Spacing between tunnels depends on local weather context and tunnel orientation. 

Local Weather

Special considerations should be given for rain and snow. Each poses its own unique challenges and require different spacings. 

Rain. Tunnels can create a watershed for neighboring tunnels and crops. Thus causing issues with flooding or seed erosion for direct-seeded crops on outer rows. In general, one's soil drainage may place restrictions on how close. This can be mitigated with a cover crop.

For example, one customer positioned their tunnels with only a twelve-inch walkway between and planted a cover crop. This suppressed weeds and increased water absorption preventing muddy conditions. There was no concern with shadows due to orientation and crop selection. 

Snow. Positioning tunnels too closely in a northern climate creates a natural snow ditch. Additionally, any snow that is removed has nowhere else to go. Depending on snowfall amounts and machinery size, one should count on at least 8-15 feet between tunnels. 

Tunnel Orientation

Spacing between tunnels in relation to the sun is a concern due to shadows cast by the neighboring tunnel. This is more or less important in light of the growing season and crop selection. Ideally, tunnels are in an east to west orientation for solar gain. However, multiple variables must be considered. 

Generally speaking, tunnels should be at least a tunnels height away or 8-10 feet. However, they can be closer.