From a Correspondent:
I planted grape vines this last spring. What type of care do they require? What type of fertilizer do I use and how often, etc., etc.
Joanne, Sun Lakes, Ariz.
Good morning Joanne,
Grapes are fairly simple to care for in the home garden, provided we have realistic expectations. Commercial grape growers and wine makers have very precise and sometimes complex routines that they follow, but for the rest of us, a few simple steps are enough to get some nice table grapes on a yearly basis, and an attractive landscape plant to go with them.
And just so you know up front: you can throw your grape in the ground, fertilize when you remember, water when it looks like it needs it, prune only when it threatens to take over the world, and still have a big green vine. But if you want a little civility (and grapes to eat), keep reading.
The three primary nutrients that grapes need are nitrogen, zinc, and potassium. Chances are your soil has enough potassium, so we'll concentrate on the first two:
- First year: One tablespoon of nitrogen in the form of ammonium sulfate in February, and another about now, early May.
- Second year: Two tablespoons of ammonium sulfate each month from February through June.
- Third year and beyond: The vine is maturing, so give each vine one cup of ammonium sulfate in February, one cup in March, and a third cup after bloom, early to mid-May. Also, give each vine one-half of a 5-pound bag of zinc sulfate with the February feeding, and the other half with the March feeding.
These nitrogen levels are based on the generally poor level of nitrogen in desert soils. If after the first or second feeding of the season you find that your vines are healthy, green, and vigorous, halve or skip the rest of the season's nitrogen, to avoid over-fertilizing your grapes. Some people recommend a foliar spray for the zinc, but I find it easier to apply the zinc to the soil. When you fertilize your grape, first water, then scratch the fertilizer into the soil, and then water again. Watering first helps to prevent fertilizer burn.
Moisture is important for vine and fruit development, so be certain that the soil never dries out completely from the time the leaves open until harvest; keep it moist, but never wet or soggy. Use several inches of organic mulch, such as small chipped bark or wood chip, to conserve water and to even out fluctuations in the soil moisture. Before you water, move aside some of the mulch; if the soil is still damp, then wait to water. Most of the soils I've encountered in Sun Lakes are a fairly heavy clay-loam, with good water-retention properties, which is good news for you. That means you shouldn't have too water too often, but you will want to water slowly and deeply each time you water. Use a soil probe to be sure that the water is getting down to a depth of two feet or more when you water; once you figure out how much water it takes to wet the soil to that depth, you then just always use the same amount.
Whole books have been written on pruning grapes, but I'll get you started.
For the first year, just let the vine grow; all those leaves are helping to build up a good root system for next year's big push. Whatever you're going to grow the vine on, have it in place before the second year's growth begins. This winter, when the vine is dormant, select one or two strong canes and prune off the other canes. Gently guide and tie your selected cane or canes onto your trellis, then cut them back to buds at about the height where you want the vines to branch. In their second year, the vines will branch from this point and form what are called laterals, which you can loosely tie to your trellis as they grow.
Think of these laterals as your main structure or scaffolding; they will determine the overall shape of your vine. As a home grower, you can have as many laterals you wish at whatever height you wish, but too many will over-burden the vines and be a mess to prune.
In the third year, branches will grow from these laterals, and in future years you will prune these branches back to two or more buds, depending on what variety of grape vine you have. Of selected varieties that do well in the Desert Garden, 'Thompson Seedless' and 'Black Monukka' are said to be best with what is called "cane pruning," while 'Muscat of Alexandria' and 'Perlette' are said to be better with what is called "spur pruning." A confession: two years out of the last six I pruned my 'Thompson Seedless' with the wrong method and couldn't see a scintilla of difference. Or even a whit.
This should get you into year three with some happy and healthy vines. If you need more complete pruning instructions then, send me another note and we'll get into the nitty-gritty world of pruning grapes. I might even draw a little picture.
I hope this helps,