you don’t plant what you think you want to get for yield; unless you have some secret powers or can say ‘nature happens’ and let it go. you plant a bunch more as you think you want and if surplus happens you can preserve it, you give it away, you compost it.
raised beds are like using a large open bottom container. if you have poor soil you can create a shallow (root depth) raised bed, if you have problems reaching the soil you can create a high raised bed (a few feet high).
if you have poor drainage then a raised bed will improve that, if you make the bed have drainage.
if you have poor soil with OK drainage then you might clear out some poor soil in an area and bring in or make soil, this will give a level bed. you could bring in soil or make it using the sheet mulching method on level soil on an area larger than you want, this will give a mounded bed. you could enclose just the area you need bringing soil or making it in a raised bed.
Square Foot Gardening - is a great book on raised beds. The original book came out 20 years ago. This is the updated (2005) version.
http://www.amazon.com/Square-Foot-Gardening-Garden-Space/dp/1579548563/ref=sr_1_2?ie=UTF8&qid=1296331166&sr=8-2
Covering it with an opaque tarp will cool the soil, not warm it, though it will kill the weeds to a certain extent by depriving them of light. It won’t take care of all of them, though. To solarize the soil, you would want to use clear plastic, water the ground well before spreading it out, and seal the edges by holding them down with a heavy pile of soil to hold the hot, moist air in. That will warm the soil and kill weeds.
If your ground is sandy and gravely, it’s probably pretty well draining, yes? To test this, dig a small hole, fill it with water and see how long it takes to drain. Obviously this can’t be done until the ground isn’t frozen, heh. If the soil has good drainage, don’t bother digging it up and replacing it, but build a raised bed or box on top, and fill that with your topsoil. This will save you a lot of work and expense, and you’ll have a nice, neat garden bed to work in. If you want, you can line the bottom of the box with landscaping fabric, which will prevent most weeds from coming through (for a while, not indefinitely) but will allow water to drain through. Even if you don’t have good drainage this can be done, but you’ll have to make sure that the water has somewhere to drain to so that your bed doesn’t end up sitting in a puddle.
A raised bed can be built out of lumber, most easily in a square or rectangular shape, or you can make them almost any shape you want using stones, concrete blocks, or make your own out of cement and milk cartons or the suchlike. Two feet deep would be plenty, though you can get away with less than that if you’re not trying to grow deep-rooted veggies. I would make them only as wide as you can reach into the middle from the edges, so that you don’t have to step onto the soil and compact it while weeding or tending your plants.
There is no such thing as too many home-grown tomatoes. Too many zucchini, now, that’s not only possible, but inevitable. 
You probably won’t have any difficulty finding takers for your surplus. If you put them in your compost, beware of including the seeds, or you’ll have a compost pile full of tomato plants. My mom had so many volunteer plants in her greenhouse due to fruit falling on the floor, and she couldn’t bear to kill them once they’d sprouted, so they tended to take over. But in the process, she managed to accidentally breed an absolutely sugary, succulent variety, just through open pollination between the ones she’d planted and their offspring and their offspring’s offspring and so on. Some of the ones that came out of the mix were very strange and not very tasty, we made sure to dispose of those before they spread their seed around, but there were some that were obviously a mix between cherry and a larger variety that were absolutely wonderful, and just the right size for skewering and grilling.
Wanted to amend an earlier post – if you build a raised bed on top of the existing ground, you will DEFINITELY want to smother the grass and weeds with something. I mentioned landscape fabric because it will last for a few seasons and is relatively good at suppressing weeds while letting water through, but layers of newspaper, cardboard or other such materials will work as well. Organic materials will become soil eventually, by which time the weeds will with any luck be gone.
I also second the “sheet mulching” recommendations, it’s a good way to suppress weeds and create soil.
Here are some good instructions:
Basic principle is a series of overlapping layers (“lasagne”) of organic material (paper, cardboard, natural fibre carpeting, etc.) to stop weeds getting through, something rich in nutrients (manure, kitchen scraps, grass clippings, etc) to feed the microbes and plants, and a deep top layer of loose organic material (straw, wood chips, compost, etc) that you can plant directly into and which will quickly turn into soil.
Start with a layer of rich raw nutritious material to encourage worms and other microbes to come join the decomposition party, and then a layer of overlapping sheet material to suppress the existing plants, then keep alternating layers of whatever you’ve got to work with. Make sure you leave no gaps between your sheet material when overlapping them, and if you notice weeds coming through later, layer some more sheet material such as newspaper on the spot and cover with more mulch. After you’ve pulled up as much of the offender as possible, of course, so it doesn’t just push the mulch out of the way in its search for sun.
Put anything that might contain unwanted seeds, such as lawn cuttings or hay (as opposed to straw), in the bottom layer to stop them sprouting, and put woody material such as chips in the top layer so that the nitrogen in the air can help break them down. If wood is mixed into the lower layers it will take longer to decompose, and will steal nitrogen from the rest of the soil while doing so, to feed the bacteria and other microbes doing the work.
Raised bed and Square Foot Gardening™ are just versions of French intensive gardening. The most important of FIG isn’t the plants, it’s the soil and the beds it’s in.
Prepping for FIG is a royal pain,
Double digging a '15x’24 plot is crazy. Double digging is crazy. The exact same effect can be achieved by building raised beds.
The raised beds serve multiple purposes;
You don’t need to double dig, you loosen the topsoil add compost and mix (you can use power tillers for this but every thing I’ve read suggests that they do more damage to the soil stricture than they’re worth, OK for the initial bed prep but after that a fork (preferably a broadfork) at the end of the season to turn the beds mulch in, worms will actually do most of that for you anyway) then just top off the bed with more good compost. Over time a raised bed stops being about growing in soil and becomes growing in compost (fall comes and you start wondering how many of those those bags of leaves on the street you can use, grass clippings are green gold).
It gets you closer to the ground without bending.
It keeps the bed soil where you want it, in the bed.
They keep you out of the bed and on the paths between the beds, walking on the bed compacts the soil - compacted soil doesn’t drain as well as loose soil.
They drain better, you could actually build a raised bed on concrete, the bed soil will only hold the water it will hold the rest just drains away.
They drain better in the spring, you can work the soil earlier.
They warm up earlier so you can plant earlier.
The bed wall give you places to attach things, trellises for tomatoes and other climbers, cold frames and high tunnels both extend your growing season, you can start earlier and the first frost ain’t the end of your plants (you can build a high tunnel with PVC and plastic sheeting).
They can be made of almost anything, there are complete kits, kits to hold wall material together (board lumber and concrete pavers), treated lumber, untreated lumber, concrete retaining wall blocks, “cinder” blocks, etc.
Have I sold you yet?
The beds should be no wider than twice your reach, 3 or 4 feet, so you can harvest from both sides. No longer than 8 - 12 feet, makes it easier to get around the beds. Height depends on material, a single 2x6 or a concrete block is enough to start. Higher and tend seedlings and harvest root crops with out hurting your back (drive-by gardening too!). Pathways should be no narrower than your lawnmower, unless you want to go all out and make them permanent, weed-block fabric and non-composting mulch (I.E. no shredded bark!) light colored stone reflects light onto the plants, red (like shredded red rubber) makes tomatoes happy.
The Square Foot Gardening™ thing is all about the intensive part of FIG. A 3x8 bed for tomatoes or corn would have one or two close rows of plants (down the middle) . . . and a whole lot of area for weeds to grow between the row and the bed wall. So FIG says plant that area, plant it hard. Enough low growing veggies that weeds can’t see the sun. At the beginning of the season things like lettuces, then, now that the primary plants are getting taller things like bush beans. The basic idea is that there should always be something planted everywhere in the bed. You can buy the book but all it really does is give you a better idea of just how much closer plants can be to each other than the seed packets recommend. There’s less actual “bed” in your '15x’24 foot section of yard but you’ll get the same amount or more from the beds with much less labor.
More links. This is a beautiful example of the technique.
CMC fnord!
I don’t wait for my tomatoes to ripen on the vine; once they start to show a tinge of yellow, you can take them in and ripen them in a drawer.
Speaking from long experience, yes there is. Why waste time on space on excess plants, that could be used to grow other things?
The first year I’d invest in a few really big plastic pots, good potting soil and a bag of slow-release fertilizer. Try determinate varieties that don’t need a bunch of staking. Also, if you don’t generally eat a whole tomato at one sitting (we don’t), smaller salad/grape/cherry varieties are your best bet.
Also, many gardeners out there would kill for very sandy, fast-draining soil. It’s a lot easier to improve (with organic matter) than thick, gooey clay soils.
Successful tomato growing (including planting times, selection of varieties etc.) also depends heavily on the climate where you live.
I knew someone on a gardening mailing list (way back when those were the major online communities other than usenet) who used to take her excess zucchini, put them in brown paper bags, and leave them on her neighbors’ doorsteps in the dead of night.*
*“I am the Midnight Zucchini Distributor what distributes at midnight!”
No, no you have not. It’s obvious that you’re knowledgeable and passionate about this. You raise some very good points and this method has distinct advantages. There are also some issues that make it unattractive to me at this time. Maybe a year or three down the road I’ll do something like this but right now, for better or worse, it’s not going to happen.
First, I’m really trying to minimize my short term, up-front cost of the project. I can borrow my dad’s tiller to cultivate the soil. Compost is available from the recycling center and I can get sheep manure from a farmer friend of mine. Both are available to me for free on a “you shovel it - you own it basis”. I have clear plastic instead of my tarp to use if you feel I’m better off with it. With my plan, imperfect though it may be, virtually my only out of pocket expenses are for the tomato plants, fuel for the tiller and (probably) a little chemical fertilizer. Landscaping stones or timbers to contain the bed costs money. Clean, ready to use, soil to fill the beds costs money. Right now, given my current financial situation, I’d rather spend my time and muscle.
Second, right now, I’m really only interested in growing tomatoes and maybe a few beans. The beds you describe are a marvel of efficiency and versatility. Versatility that just doesn’t interest me at the moment. Again, maybe a year or three down the road I’ll do something like this but right now, for better or worse, it’s not going to happen.
I appreciate the info and I thank you kindly for your efforts but I think this kind of project isn’t in my short term plans.
Yeah, probably too passionate. :smack:
Lost in there were a couple of points that really will help you.
You don’t need, or want, to work the entire 15’x24’ into “garden” just the rows you’re going to plant in. (I started out working the whole plot, then I got smart and only worked the actual area I was going to plant. Went from two days of hard labor to buying plants in the morning and having a finished vegetable garden before dinner.)
Formal “boxed in” beds are nice but it’s the raised part that makes all the difference. A bed shaped mound of compost is all you really need.
With what you’ve got available; I’d decide where I want the rows to be, go down the rows with the tiller to loosen up the soil (no need to go more than 12" to 18" wide for the row), work in some manure and compost with the tiller to make the worms happy, cover the row with a mound of compost* 12" to 18" deep, 18" or so wide, plant the mound, mulch throughout the season with grass clippings or straw to keep the weeds under control.
*If it’s finished compost, stuff that looks like black potting soil not chopped up leaves (that’s mulch that someday will grow up to be compost), that’s better than anything to grow in.
CMC fnord!
For what it’s worth, a single 4x8 sheet of plywood can make a single 4’x8’ bed, that is 1 foot tall. Rip (4) 1 foot strips, the long way, then cut one of them in half. Find an old 4x4 that someone is discarding and cut 1 foot blocks. Simply use the blocks in the corners, and nail the ripped plywood.
Total cost for 48 sq ft of garden is less than $20. Fill with the compost, manure, and some soil, and you’re gardening. Expand the empire as you have funds, or materials.
Don’t use treated plywood for it if you’re planting food.
Well, the arsenic and other toxins are supposed to leech into the soil contaminating the plants and harvest. However, there are other studies that say that the most migration into the soil is less than 2" surrounding the treated lumber so use it at your own risk.
I built mine from a double layer of treated landscape timbers. They are attractive and play an important role in my landscape. I don’t have single boxes in rows. I built an “L” shaped configuration that I love. It’s three stepped layers tall and I combine flowers and vegetables together. I’ll have to see if I can find a picture.
Mel Bartholomew (Square Foot Gardening) was my inspiration. Love it love it love it!
Hard to get CCA (chromated copper arsenate) treated lumber these days,
But the new stuff ACQ (alkaline copper quaternary) (and IPS CA-B and CA-C (copper azole) marketed widely under the Wolmanized brand in North America, and the Tanalith brand across Europe and other international markets) has other problems,
From here.
I’d love to use those plastic and wood deck boards (Trex et al.) but the stuff’s so damned expensive. 
CMC fnord!
Are you planning to leave the tarp covering the ground for months? That might not be so great for the soil, because all the oxygen will get used up, and you will get anaerobic bacteria growing, and lose all the worms. Better to use mulch to keep down weeds. You can also plant legumes as a cover crop, to help build up the soil. Dig them in at the end of autumn.