A grow tube keeps plants warm during cold weather and humid when it's hot and dry, enabling the plant to form strong roots and balanced growth which results in full fruit production a year earlier than normal. Using a grow tube minimizes watering requirements as the plant consumes much less water than plants exposed to wind and direct sunlight. Wind dehydrates leaves which respond by growth shut-down to conserve water.
Choosing a Grow Tube
Grow tubes are available in triangular, square and round configurations and a variety of heights, diameters and colors. The best grow tube will be round, allowing for greater growing area inside the tube. Vineyard use has determined the best tube diameter for optimum stem size and root mass to be between 3.5" and 4.5". Grow tube heights of 30" to 36" help suppress lateral shoot growth while the main shoot grows quickly and vine training is only required after the shoot exits the grow tube.
Tube color has an effect on the temperature inside the tube with darker colors generally being warmer. Temperatures inside the tube on a sunny day can be 10 to 20 degrees higher than the ambient temperature. Tube color may also have an effect on how the plant allocates its growth resources. Pink/beige tubes seem to optimize the ratio of light frequencies plants need for photosynthesis.
Split grow tubes allow for easier plant maintenance than solid tubes and can be removed without detaching the vine from the trellis.
When and How to Apply a Grow Tube
Grow tubes can be placed on dormant plants in cooler climates. In hot climates apply tubes when there are at least 2 fully expanded leaves on the plant. More than one shoot in the tube may cause problems in establishing your vine so keep only the strongest shoot and cut out the weaker ones. Remove all lateral shoots.
Apply a split grow tube with the seam parallel to the row and away from prevailing winds. Make sure to affix a good quality support stake to the outside of the tube. If you live in a hot area place the stake to block some of the afternoon sun and heat. In cooler areas place it on the north side of the tube.
Mound 3" to 4" of soil around the base of the tube. This helps to secure it, keep out any cool air running along the ground and minimize the possibility of herbicide sprays and dust from entering the tube.
Care of Grapes in a Grow Tube
Grapes started in grow tubes need less water. Grow tubes tend to recycle water by attracting condensation, reducing water requirements. Do not water directly into the grow tube as this will result in overwatering which leads to poor root function and poor vine performance. Water only when the soil at the base of the grow tube both inside and outside is dry. Once the shoot grows out of the tube train it to your trellis at once, otherwise it will flop over the side and may be damaged.
When cold temperatures arrive, remove the grow tube. Don't leave the tube on over winter as heat build up inside the tube will cause the plant to come out of dormancy early and perhaps winter kill. Remove the tube at least 3 to 4 weeks before the first frost to allow adequate time for the plant to harden off. There is no further growth benefit to using the grow tube in the second year.
Tips on Growing Grapes:How to Plant and Care for Grape Vines
Resources: Northwest Berry & Grape Information Network
Wines & Vines, David Gaines
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