Compost in raised beds

The local nursury is selling compost. $23/yard vs $20/yard for loam. Their loam is way to rocky. I am building raised beds. Will a raised bed of compost have enough structure for growing large shrubs? . I know this sounds like a crazy question, but this stuff is so light and fluffy. Really nice though. Thank you.
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g'day jack,
that would be good for raised beds, if i used it i'd probably want to pack it down a littel so it wasn't so loosed.
but ther may be more economical stuff around?
1.. that composted waste they create and refuse/garbage tips etc.,. in lots of places they give that to local people.
2.. mushroom compost straight from the farm, lots of retailers around but if you have a farm within driving distance some often give it away and others have a small charge.
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Jack wrote:

Unless the bed is raised 3-4 feet above the natural grade, you will create problems using only compost. What you should do is dig down inside the bed to a depth of at least 4 feet from the top of the expected planting level. Break up the clods; a four-prong "potato hook" cultivator is excellent for this. Then mix the compost with the native soil, using enough compost so the result comes to the top of the raised bed when packed down firmly. Use a spading fork for mixing. (Don't use a pitchfork, which is likely to break.) While mixing, include some phosphorous (bone meal or superphosphate); phosphorus does not leach through the soil and must be placed where roots will find it.
The result will be a soil mix that does not inhibit shrub roots from growing beyond, into the native soil.
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David E. Ross
Climate: California Mediterranean
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Four feet??!? That's a little over the top. 18" should do.
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Ann, gardening in Zone 6a
South of Boston, Massachusetts
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Ann wrote:

18" might be okay for annuals and perennials. Even then, tomato roots might go 6 feet down in good soil.
For woody shrubs, root might easily grow to a depth equal to the height of top growth.
Note also that I said "from the top of the expected planting level". If the bed is 2 feet above the natural soil, then you have to dig down into the natural soil only 2 feet.
If you have a good mix of compost and natural soil in the RAISED bed that totals 4 feet, then roots are very likely to grow even deeper than the soil was prepared. If you have no mix at all, the roots will be reluctant to grow beyond the compost. Compost by itself is too friable to provide a good anchoring of a shrub.
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Just a followup... . The stuff was just too light. Therefore, I did a mix of about 1/2 soil to 1/2 compost. Probably more soil near the bottom of the hole. That seems to set the plant better. Then I top dressed around the plant with all compost. . Lots of transplants. Lets hope they take. Thanks for your time.

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