I would like to build a raised veggie garden...the only spot available is on a slab of asphalt...this is obviously not the most healthy option...would a barrier make this a possibility...or should we attempt to remove the blacktop altogether(costly and labour intensive)
just use large planters - make sure there are drain holes in the bottom though! those big tubs with the handles on them (a lot of people use them for the kids toys) are really good for using as planters (you'll just need to add some drainage to them).
I'm with Joclyn, raised beds are the way to go! You can build fully raised (ie on little feet) beds out of wood - cedar is nice, and so are the other softwoods. If you layer these by height, you can effectively double or triple your planting space. I have done this in my own yards when they're tiny or inconveniently paved; I line the whole schmozzle with landscaping cloth, which is water permeable but keeps the dirt and roots in. I also have painted the insides of the boards with a dilute white glue solution to successfully waterproof them and prevent warpage. A bit more elbow grease than buying premade planters, but the final look is fantastic and you have complete control over what the planters look like as well as how big and deep they are. This way you can put your deeper planters, ie for root crops like beets and carrots, which like at least 2' of soil to grow happily in a planter, on the bottom tier, then narrower and shallower 1' deep ones above for things like bush beans and tomatoes, and finally the smallest, 6 - 8" deep one on top for leafy greens - your salad patch. I've had great success planting peas and other vine foods in the bottom tier and training them to grow up the legs and across the frontage of the other two tiers. If you're interested I can send you my plans for these; they use stuff that is easily available at Rona or one of the other big-box construction stores, and take about a day of construction if you have basic power tools (ie a saw and a drill). If you have hand tools only, how long it takes will depend on how fast you are with a hammer. I have done it both ways. Alternately, if you want a "funky" look for your garden, you can make planters out of an old clawfoot bathtub (sometimes available for a steal at the architectural reclaimers.) Just drill four or five new holes in the bottom, then paint the outside fun colours using enamel paints. Or mosaic it with tile chips (if you ask nicely at Rona, they'll just give you their broken tiles.) Read on to see why I'm suggesting this.... I have a friend who did a whole bathroom suite of plantings on top of asphalt - a number of pedestal sinks full of trailing fuchsias line his driveway, and in the yard proper there's a pair of bathtubs of veggies, and three toilets, one each in trailing strawberries, vine tomatoes, and sweet potatoes. His whole small yard is paved, none of the bathroom fixtures match (the toilets are, respectively, pink, avocado, and white) and he's got them arranged quite artistically. Last I talked to him, he was looking for some more bathtubs to expand his vegetable garden.
