Yes, plant growth will be different due to differences in sun interception and even slight temperature variations with height.

Here's some quick math you can do. Take the height between shelves and divide by half the width of the shelf to get a ratio. Go to google and plug in the ratio preceded by the query function "arctan". Google calculates it for you. Take the number they generate and multiply by 57.3. This gives you the minimum sun angle (in degrees) at noon to reach the back of the shelf, any shelf (except the top one). To figure out what it would be for any other position on the shelf, adjust shelf width accordingly in the calculation.

Now, google the NOAA solar position calculator. Plug in your latitude and longitude (e.g. Charleston is about 38 N and 81 W), any date and any time and it will tell you the expected sun angle at that particular time. This should give you a good idea of what to expect.

Correction: I actually mean "maximum" sun angle!

Wow...interesting Dr...never thought about it that way. We just move plants around until we find a spot they like.

We use light colored mesh plastic shelves and tend to use the top shelves the most. We also leave floor space for larger plants. We find some plants do prefer the middle shelves and some even the bottom shelf, but keep in mind there is even considerable variation of sun even on the same shelf. Bottom shelf closest to the glass is very different that bottom shelf closest to the aisle.

There are also step down shelves that have three levels and are shaped like steps so they all get decent sun exposure. We opted away from these becaus ethey take up more space and the top shelves are smaller.

Experiment before you build or buy the final shelves.

What a cool greenhouse! After you've done all of the calculations recommended by the DrH you may still find that some of your plants may not get enough light to thrive. Your shelving would lend itself very well to hanging grow lights above the plants on lower shelves.

Using small chains to hang the lights allows you to raise or lower the lights as plants grow. If you use a power strip to connect the lights to a power source, you can also use a timer to turn them all on and off at specific times so that your plants get the required amount of light for optimum growth.

Having enough light and the right kind of light can prevent a whole lot of other problems with young seedlings. For example, if the light is too thin seedlings get leggy, fall over and rot. Keeping the grow lights just above the grwoing seedlings top set of leaves encourages sturdier stems because they don't have to "reach" for the light. Healthier plants are more resistant to insect damage and diseases too.

Cheryl