Building Good Soil For Raised Beds

Hello All. I am completely new to AZ gardening and plan to start some raised beds in the yard of the home I am renting soon. I was given some hints about having to "build" a more suitable, water-holding soil here for the garden to thrive but all I can remember is the advice to mix in coir (coconut husk fiber) with the soil.

I have, luckily, some compost that will be ready to use when I build the beds, which so far I am planning in a full-sun patch of the yard because that spot is convenient. I am assuming I will need some shade over the garden too...Anyhow. I am interested in any hints to build a suitable soil for this garden!  This will be a vegetable/ herb garden.

Thanks! - Rachel

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  • You should have good results using about half native soil mixed with your compost and other organic matter. The native soil probably needs only nitrogen. I add composted manure every season, and that seems to continually improve the soil. You probably won't have "perfect soil" at first until the microbes increase their work, but this will put you on the right path.

  • Seems this came down to a raised verse sunken bed question.  I personally will start with a raised bed in part because I don't know exactly where I want to place my beds yet but want to get something started this season.  Also the house I'm in is some 40 years old and I have no idea what the previous residents put in the ground ( I did see from previous google street view pictures that it looked like they were doing some kind of AC repair in the back yard)

    I also want to experiment with a raise verse sunken bed.

    So back to the original question Rachel raised.  What kind of soil amendments\additions would you recommend?  I'm planning on building soil for my beds using compost, coconut coir,azomite, and worm castings.

  • Hey Rachel,

    I had a similar issue, but with rocks in place of the grass. Here are some links to the off-ground bed I built with pallets and fence slats - the whole thing cost me about $50 to build. It's 12' x 3' x 2.5' and filled to 18" deep. I do have to water it daily in the summer and feed it more frequently, but it is otherwise fantastic for my needs! If I were building on top of bermuda grass, I'd stack the foundation 2 pallets high instead of just one, or I'd place some black weed sheet down beneath the pallets. Feel free to pick my brain if you want to bounce more ideas around. 

    http://www.pinterest.com/pin/272116002459533901/

    http://www.pinterest.com/pin/272116002459533494/

    http://www.pinterest.com/pin/272116002459533521/

    http://www.pinterest.com/pin/272116002459533584/

  • The best way to garden here is directly in the ground, not raised beds, unless you are in a really rocky area up on the mountain. Sunken beds hold moisture better in our climate, and all that is really needed is adding organic matter, 50% compost to 50% native soil. You will always need to continually add more organic matter as you go. 

    So, unless you have a really rocky area go in the ground an you will have better success, less inputs like water (raised beds dry out fast and gravity pushes the water below the roots in a raised bed), and less work, and less costs.

    Also, our seasons are different than most of the country. Check out the Master Gardener planting guide here:

    http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs...

    Phoenix area is about 1,000 ft above sea level.

    Hope this helps

    • Thanks for that Ericka, and the link. On that note...the entire yard is covered in very vigorous Bermuda Grass. So, I was initially thinking to dig it out but was told that this is nearly impossible. I really don't want to use chemicals to clear the grass in this area, so any ideas on this would be appreciated as well.

      Will check out link tomorrow!

      Rachel

    • Rachel I echo what Ericka says about in-ground vs. raised bed.  If you are thinking that a raised bed will avoid the bermuda you may not be that successful.  Unless you put a solid bottom on the bed (using concrete) the bermuda would find its way into the bed.  If you really want a bermuda-proof raised bed you would need to be a solid container on legs with drain holes and it would need to be 18 inches deep and at least 2 feet wide by at least 2 feet long.  This would give you the year-round growing possibilities we enjoy here.

      The depth of the bed would keep the soil moister, longer.  The sides of any raised bed whether sitting on the ground, on legs or in large pots will heat up substantially in the summer, so planting "IN" 6 inches from the sides is my recommendation.

      You would still need to build a soil mix and it should include some of your native soil for the microbs.

      Back to getting rid of bermuda without chemicals.  You have to dig it up, going down at least 2 feet to try to get the roots and stolens.  You have to sift the remaining soil and then you have to be diligent in keeping the grass our of the beds.  If you have ANY bermuda within many, many feet of the in-ground, or touching ground bed, the grass will eventually send runners out and you have to be diligent about that also.

      So building a legged raised bed takes work - but theortically you can take it with you when you move (since you are renting) vs. digging the bermuda out.

      You will have to figure out what will work for you.  Several largish legged containers butted up against each other will give you the 'density' you may be looking for to have a year-round flourishing garden.

      Hope these ideas help.  Good luck.  Don't give up :-)

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