You may wish to change the crops. The four chosen are very easy to grow. Each has different temperature requirements to reach harvest. Corn needs the hottest weather. Cilantro and radishes will grow in cooler weather.
Tomatoes are difficult to grow from seed.
This is a good opportunity to discuss New World food contributions. Set up the stick for altitude angle permanently in a location not impeded by shade, preferably in the garden itself. Teach students how to calculate the angle in the classroom. They can use a scientific calculator or a tangent table. If you do not want to mention trigonometry, they can compare shadow lengths.