Season Extension Tunnels.

'Shoulder season extension tunnels for regenerative soil systems.'

(Portable hothouses, Caterpiller tunnels, Season extension tunnels)

Caterpiller Tunnels as they are often referred have been around for a few decades, finding a place in the fringes of small growers systems in varying forms of DYI or more often than not, clumsy kit forms. This earlier tangent has completely shifted to the very real need of professional micro-farmers.

More recently the groundswell in regenerative, soil focused micro-farming has led to rethinking the need for good quality, professional use Caterpiller Tunnels that are economically justifiable.

Crop rotation is of critical importance for succesfully regenerating living soil, by using a modular/standardised bed block system we can incorporate standardised season extension tunnels into the design. This allows a number of benefits to the regenerative farmer.

  • Timed cover of crop/bed block for effective season extension.
  • Timed removal of early season cover.
  • Inpermanence of hothouse soil use.
  • Greater versilitility in planning
  • Seasonal adaptibility.

Typical design.

  • Span,the Caterpiller Tunnel kits from Farmers Friend span four permabeds, about 5metres.
  • Height, the eight metre arcs of one inch (25mm) tube steel peak at 2.3m and is semi circular in gradient.
  • Length between end hoops, although lengths could easily be modified Farmers Friend's Caterpiller Tunnels are either 15 metres (50 foot) or 30 metres.
  • End 'triangular tie off' lengths, these can be modified slightly and range from 3 to 4 metres from the last hoop to a star picket, angled backward and centred perpendicular to the end hoop.
  • The beds need spare area at the bed ends ranging totalling 6 to 8 metres overall, this can be dealt with by losing a bit of end bed whie still growing within the tapered area.
  • Side walls, typically these can be lifted and will allow good air flow across both lengthways.
  • Semipermanent stays, the hoops sit over rebar inserted about 400 mm into the earth. A 'Jack Jaw' star picket remover will make easy removal of these, or a refashioned diamond jack.
  • Centre perlin, in the basic and effectice form the perlin is a nylon strap, tied off to the star pickets at either end. Snow protection can be added by using the static tube steel perlin option.


There is a variety of Caterpillar Tunnel options available from making your own from sourced components to buying a kit.

Pros and cons.

  • If not set up correctly they will be problematic.
  • Can be set up quickly by few people on a still day
  • Australian sourced hothouse film is more expensive than the foreign film of the same quality in the US kits.
  • Although sourcing your own may save you dollars, it may take a whole lot more time and headspace away from the matter at hand, growing and selling the food.
  • It may be possible to hybridise the imported kit elements with the some easily sourced affordable parts such as rope, caribeners, perlin strap, 150um film, rebar, again you will need to cut a bunch to length of about 800mm.