Greenhouse Growing

Here is a list of the largest vegetables that will need the most
spacing in your greenhouse:
1 bush type beans: minimum of five feet between rows,
2 cabbage: a foot between rows,
3 peppers: about a foot between rows,
4 cantaloupes: two to three feet between rows,
5 squash: two to three feet between rows,
6 tomatoes and watermelons: minimum of two feet between
rows.
All other vegetables (beets, carrots, garlic, lettuce, onions,
peas, radishes, spinach, and turnips): five to ten inches to grow
fully in the bed in your greenhouse.
For carrots, beets, and onions that grow deep down in the dirt,
keep your soil at least two foot deep as the roots on some of
these plants and the vegetable that grows from these plants
can get to be very large under the soil.
Mixing vegetables in rows is a good idea. Plants that are different
put side by side will not compete for the nutrients, soil and water.
For example, take onions and lettuce. One grows down in the dirt
while the other grows up from the soil – they grow well side by side.
However if you were to put onions and carrots together, they will be
competing for the soil space.34