Jonathan Sachs wrote:

sumone wrote:
Where are you?

I'm in the Sacramento area. Winters are cool and rainy, with
occasional frost; Summers are hot and dry.

Perfect for grapes... should be many winerys about.

What is the soil like?

Generally deep, fairly heavy loam left by an ancient sea bed; but our
yard is heavily landscaped, and I don't know the history of the soil
that was used for fill. It looks like the native soil but I can't be
sure.

Even if the builder scraped off some top soil it wouldn't have been
much and wouldn't much matter... grape roots go deep, very, very deep.

What kind of grapes are these?

Really doen't matter what kind at this point.

When we moved in two years ago I collected samples from each vine and
took them to one of our local Master Gardeners (part of California's
ag extension program). I got some identifications, some tentative
ones, and some of "Gee, that's interesting, but..." Almost every vine
seems to be different. I can't find my notes at the moment, but the
ones I'm working on now appear to be wine grapes.

...if the vines are on rootstock?

No idea. I see no evidence of grafting scars, but I'm not sure what to
look for, and perhaps the vines are too old for them to be visible.
Many of them are over an inch thick at the base.

The ag extention would be your best source in the area for how to
grow/prune grapes, wtf didn't you ask???

An inch diameter indicates a very VERY young grape vine, couldn't have
been been more than the diameter of a pencil when planted 2-3 years
ago, probably planted shortly prior to your arrival. Grape vines grow
extremely fast, that's one of the reasons they need to be pruned twice
a year and the second pruning very severe.

What did the leaves on the dead
plants look like last year, or the last year that they had leaves?

Obviously they would look like grape leaves. duh

I think they were long dead when we bought the property two summers
ago.

If you arrived in the summer there would have been leaves... seems to
me you never even looked at those grapes till very recently.

The vines are so tangled together that it's hard to tell which
ones are dead and which ones aren't. The one I mentioned, at a corner
of the shed: I suspected it was dead, but I wasn't sure until I
started cleaning up dead wood a few days ago.

Odds are very little of the vines were actually dead and it's very
difficult to kill a grape plant from mere neglect... as I indicated
previously you should lop off all but about two feet of the trunk (now
is a good time). And as soon as they bud out in spring erect a
trellis/arbor of some type, very important that grapes are trained.
There's tons of information on the net about how to grow grapes.

I've grown grapes most of my life but since I retired I gave it up,
growing grapes is extremely labor intensive, never mind what to do
with them... one measely vine will produce minimally 100 pounds of
grapes, ripening all at once. And where you live it will be
impossible to sell them let alone give them away. I can't imagine why
any homeowner in that part of CA would want to grow grapes in their
yard.