Growing the Perfect Grape
Nature and the grape grower work hand in hand to grow high-quality grapes. Obviously, the location of the vineyard is hugely important (try growing Cabernet Sauvignon in Alaska!), but a savvy grower can make the most of a harvest even when nature throws some curveballs her way. If the following things are in place, however, a grower's job becomes a little easier.
If a region's spring and summer temperatures never top 50 degrees, the vine will never wake up from winter, much less bear quality wine grapes. Even if the region is sunny, you need heat.
During the growing season itself, if temperatures hover below 50 degrees or above 95 degrees, photosynthesis virtually stops. Photosynthesis is the process by which energy from sunlight allows for the manufacture of sugars in green plants, including grapevines. A vine without these sugars is like a car without tires — useless. Excessive heat or cold can frustrate this process.
Some grapes can tolerate warmer temperatures, such as the thick skinned Cabernet Sauvignon grape, but more delicate grapes such as Pinot Noir and Riesling like cooler weather. If you attempted to grow Pinot Noir in the hotter northern regions of the Napa Valley, for example, grape acid levels would be difficult to maintain and the grapes themselves could dehydrate and shrivel into raisins. Good for eating; bad for winemaking.
Why is it so important to maintain good levels of acidity in wine grapes?
Think of Coca-Cola without the carbonation. It is flat and syrupy. Wine made from grapes harvested with low acid levels is flabby, noticeably alcoholic, and lacks spark.
Sunshine is necessary for photosynthesis to occur. Even in areas with stretches of cloudy days in the summer, grapevines can usually get the light they need. Excessive cloudiness becomes problematic if rain begins to fall from them, especially during fertilization or harvest.
Sunshine is also important for color development in grapes, especially red grapes. One of the reasons that a glass of Shiraz is dark as ink is because growers allowed their grapes sufficient sun exposure. Growers may have to remove leaves from around their grape clusters so that the sun can have this effect on the fruit. Excessive sun, of course, leads to raisins.
Grapevines do need a certain amount of water to live, much less bear grapes. If that water reaches the vines in the form of rain, then approximately twenty-seven inches of it should fall per year, although some vines get by with less. As important as rain is, however, if it falls at the wrong time of the year, such as during fertilization or right before harvest, it is problematic.
The ideal time for rain to fall is in the winter and early spring when the vines are dormant. If it falls during fertilization in late May or early June, then grapecluster development will be affected. If it falls too close to harvest, then it can literally dilute the wine and rob it of its intensity. If the rain is particularly hard, then the grapes can get knocked off the vine or the grape skins can be punctured, causing rot.
Many wine regions depend on irrigation to make up for a lack of rainfall. For example, the Swan District in Western Australia, quite possibly the hottest grape growing region in the world, would not be on the wine map without irrigation. The desert-like wine regions of Eastern Washington State also depend heavily on irrigation.
If you have the ideal levels of heat, light, and water for grapevines but not the proper soil, then you might be in for a short career as a grape farmer. Here are just a few of the questions you need to ask yourself about your soil before you charge ahead with planting grapes: Is it shallow or deep? Is it rocky or clay-heavy? Is the soil acidic? Answers to these questions can make or break your vineyard plans.
First of all, grapevines need three major nutrients (nitrogen, phosphorus, and potassium) and six minor nutrients (magnesium, manganese, iron, zinc, copper, and boron) to live. If a soil's pH is too low (acidic) or too high (alkaline or basic), then the availability of these nutrients, along with the vine's capacity to absorb them, will be affected. In addition, if your soil has an excess of limestone, for example, then the vine will not be able to absorb iron, leading to a nasty condition called chlorosis.
Second, if you know about phylloxera, you know that you need rootstocks for your Vitis vinifera vines. Not all rootstocks, however, are created equal. If your vineyard is near a river, drought is probably not your foremost concern, as your soil will be moist. Using a rootstock that reaches deep into that wet soil will deliver an excess of water to your vine, causing it to grow so vigorously that grape quality might be affected. Using the American Vitis riparia would be a good move in this case, as its roots are shallow, thus managing the vines' water intake.
Napa Valley has more than 30 distinct soil types, which, combined with variations in climate from north to south, produce a wide variety of wine styles.
On the other hand, if your vineyard has a rocky soil and barely gets the necessary amount of rainfall, then you should plant your Cabernet Sauvignon vines on Vitis rupestris stocks, as these reach much deeper into the soil than Vitis riparia, thereby snatching up precious extra drops of moisture.
Finally, soil content determines how growers train their vines. If the soil has a high composition of gravel, sand, and loam, and the climate is hot, then the grower should train his vines such that the grapes do not develop too close to the ground. The heat absorbed by gravel, sand, and loam rises up from the ground and ripens the grapes much faster than the grower might prefer.
Conversely, if the soil has a high concentration of clay and the climate is somewhat cool, then grapes should be closer to the ground, as clay does not absorb as much heat as gravel, sand, and loam, and some extra heat might be needed to get riper fruit.