Knowing that the tree will be in close range to the garage , 6-10 feet, then I would think that a small growing tree would be more site appropriate. These trees may be a good source to check out: Acacia vestita - gracefuly weeping silvery cut leaf in form with soft yellow late winter flowers grows to about 16 ft tall and about the same in width. Cercis canadensis Forest Pansy - nice burgundy heart shaped leaves that flutter in the wind. the tree grows to about 20 ft. tall and about 16 wide. Deep pink flowers in late winter /early spring . Fruitless Olive - Swanhill - can get to 25 x 20 but easily can be kept smaller with once a year pruning. Arbutus unedo or the larger growing A. marina ( maybe too large for your location - Madrone Callistomon Cane's Hybrid. - gorgeous soft pinkish flowers cascading down from a 15 tall x15 wide tree. I have this growing in my Marin county yard and always receive nice feedback out its shape, form , foliage and flowering. A trip to Flora Grubb Garden Nursery in SF will further help you to find some great trees or The Dry Garden on the Berkelely/Oakland line.

Let's consider two issues in turn: what kind of soil, and then how much. The quality of your produce is directly related to the quality of the dirt they grow out of. This makes sense, because plants consist of energy from the sun, oxygen and carbon from the atmosphere, and matter from the soil in which they live. Therefore, it is worth your while to make sure that your beds are full of good dirt. You want to pay attention to a few factors in garden soil, mainly nutrient content and drainage. Once you know what you want, you can buy cheap ingredients and mix them to get what you desire. Base: good ol' dirt A good base for a garden soil mix is the cheap topsoil that you can get at your garden center. Lots of stores sell topsoil for cheap in the spring, like maybe $2 or less for a 40-pound bag. That seems like a lot of dirt, but it's really a negligible amount once you start filling in your bed. Nutrients: compost & peat moss You also want to have a lot of nutrients, so it is a good idea to add in some compost. It's great if you're making it, if not they sell it at garden stores. It's incredibly rich, so it's okay to mix in only a bag or two per raised bed. Peat moss is also a good idea, as it is full of organic matter. It comes in big bags, and is really concentrated so you don't need all that much to have an effect, maybe half a bag for a medium-sized bed. Drainage: sand/vermiculite & peat moss You also need drainage, which refers to the ability of water to seep out of the topsoil. (This is what distinguishes a swamp or marsh from "good" land where you can grow things like tomatoes or corn.) This is aided by little holes in the soil. Since water seeks the lowest level, raised beds inherently have good drainage, but you can make the situation even better. It's a good idea to break up your substrate (the area under your bed) pretty well with a fork or spade before building your bed. You also want to make sure to mix in your added soil with some of your substrate, because an abrupt border can lead to problems with compaction: sometimes roots will never penetrate the substrate if it's not mixed, and drainage will be reduced. It's a good idea to mix some sand into your bed's soil to increase drainage; vermiculite (the white chunks in potting soil) also works, but then it looks too much like potting soil and not enough like a garden for my tastes. The light texture of peat moss can also aid quite a bit in creating better drainage, in addition to the nutrient benefits. That said, it will take a LOT of dirt to fill your raised beds. I built some beds that are 5' wide, 10' long, and 1' high. Each one required a bag of peat moss and 1,600 pounds of topsoil! That's 40 bags of that cheap topsoil, which even at a low price came out to hundreds of dollars for a few beds. I highly recommend against using potting soil or your bill will easily stretch into the thousands of dollars. The way to do it on a budget is to: 1) buy cheap materials 2) mix it yourself 3) use topsoil that is on sale, or maybe even free from a local landfill 4) you can even fill the bottom with straw: a straw bale is pretty cheap and gets you a lot of organic matter. It will biodegrade in a year or two if it's buried at the bottom of your bed, it will increase drainage, it will not hurt your plants, and it's a lot easier to move than dirt. In Scandinavia, they traditionally grow potatoes in straw without even any dirt, and they do fine (plus then they come out totally clean!) 5) don't use potting soil! unless it's old potting soil that you have tossed in your compost pile or something I hope all that helps -- good luck building! Also, it might be a good idea to line the bottom with chicken wire or hardware cloth if you have problems with varmints in your area (so they can't dig up into your bed), or to line the bottom with landscape fabric (to prevent grass etc. from growing up into your bed)

I have found kimmsr's info about clay to be very true. We have very dense clay around here, so raising beds was my best option over the short term. I put some pine bark fines (very fine mulch) in my beds, then added our clumpy, sticky clay, then another layer of mulch. I let it sit for a few weeks until the clay was rendered "mixable" by the even moisture level it attained when mulched. I combined it well with a garden fork, then added in some compost and other good stuff. Clay and mulch made up the bulk of the mix, and plants have done very well in it. Now, two seasons later, earthworms and cultivation have turned it into very nice, friable soil that bears no resemblance to its humble beginnings as mid-Atlantic clay! In Arizona heat, I would imagine the water-retentive qualities of clay would be a plus? If money is less important (and the idea of filling that much volume with potting soil makes me think is may be), you could just hit up a local garden center and buy bagged or bulk mixes. I have found raised beds to be rather forgiving of different soil compositions due to the drainage you get above ground level. This post was edited by jadie88 on Sun, Apr 13, 14 at 6:56

Following up a few months later... The experiment with perennial tomatoes did not work out. They pretty much shut down after the pruning. Still, home-grown tomatoes at Christmas is pretty cool. This year, I cut way back on the number of plants in the greenhouse, from six tomato plants to two, and it's much more manageable. I've also tried to layer the plants in the greenhouse bed: Strawberries on the bottom, peppers in the middle, and tomatoes up high. This does not work well. The tomatoes and peppers have very deep roots. Strawberries are shallow rooted, so you wind up either overwatering the tomatoes or underwatering the strawbs. And even though you get strawberries a month before you'd get them outside, there's no point in having strawberries in the greenhouse when you have perfect strawberry weather outside. Next, maybe carrots and beets for the lower stratum. The peppers I planted are the Spanish Padron, which have become very popular. They have a reputation as having variable degrees of spiciness ("unos pican, otros no"). The deal with these guys is that they're quite hot *once they're mature enough to set seed*. So...if you're going to grow these guys...harvest early. They're best when they're tiny.