Scrap wood is certainly fine and it what I use in my garden.

First make sure the box is located where it will get at least 6-8hrs of direct (no shade) sunlight, not daylight but direct sun. If you stand between it and the sun you will see your shadow.

It looks like there may be some things nearby that will block the sun.

< I should get a tomato cage for the tomato plant, right? Do the peppers need anything?>

You can try the cages on the pepper plants, often the soil is too soft to support tomatoes in cages but can work for peppers which won't get as big or heavy.

But for tomatoes I like Upright supports screwed to the side of the bed. I found some links from days gone by but feel free to search for more.

http://forums.gardenweb.com/discussions/2162223/can-tomatoes-and-peas-climb-twine

Vertical Support

Not sure which side is North in your photo but make sure you plant your taller plants (tomatoes) on the North side. This is so the tall plants don't block the sun.

Spacing can be taken from the seed packet - use the seed spacing after thinning since you won't be thinning. Draw it out on paper to see if you will have room for what you have planned.

Keep a Garden Notebook. Each spring review what went well last year and what needs improvement. Winter is a good time to plan the next garden layout, plants, etc.

Start small and try to avoid overcrowding. If you want more plants next year make another box. Cherry tomato plants tend to grow very tall (vines) and will provide lots of tomatoes.

I am so glad you are teaching your son to garden. Kids are like sponges and learn so quickly then will ask you questions you never ever thought of to make you think AND learn.

HTH and good luck.

Any other questions?

Karen, best of luck with your garden box. You can crowd the plants somewhat, but you have to be prepared that some plants will be crowded out and may be stunted. I had a couple of full raised veggie beds, but ended up buying a six-pack of string bean seedlings on a lark. I crammed them in. About half have not prospered, one died due to a lack of water and the other two are doing great. I knew that not all would do well, but I haven't planted them before so I wanted to see how they'd turn out. I like them, so next year I will have to plan better and leave some space for them.

I would definitely get a tomato cage. I like the square folding type as they seem sturdier than the circular cages. As you have your plants close together, you may be able to use the outside of the cage to support one of the pepper plants. Again, you will have some crowding and the veggies may not grow to their full potential, but you will have some nice variety.

Best of luck!

Oh yes, our local nurseries sell lots of strawberries that work well in our zone. I have bunch that I've neglected for years as the snails get all the fruit no matter what I do.

Probably a bit late now but I would go with three peppers in the back, two squares of bush beans and one square of swiss chard in the middle (more on the chard later), and carrots in the front. The tomato can be put in a large-ish container. It'll take up too much space in the bed.

Now, I know you said your son wanted spinach but that is a very fickle plant. Any type of warmth at all and it will bolt (or send up a flower stalk) at which point it'll be done for the season. Swiss chard is a good substitute that handles summer temps better. It does get larger than spinach if you let it so pick the leaves while they're young. Plus it has colorful stems.

You can pretty much disregard the spacings on packets. Check out the FAQ here on square foot plant spacings.

Rodney

Edit: Here's a link to that FAQ I mentioned. http://faq.gardenweb.com/discussions/2766684/what-are-recommended-plant-spacings