I don't know about the patio but the grape vines need full sun & good air circulation & even then may get mildew, grape vines are messy so not great to walk under or have patio under as you will be cleaning up mess all the time to say nothing of bird droppings. Where is water coming from that gets the area wet?? Improper grading, rain, septic tank etc. Not likely to go away.

I'm not 100% sure where the water is coming from. I think it's a combination of the fact that the backyard slopes towards the house, and some rain gutters are probably clogged and part of the rain falling on the roof are falling on the ground behind our house. This happens only during the rainy season, of course.

Too bad about the messiness of grape vines. I do love the idea of having a grape vine overhead.

You're safe growing grapes in Fremont. When I was a child there in the late 50's and early 60's (Glenmoor Gardens neighborhood, on Logan Drive), at least one of the local farmers grew grapes. My friend GH had a whole field of grapevines behind her house.

We bought strawberries and Bing cherries from farmers' stands, and saw apricots being dried on wooden trays in the orchards. Just half a block down the street from us was a field which in different years was full of sugar beets or ... cauliflower or broccoli -- can't remember which; later a grade school was built there (the architect was the father of my friend Irene). Oats grew all around our church.

There were three families who owned the large truck farms: the Fudennas (I went to school with one of their kids), the Morriseys (pretty sure about that name; my mother was a friend of theirs), and maybe Williamses.

Kimber raised chickens in the foothills near Niles (we had lived there for a couple of years in the mid-50's, and our across-the-street neighbor was their veterinarian). A nursery next to our subdivision grew shrubs; they had an old adobe building.

There was a big NILES in white on the hillside, similar to the Hollywood sign (not vertical, but either painted on the ground or in lime); I don't know which sign came first, but in the very early days of movie-making, Niles was in competition with Hollywood.

Major non-agricultural businesses included a small steel mill. And Leslie Salt harvested salt from the Bay.

Hard to believe, huh? In those days the population was only about 20,000.

Grapes are fun and will grow in your climate, but they're bare and ugly for over half the year. What's the point when it's as likely to be warm enough to sit outside in March as it is in July?

I'm partial to passiflora vines - evergreen (and vigorous, so support them well). You'll have to search a bit to get the edible fruiting ones - some of them fruit but it isn't good quality - but the bonus is you'll get beautiful butterflies from February thru October - it's the sole food source of the Gulf Fritillary butterfly.

You'll need to test your soil before making the decision to add any sulphur to counteract lime. Unless you're growing acid-lovers like rhodies and pieris, I wouldn't worry about it unless testing shows your alkalinity is off the scale.

You might want to put your money towards looking into a rainwater catch system. Incorporating the storage tank (they're big, needing at least an 8x8 space) works better when you can hide it with intentionally-designed landscaping. Rainwater catch systems can capture 18K gallons in an average year and around 8-10K gall even in a bad year.

To handle water coming down from the hillside, would a French drain help? You'll need to figure out a good place for it to end, as you don't want to be responsible for flooding a neighbor's house (you'd be legally liable and have to pay for remediation).

I think if you solve your water problem, you'll be able to put in a simpler patio (meaning, set in sand or gravel) without needing it to be non-permeable. You also need to remember that if you're growing a fair amount of veggies, they aren't xeric at all - they pretty much all need good-sized regular doses of watering. So a rainwater catch system might sizably reduce your EBMUD bills as well as helping dry out your crawlspace.

Checking your gutter system and clearing out clogs and debris build-up is fairly easy to do, also. You'd be amazed what blows in.

Thank you for your responses.

We're leaning towards using natural stone (like slate or sandstone) for the patio and seal it to reduce water seepage.

As for growing a grape vine, we've decided to move it out of the patio to near the fence, where we'll build a smaller arbor to help with privacy as well. As of now the patio is going to be uncovered.

If you do elect to use a mortared slate or flagstone over a concrete base, make sure it is sloped away from the house, and that you do have sufficient positive slope away to drain the extra runoff a patio will generate. If the slate/flagstone is not mortared, then sealing the surface of a stone patio will not reduce your water infiltration below the house. It sounds like a major source of your moisture under the house is due to downspouts off the roof that do not direct the water sufficient distance away from the house foundations. You will need to direct water away from the house by connecting the downspouts to a drainage system at a minimum, and may also need to address seepage from the hillside behind the house by a french drain as well. A lot of the times with newer homes in subdivisions, the lots are graded so relatively flat that there is insufficient slope for positive drainage out to the street from the backyard, and unconnected downspouts only make the problem worse. As well, many homeowners are their own worst enemies in making the sideyard drainage worse, by failing to maintain a good drainage swale out to the street.

It is unlikely that creating a sealed surface immediately adjacent the house will reduce your moisture problem under the house if you don't solve the runoff from the roof.

Hooking up downspouts to a water storage system is not necessarily a bad idea, but with our concentrated rainfall in winter months only, and long dry season with no rain in the warmest months, any water you may be able to save is pretty expensive and not sufficient to last more than a few weeks or perhaps a month into the dry season. Rainwater capture systems make more sense economically where there is consistent or at least periodic rainfall throughout the year, or during the months when plants need to be irrigated, which is not the case in any part of California. I'd suggest it makes a lot more sense to redirect the water away from the house, and switch solid drain lines to perforated pipe with a filter fabric sleeve once you clear the house and reach the front yard, where the perforated pipes can be used as a weep line to recharge the water table once the lines get at least 10 feet away from the house, with an overflow line continuing to the street for extreme high rainfall events when the water recharge lines might not be able to discharge fully into the soil.

As to growing grapes over an arbor, this can be a very nice feature in hot summer areas like most of Fremont, and you may actually appreciate the shade in summer. Concord grapes are the most readily available grape at nurseries, but you can also get better varieties if you buy them on-line, or go with types that are used commercially for table grapes or wine making. As others have mentioned, the leaching of lime from concrete is not the issue with soil problems as much as making sure that the area where the grapes are to be planted is not full of leftover construction debris from house construction, and that any concrete work does not use the planting areas as the location to dispose of waste concrete and water used during the pouring of the concrete base. Soils in the SF Bay Area are generally in the neutral range, unless you are contending with bay fill soils, which often are salty as they are dredged from the bay itself. Get a soil test done if you think you need one, that will give you the best information on what your soils may require for best growth of plants you want to grow.

What they said--I don't think you address your water problem by putting an impermeable surface outside your door.

I agree with those that say putting in a solid surface will increase your water problem not solve it. If the ground slopes toward the house you will always have water problems. A-- because the water will run towards the house and B--the water coming off of your house has no where to go.

I would address the water problem before thinking of adding a patio. What you need is a dry well. This is basically a large hole in the ground that is filled with large sized gravel that catches the excess water and holds it, then disperses it into the ground. There is much more to it so you'll have to look up how to do it.

A dry well will help with resale if you ever decide to sell.

Then you can put in any kind of patio you want

bahia,

Thanks for the detailed response. I agree with you and those who say that my water problems are elsewhere. It is possible that it's a combination of the existing pipe being clogged up due to years of neglect, and some spouts not draining into the existing pipe. I hope the problem is not due to the existing pipe having a big hole somewhere along the way to the front of the house, causing all the water to discharge somewhere near the house. If so we'll have to tear out the concrete in the side yard, replace the pipe and relay the concrete. A lot of work and more expenses, but fixing the drainage issues has to be my priority. The landscaping is secondary.

I'll stop focusing on a non-permeable patio and instead go with what we like.

That's a brilliant idea my dear, Fix first the water problem before you can move to the next step. It is important to prioritize what is necessary. Thanks.