Community Garden Plot

I've got a 10'x10' plot in a community garden.  For 5 years.  The plot has a water supply and is built on a solid clay soil.  No permanent connection to water supply is allowed.  My plan is to build two 10'x4' raised beds.  Here is my inspiration.

Construction

I plan to use (any available, treated not allowed) 2"x12" lumber for walls - should suffice for 5 years.  Got those corner brackets to hold the walls together.  The bed is dug out so I will probably use a 4" corrugated perforated pipe for drainage.  Irrigation plan does not exist so far but I think about laying a 3/4" PVC pipe on the bottom at least to connect the beds.

Cost: 2x12 lumber (2), 2x6 lumber (1), 3/4" 10' PVC pipe(1), tie-plates, etc - $89.45.

It is much less than pre-manufactured cedar beds, but.. the termites were flying around the lumber as I was building the bed, so I guess it really not going to last.

Soil 

Recommended mix (aka Mel's Mix):

• 1/3 Peat Moss
  From Soil: biodegradable, water retaining additive for soil or potting mix. It is derived from peat formed by decomposed sphagnum moss. The top layer of living sphagnum moss is removed. The underlying sphagnum peat, which is dead material, is then harvested. Colors will progress from light to dark to black as it decomposes. It is acidic with a pH 3.5 to 4, but may be balanced with limestone before being sold to the customer. Repels water if allowed to dry out. Too much peat moss can lead to soil compaction.
• 1/3 Vermiculite
  From Soil: non-degradable, aluminum-iron magnesium silicate. Added to soil or potting mix because of its water retaining properties (220 to 325% by weight). The pH is basically neutral (7.0) but it contains carbonate compounds, which can result in alkaline characteristics. So a typical pH in water can range from 6 to 9. Particles are flaky & can break into smaller pieces if the soil is mixed too much or handled roughly, leading to compaction.
• 1/3 Rich Compost.
  Here are some options (ordered!). Chicken manure?

Alternatively I can buy soil premixed.  Looks cheaper, actually.  Although control over soil content is lost.  Here are some options:

• Kellogg Garden Organics Raised Bed and Potting Mix
  has bad reviews and is cheap.
• Kellogg Garden Organics Patio Plus Premium Outdoor Potting Mix
  sounds like a reasonable compromise.
• Square Foot Gardening Potting Soil Mix
  looks like a winner!  Too bad it is not an option because of high shipping costs.

I will need about 4x10x1 = 40 cubic feet of soil to get things going... Plan to finish the first bed this week.

Decided to go with a custom mix!  Order placed totaling


2 cu. ft. Vermiculite Soil Amendment
Model # 100521092,
Store SKU # 217047,
$20.97,
7,
$146.79
3 cu. ft. Peat Moss,
Model # 3001.CFC003P,
Store SKU # 673166,
$12.97,
5,
$64.85


Total: $230.69

1-cu ft Organic Compost, Item #:49674 Model #: 3207, $2.98, 14, $41.72
Total: $45.37

And this is just one raised bed.  Pretty expensive!

Irrigation

Should I go for PVC piping with manifolds or stick with simple 1/2" drip tubing into 1/4" microtubing, etc?  Mmmm.  We shall see..