 1996. Vineguards: How to get the result you want. Australian Grapegrower Winemaker. 389(5):32-6.

Kerr, G. 1996. The history, development and use of treeshelters in Britain. In: Proceedings of the Tree Shelter Conference. (J.C. Brissette, ed.) 1995 June 20-22, Harrisburg, PA. Gen. Tech. Rpt. NE-221. Radnor, PA: U. S. Department of Agriculture, Forest Service. Northeastern Forest Experiment Station.

Personal Communication. 1996-1997 Treessentials Company, Riverview Station, P.O. Box 7097, St. Paul, MN 55107.

Dr. Gary Main, Research Associate, Institute of Food Science and Engineering. University of Arkansas. 272 Young Avenue, Fayetteville, AR 72704. This paper was presented at the Viticulture Science Symposium and Workshops. June 5-6, 1997 Florida A&M University, Tallahassee, Florida