Be sure to add water-retention crystals. (Lowes has them under the brand Agrosoke -- look in the fertilizer section.)I've started using them in pots, planters -- even in planting holes. They make a very significant difference in the moisture level of soil. Somewhat expensive, but trust me -- a little goes a LONG way.

The FAQ link at the top of the main Square Foot Forum page has a detailed entry on how to fill the beds. Expanded shale and coir seem to be the non-compost (and natural or low-impact) additives of choice. However, I grow in what amounts to 100% compost, though that includes an occasional bit of perlite or vermiculite that I'd used for rooting cuttings and tossed in the pile when it was no longer sterile, etc.

an_ill-mannered_ache 9a
Thanks so much for giving me the name and location of those water retension crystals. I learned about them earlier this year and haven't known their name so ahven't been able to find them.

ray_scheel
I will definately check out that FAQ - thanks!

The 'official' square foot mix is 1 part peat moss, 1 part vermiculite and 1 part compost.

The compost is the most important part if you are trying to follow the sq ft gardening method which doesn't use fertilizer.

Unfortunately in a hot climate this mix will dry out fairly quickly.

Then again in a hot climate pretty much any mix will dry out quickly in a raised bed so I would focus on making at least 25% of the material good compost and the rest should be fairly light, loose, fluffy stuff for best growth.

To deal with the drying out I have found a drip irrigation system with timer to automate it to be ideal.

Drip Works sells laser drilled hoses with an emitter every 6 inches and these work well for raised beds filled with loose soil type material.

For best plant growth you need a medium that is well oxygenated. When you hear about a mix that retains water and is fast draining it is usually (but not always) an oxymoron.

There are not that many materials that drain excess water quickly, but retain ample moisture. The primary reason fast drainage is best for plant health and growth is that the faster the material drains, the faster oxygen is pulled into the mix to fill the spaces in the mix. If the mix drains slowly then the spaces remain filled with water which displaces oxygen. Oxygen is an absolutely critical component to success in the garden and it is perhaps the most often overlooked ingredient to success.

Your best bet is to not skimp on the planting medium. If you do you will pay for it with poorer performance and more rotting issues as well as more disease issues from stressed plants.

An ideal raised bed mix won't contain any soil. Think about it, the reason to grow in raised beds is to get away from the problems associated with growing in the ground (soil). Filling a raised bed with soil is counter productive.

Peat, compost, coir, vermiculite, perlite and similar ingredients are what you want. Yes, they will cost you money up front, but other than the compost which needs to be added to every once in awhile, the other ingredients will last for many years.

Watering issues are easily resolvable with a drip irrigation system. Again, money upfront, but with a raised bed mix that more closely resembles a potting mix than soil and an irigation system you will have healthier, better producing plants, less disease, better yields, less weeds, easier digging, etc.

Going with a non soil mix and drip irrigation means much more time enjoying the garden than maintaining it.

Guy - thanks great info. We will have a drip system and I will look into the vermiculite/perlite/coir and compost. I did buy some steer manure over the weekend and I'm trying to find vermiculite in larger bags than 8 cups which is all Lowes had. I also want to use coir instead of peat moss as I understand peat moss is hydrophobic (not a great choice in the desert i thinking) plus its from endangered peat bogs. I have to get this figured out pretty quick as the beds go in this week!

Peat in the US isn't endangered at all, that is a myth which seems to hold true in European nations. Having said that it *is* more hydrophobic when dry than coir. Where I live coir is 2.5 times pricier than peat though.

With a drip irrigation system though there is really no reason why it would ever dry out to that degree.

For the vermiculite I have never seen it at a department or hardware store in other than tiny, overpriced bags. I got the 4 cubic foot bags from a chain nursery store (Steins). Find a real garden store (rather than a store which seasonally has plants) and they will have it or likely be able and willing to get it.

With a drip irrigation system your choice of materials increases as you really don't need to worry about what the materials do when dry as you can prevent that condition from ever occuring. Focus on light and airy materials and if you wish to not fertilize make sure at least 20% is quality compost. If you pay for it, it isn't quality ;-) Home made or blended from several commercial sources is the way to go.

I suppose being English I grew up hearing about the decimation of Irish peat bogs and have always stayed away from peat.