I would use graph paper or poster board. Are there paths already around your 4x24 plot?

I do use graph paper. I use 4x4 Quad ruled (4 squares to the inch) and map out the entire space.

If, for instance you make each square of the graph paper represent 1 foot of garden space, then draw a box that is 4 squares wide by 24 squares long. Then draw circles inside the box to represent the plants. For tomatoes I give at least three feet for each plant. For other plants use the spacing suggested on the back of the seed packet or borrow a copy of Square Foot Gardening, which has a very good spacing plan for many common vegetables.

Figure out which direction your garden plot faces and put the tomatoes (and other tall plants) on the northern end and the smallest plants on the southern end.

Also, you can grow determinate varieties of tomato, which take up less space and don't get nearly as tall.

I found a great Garden Planner on Mother Earth News website. They offer a 30 day trial FREE, you don't have to provide a cc#, just register. Check it out.

http://www.motherearthnews.com/garden-planner/vegetable-garden-planner.aspx

With the advent and ease of digital cameras, a couple of times a year, I take photographs and print them. Black an white is usually better for what I do. Then I mark up the photograph with notes for next year.

Simplest thing is to use your word processor. Just create a table with squares of equal size (I use 1/2") each representing a square foot. The you can draw circles to represent plant positions or different background colors for entire rows. I also use different font colors to represent early crops that will be replaced by later crops. Works pretty well for me.

The info above is excellent. I use graph paper, too. FYI, most planners recommend that you orient your rows north to south so that all plants get maximum sun.

Also, if you store your leftover seed in ziploc bags in the refrigerator, you can use it for two, maybe even 3 or 4 years more. If my seed is more than two years old, I sow more heavily in order to get a good stand. Still, it's better than wasting seed altogether.

I would just point out that if your plot is four feet wide AND has an adequate path around it, you can plant the entire 24'x4' area solidly with plants (a la Square Foot Gardening). By standing in the path, you should be able to reach into the center of the bed without needing to step among your plants, thus eliminating the need for rows. (Seed packets might say plant seeds four inches apart in rows two feet apart. You can ignore the two feet apart if you don't have to walk among the plants.)

If you have good soil and are feeding no more than four people, and not planning to can, etc., 3 or 4 tomato plants are probably all you will need. If you cage them, you can plant them 2 feet apart. So a 4'x4' square on the north end will accomodate your tomatoes and you still have 20x4' left for other things.

Tomatoes must be rotated every year, so next year you get back to the shading problem. You might want to consider growing your tomatoes in pots so that you can change out the potting mix every year. This, of course, would free up sixteen more square feet for other things.

Gardeners Supply has a garden planning tool on their website that you can use for free too. I enclose a link. (I don't work for them. I just buy from them.)

Here is a link that might be useful: Garden Planner

Sorry, I should add that I am not affiliated in any way with Mother Earth News or their website. I just thought it was a handy tool.

Thanks for all the great ideas! And yes, the paths are already there. :-)

I used Open Office Draw. It's free, open source, and it works pretty well.

Here is a link that might be useful: open office draw