Here at GlenLyon, March bottling has been successfully completed and now it’s time to switch from my Winemaker Hat to my Grape-Grower Hat! Growing grapes requires a wonderful gift each year from Mother Nature … rainfall. This past year, however, our Mother was very stingy.
The average rainfall in Sonoma County normally registers around 36”; this season, we’ve had less than half that amount — about 16”. A drought year (or subsequent years) will mean a huge difference to our all-important water tables, the amount of water in our ponds, reservoirs, streams, and rivers. This directly translates to the amount of water that is available to use for our homes, our businesses, our livestock, and our agriculture. Growing grapes and making wine requires water, and this much-less-than-normal year means we need to conserve even more than we have in the past. Plus, the drier our landscape, the worse it is for the upcoming fire season — but that’s another conversation.
When to start irrigating? How often? How much water?
Regardless of the year, the same questions loom for our farmers: When do we need to begin irrigating the grapevines and how much water does each vine need?
Most farmers in our area water their grapevines using drip irrigation. Why drip irrigation and not overhead Rain Birds that blast an intermittent stream of water over a large area? The simple answer is conservation. We’d rather drip the water directly onto the root system of each vine to conserve both our well and aquifer water, and not waste that valuable resource. (You may have noticed that some vineyards look like they are using both types of irrigation because you see Rain Birds spraying water early in the morning. Those sprinklers are used for early-morning frost protection, and if they are blasting water during the day, the farmer is probably testing the system to make sure the equipment works.)
How do we know when the vines need water?
So, how do we decide which day is crucial to begin irrigation, how often we should irrigate and how much water we should use each time? Years ago, farmers would simply compare the data from their rainfall and watering history. They’d see how much rainfall they’ve had, feel the ground, look at the cover crop and note the newly emerging green growth tips of the canes and then try to answer those questions. Accurate? Not by a longshot, so we’ve invented tools to help us make those decisions.
What tools do we use?
We use two of those tools here at GlenLyon. The first are “moisture probes,” PVC tubes with sensors inside that are permanently dug into the ground at different depths in various spots throughout the vineyards. I drive the ATV up and down the rows, stop at the designated vines, hook a portable monitor up to the two leads of each probe and the number on the monitor tells me the amount of soil moisture in the ground at 8” and at 18”. The second tool is my trusty “pressure bomb,” which is a self-contained (and very expensive) unit the size of a small suitcase that has a refillable nitrogen tank built-in (see above right). With that unit strapped to the back of my ATV, and after the new growth canes are about two feet long, I drive up and down the rows and stop at designated vines throughout the vineyard. I count down to the 6th or 7th leaf from the end of a growing cane and, with a razor blade, I cut the end of the stem (petiole) that attaches the leaf to the cane. I then insert the cut end of the petiole into a detachable lid, tighten down the rubber grommet around that upended protruding petiole, insert the leaf portion in the built-in pressure chamber, bayonet lock the lid down onto the unit and turn on the nitrogen from the built-in tank. Attached is a magnifying glass, and, as the gas pressure slowly increases and pressurizes the enclosed area around the leaf, I simply look at the magnified end of the cut petiole. When a bubble of water appears on the cut end of the stem, backwards away from the leaf, I turn off the N2 and a gauge tells me how much pressure it took to push that water backwards up into the cut end of the petiole. Depending on that number, I know how thirsty (or not thirsty) that grapevine is. I repeat the process between noon and 1:00 every four or five days to different designated typical vines throughout each watering block in both vineyards (we have a total of 7 different blocks of vines, all with different needs). Using both these tools, I can monitor both soil and plant moisture. Then I compare my notes with previous years’ notes to compare the data and come up with a decision. If it is time to begin watering, I will then program our (very elaborate) watering manifold (see below) to water each block of vines at a specific day/time and, again, make notations so this new data can be used for next year’s decision-making. Because there is no unwarranted irrigation, these two tools save us (and our environment) many, many gallons of valuable water each year.
What about “deficit irrigation”? Or “dry farming”?
You hear a lot about “deficit irrigation.” Some farmers and winemakers say that it’s a good idea to severely stress out the vines to force the roots to go deeper to search for water, and that added stress on the vines will ultimately produce better wine. True? Maybe. Maybe not. (I personally think fast-growing vine canes in the heat of the summer are a lot like kids … if your kids are desperately thirsty, you don’t tell them to wait a week to get a drink of water.) There are also some farmers who believe in no irrigation at all (“dry-farming”), preferring that the vines only rely on yearly rainfall, but that would be very “iffy” during this much-less-than-average rainfall season. Even the French (who for centuries did not allow any vineyard irrigation), now allow a controlled and regulated drip system.
When do you stop irrigating?
After harvest and before the seasonal rains begin, we encourage the vines to go dormant, so we stop watering right after harvest; the date depends on the yearly rainfall Mother Nature gave us. Absolutely everything in farming wine grapes depends on the year’s weather, and the amount of rain is a huge factor. Whatever happens in the vineyard directly influences the quality of the finished product — the wine in your bottle.
A very wise farmer once said to me: “Growing grapes is like dancing with Mother Nature. But remember that YOU are Ginger Rogers and SHE is Fred Astaire. She always leads!” I like that.
Welcome to spring! Now just drink it!
-Squire Fridell, Glenlyon Winery
It takes a long time to grow an old friend.