I don't usually disagree with Dan about any of the advice he provides, but I am going to offer a different opinion this time :-) One of the primary benefits of raised bed gardening is that it enables the gardener to garden under soil conditions that makes inground gardening challenging - like with heavy clay soils, poor drainage, inappropriate pH, etc. So the 'need' to incorporate the existing, underlying soil into the raised bed soil does not necessarily track. By definition, raised beds offer improved drainage over inground soils -- just by virtue of the soil level being raised but also because raised beds do not offer impervious containment and because the soil tends to be of fluffier, lighter texture; i.e. 'fast draining'. So the mixing of the two soils is not a requirement. However, if your raised beds are not deep, the underlying soil easily workable and you are interested in planting deep rooted plants or veggies, incorporating the two may be desirable. As to what to fill them with, it depends on what you can find easily, locally and inexpensively. If you need a quantity, bulk soils will always be cheaper than bagged soils. And most bulk soil providers will offer something called a 'garden planting mix' or a '3-way mix' that is pretty much an ideal blend for a raised bed. Typically it is a mix of loam (sometimes 'topsoil'), some sort of compost or composted manures and a drainage enhancer - could be bark, sawdust, sand, even perlite. In lieu of that, try a 50-50 mix of 'topsoil' (or whatever generic soil they offer) and compost. And make sure the stuff is well-blended. Because raised beds typically offer quite fast drainage compared to inground soils, moisture retention is sometimes critical. In hot weather, raised beds do tend to dry out faster. Mulching is typically the best way to reduce evaporation and conserve moisture but frequent watering may still be required anyway.

You didn't state your zone location. In my area of western WA with dry summers & wet mild winters drainage is utmost because things rot in our cold wet soils if I don't amend soil for fall/winter crops. We need to add lime yearly due to the heavy rain leaching the soil. You could consult the county extension gardening resources or consult a local independent nursery for more information about the soils in your area. Mixing it up now sounds like a good idea. Mulch plants after planting. Add compost after harvest. Keep putting organic matter back in on top of the soil & the worms will work it in the rest of the way. You won't have to dig through & mix it all up again. The beauty of raised beds is that you only dig once. If you're planting transplants you could just part the layers & plant them. Seeds will need fine soil so they can break through. Chunks make it more difficult for them. I agree about allowing space for mulch to hold the moisture & provide some frost protection if your climate warrants.

I have a lot of eucalyptus trees growing along the fence of the units next door. I have a passion-fruit growing in a pot and it was matted over with the white roots; the pot was on a concrete slab so the roots could not have travelled from the tree. A friend of mine said the Chinese pay money to buy these roots as it is good for the soil but I believe they are choking the young trees including my passion fruit although it is not dead. I made a raised garden and placed a weed protector half a meter high on the sides yet the raised garden is full of it and it has attached itself to the weedmat.

I made a real nice raised bed garden to plant some veggies in and then bought a bunch of potting soil at Walmart, finishing it off with many bags of EarthGro Potting Soil and EarthGro Steer Manure and "compost". My epiphany came too late after I'd spent a lot of time, and money when I checked with SourceWatch:http://www.sourcew atch.org/index.php/SourceWatch and googled in EarthGro. The following is what I found: "Paul Sellew is s a CEO of Harvest Power. Paul also founded Earthgro, which is the second largest producer of biosolids-based lawn and garden products. Paul was a senior executive with Synagro. He also founded International Process Systems, AllGro, Environmental Credit Corp, and Backyard Farms.[1]" Just in case you didn't know, biosolids is another name for sewage sludge. I don't know about you, but I am not going to eat vegetables grown in sewer sludge which contains God only knows what besides human crap. Now, I'm going to have to use my nice raised bed for Remedial plants such as sunflowers to decontaminate this soil if it's ever to be used again: http://en.wikipedia.org/wiki/Phytoremediation In view of this information, I'm wondering just how many of the non-organic fruits and vegetables are being grown in soil contaminated by biosolids, aks toxic sewage sludge and sold to Americans without our knowing it? " http://www.sourcewatch.org/index.php/Biosolid... ; Biosolids is the Orwellian PR euphemism for toxic sewage sludge. The name was created and chosen in a PR contest by the lobby association for sewage industry, the Water Environment Federation (WEF). For more background see also The EPA's plan to bypass opposition to sewage sludge disposal and You say biosolids, I say sewage sludge. There is now a SourceWatch Portal on "Biosolids" Beyond biosolids, the sewage sludge industry now puts its waste product into bags labeled "compost" and promotes them through US Composting Council, BioCycle and other front groups and partners. Beginning in the 1990's the WEF, with the active encouragement and approval of the Environmental Protection Agency, pushed for the disposal of sewage sludge on farm land after bans were imposed on dumping it in the ocean or incinerating it. The name change of sewage sludge to "biosolids" was crucial the image makeover for sewage sludge, a classic industry-government campaign of greenwashing to change the public perception of toxic sewage sludge from an accurate one of "hazardous waste" to the misleading image of biosolids representing safe "beneficial reuse," responsible "recycling" and healthy "organic fertilizer," lately including the ruse of sewage sludge as "organic compost." A list of just some of the hazardous chemicals and pathogens found in sludge can be found in the article Sludge contaminants. Sludge contaminants include Dioxins and Furans, Flame Retardants, Metals, Organochlorine Pesticides, 1,2-Dibromo-3-Chloropropane (DBCP), Naphthalene, Triclosan, Nonylphenols, Phthalates, Nanosilver, and thousands more substances. "Sewage is the mix of water and whatever wastes from domestic and industrial life are flushed into the sewer.... We must note that, though the aim of sewage treatment is to produce clean water, it is never to produce 'clean' sludge. Indeed, the 'dirtier' the sludge - the more complete its concentration of the noxious wastes - the more the treatment has done its job.... very waste produced in our society that can be got rid of down toilets and drains and that can also be got out of the sewage by a given treatment process will be in the sludge. Sludge is thus inevitably a noxious brew of vastly various and incompatible materials unpredictable in themselves and in the toxicity of their amalgamation, incalculably but certainly wildly dangerous to life." [1]