Hello Kathleen,

Thank you for contacting the Denton County Master Gardener Help Desk.

Drainage question:

Should I:

1) relocate the bed to a place with better drainage - this would be the side of the house visible from the street. Not as convenient for watering.

Full sun is REQUIRED to have a great garden.  They just don't have varieties that do well in shade.  Having said that, tomato production may be extended a week or so with shade cloth when the days are long.  

There are several ways to address the raised bed drainage without having to alter the landscape drainage unless there is ponding of the water several inches deep.  Half inch holes at the bottom of the side boards should allow any standing water in the bed to drain.  The spacing is not that critical. I drilled mine every 2-3 feet as close to the bottom as I could get them with out the edge of the board failing.  While it is important for the bed to maintain some moisture, plant's roots also must have air for proper functioning.  Recommended soil is 50% solids, 25% water, and 25% air by volume for happy plants.

2) build the bed higher (add another level of 2x10s).

The TAMU Extension Agents recommend 18 to 24 inch depth, so you will likely get better results adding another layer.  As 

3) address the drainage issue - what kind of company would I look for to help identify and address this? (after I check for water leaks in the sprinkler system, that is).

Most of the sprinkler companies also do landscape drainage, there are contractors that just do landscape drainage, and most landscape design companies have drainage experts on staff.

The design and construction is not complicated and YouTube has videos on installing French Drains.  All the parts are available at the local home improvement stores.  Under ground sprinkler lines, electrical wires, phone/cable lines, and gas lines may complicate the issue for a DIYer.

Soil prepping questions:
1) If I leave the bed it's current size, should I simply add 2-3 inches of compost and granular fertilizer (per package instructions)? Should I add some perlite or sand for drainage?

One of the major advantages that a raised bed or container garden offers over an in ground garden is the ability to easily alter the drainage characteristics.  Mud and clay mud can make the water pond for a considerable length of time and sand will allow it ALL to drain out too quickly.  This time of the year, the soil should stay moist 2-3 days while not being soggy for more than 5-10 minutes after being drenched to saturation.  I usually have issues with organics from prior year decomposing and retaining too much water.  Like you said, sand and perlite will solve the problem, but I've also used the shredded bark mulch and wheat straw.  That is because I'm cheap. A bale of wheat straw and 2 cu ft of mulch are less than $10 each, not that it is the best or recommended approach.

2) If I increase the height of the bed, so I mix in a new ratio of 1/3 compost (or peat moss?), 1/3 topsoil, 1/3 perlite or sand?

I'm not sure if you are buying your Dyno Dirt in bags or bulk.  At the bulk pickup place, they also have several different flavors as do most of the other places that sell compost. What I like about the bulk places is that you can see the mix and at some, run your hand through it and get a very goo idea of the textures and composition.  Many nurseries also sell in bulk as they also use the mix for their potting and containers.

3) In my containers, should I amend the soil (and with what?) or should I toss and start over each year?

I've never seen a mixture that couldn't easily be improved without starting over.  The one exception would be if it was heavily infected with nut grass/nut sedge or dew berry briars or other problem plant that couldn't be solved by pulling them out.  A soil test is the wisest approach to see what needs to be done for nutrients.  The TAMU Extension offices recommend using the TAMU soil test lab.  I sent them my samples last year about this time on a Sunday, they arrived on Wed, and the Lab emailed me my results on Thursday.  Use the "Urban Soil Test Form" on their website for selecting the tests to run (Basic + micro nutrients) is probably more than you will need.  The form allows for selecting what you want to grow and their recommendations will be tailored for those plants.  In my case, I found my soil had almost toxic levels of phosphorus, and adding any more using one of the "complete" fertilizers would have actually damaged my garden.  With all the effort that goes into our gardens, it just doesn't seem wise to "guess and hope" when it is an issue easy to accurately control.

RESOURCES:

TAMU Soil Testing Link:

http://soiltesting.tamu.edu/

Our website info on raised beds (contains additional links)

https://dcmga.com/the-dig-raised-beds/

If you have any other questions please contact us again.

Edsel