Strategies for Seasonal Summer Systems

John Anderson, Hedgerow Farms

Working irrigation canal banks provide an excellent setting for perennial native plants to support a rich, biodiverse system with multiple benefits. Surveys of undamaged banks on vegetated western streams provide living models that healthy irrigation banks decrease erosion and water problems while functioning as efficient water transport systems. The goals of native bank vegetation systems include the following: suppress weed invasion and thus reduce herbicide use; minimize soil erosion, thus reducing maintenance; support water quality as vegetation filters excess nutrients; and simultaneously enhance biological diversity and aesthetics.

If possible, the slope to be planted should be regraded to no steeper than a 3:1 slope to ease planting and maintenance. If the bank can be seeded, the seed bed should be prepared with a harrow or disk prior to planting. A typical canal bank planting involves seeding in the dry zone and upper high moist soil zones and coming in later with plugs to plant the water line and low, moist soil zones.

Weed control is especially challenging on canal banks with constant summer moisture and a regular influx of weed seed from upstream. At least one prior year of complete weed suppression (no seed produced) is recommended before planting a site, and vigilant weed suppression during the first year after planting is crucial for successful establishment.

The list below of recommended plants is intended for consideration and choice, but will not solve all problems: the idea is to initiate innovation and experimentation on specific sites. In fact, there are plant characteristics not included here that may well bear on plant choice: for example, dormancy, soil preference, height or vegetation volume (biomass), root structure, herbicide tolerance, etc. It is important to note that we have had particular success with Creeping wildrye in many canal bank situations. Its tolerance of summer moisture and its rhizomatous growth form provide very effective competition with and suppression of typical weeds.

Four distinct zones have been defined to delineate the planting scheme shown below.

1. Water Line Zone 

This zone is submerged or very wet much of the time during the irrigation season. Here, Cattails (Typha spp.) will try to grow in unmanaged systems. Recent experimentation with Baltic rush offer encouraging results since they withstand fluctuating water levels and go dormant in dry, dewatered conditions. Though Baltic rush forms a dense mat of weed suppressing vegetation, its small vertical growing stems do not significantly obstruct water flow.

2.  Low, Moist Soil Zone

This zone is moist during the irrigation season and would be typical of a wet meadow or perennial stream dry edge. Left unmanaged, this zone becomes inundated with Watergrass, Barnyardgrass, Sprangle top, Jointgrass, nut sedge and other undesirable weeds. Spike rush would extend into this zone.

  3.  High, Moist Soil Zone

Similar to the low zone, but drier, this zone accommodates the following:

4.  Dry Zone 

This zone is dry during the summer. The deep rooted plants in this zone will frequently have access to summer water from the canal especially on better soils and low berms.