Harvesting Plant Cuttings for Soil Bioengineering

How and when to harvest willow, cottonwood, and red-osier dogwood cuttings for soil bioengineering in BC, timing, species selection, cutting standards, storage, and handling to maximize viability.

Getting the cuttings right is half the job. The most carefully installed wattle fence or live stake program will underperform if the plant material was harvested at the wrong time, handled carelessly, or stored improperly. This guide explains the standards that experienced bioengineers follow.

Soil bioengineering techniques, live staking, wattle fencing, brush layers, live pole drains, gravel bar staking, all depend on the ability of dormant cuttings to root successfully after installation. A cutting that roots reliably becomes a living plant that anchors the slope and initiates ecological recovery. A cutting that fails to root is an expensive piece of dead wood.

The difference between a cutting that roots and one that does not is largely determined before it ever reaches the site: when it was harvested, how it was handled, and how it was stored.

Cuttings must be harvested during the dormant season: the period after the plant has shed its leaves and before it breaks bud in spring. For BC coastal sites, this runs roughly from late October through early April, though specific timing varies with elevation and local conditions. Interior and northern BC sites may offer a somewhat shorter window due to later leaf drop and earlier bud break.

The key principle: the cambium layer just beneath the bark must be alive and viable, but the plant should not yet be drawing on stored carbohydrate reserves for new growth. Cuttings harvested after bud break are dramatically less likely to root successfully, the plant has already committed its stored energy to leaf-out, and a cutting taken at that point has little reserve left to initiate roots.

Do not harvest after bud break. This is the most common harvesting mistake.

For BC, the practical harvest window is:

On sites where both harvesting and installation occur in the same season, the dormant season installation window aligns with the harvest window, this is by design.

The four species most commonly used in BC soil bioengineering, in rough order of versatility:

The primary bioengineering species across BC. Multiple species are suitable, each with different site preferences:

• Scouler's willow (Salix scouleriana): Most versatile. Tolerates a wide range of moisture conditions from moist to moderately dry. Common on coastal and interior sites. Strong rooter.
• Hooker's willow (Salix hookeriana): Coastal species. Excellent for wet, riparian, and marine-influenced sites. Very vigorous.
• Sitka willow (Salix sitchensis): Coastal and riparian. Tolerates flooding and saturated soils well.
• Whiplash willow (Salix lucida ssp. lasiandra): River bars and moist streambanks throughout BC. Produces long, flexible stems useful for horizontal material in wattle fences.
• Drummond's willow (Salix drummondiana): Interior BC montane sites. More drought-tolerant than most species; good for drier interior slopes.

For wattle fencing in particular, long stem length and flexibility are the most important qualities. Collect long stems to lay horizontally behind the vertical posts. Keep every stem on the uphill side, then backfill and lightly tamp down the soil.

Black cottonwood (P. balsamifera ssp. trichocarpa) is the primary species on BC coastal and interior riparian sites. Balsam poplar is more common in northern interior BC. Both root readily from large-diameter cuttings (poles) and are excellent for pole drain applications and larger structural elements.

Cottonwood is less tolerant of standing water than willow but thrives on moist alluvial soils adjacent to streams. It grows rapidly, faster than willow in the first few years, and contributes quickly to riparian canopy closure.

A native shrub of riparian zones throughout BC. Less commonly used than willow or cottonwood, but valuable on sites where dogwood is a natural part of the understory community. Red-osier dogwood cuttings root readily and the established plant is highly palatable to ungulates, avoid using it on sites with heavy deer or elk pressure unless protection is provided.

Alders do not root from cuttings the way willows and cottonwood do, they must be established from seed or container stock. However, they are important species for site preparation and nitrogen fixation on reclamation sites, and they self-seed readily onto disturbed ground where conditions are favorable.

The minimum acceptable cutting diameter at the tip end is 2.5 cm (roughly the diameter of a thumb). Cuttings thinner than this do not have sufficient carbohydrate reserves to reliably initiate roots before desiccating. Larger is generally better, a 4–5 cm diameter cutting has substantially more reserve energy than a pencil-thin twig.

Horizontal wattle material can be thinner where flexibility is needed, but these are still living cuttings. Moisture contact and viable material matter if they are to establish.

For live pole drains, cuttings should be at minimum 2.5 cm diameter at tip but ideally 3–5 cm diameter and as long as practical, poles 1–2 m long provide the greatest drainage effect and the largest root-initiating surface area. Small-diameter twigs (pencil-sized) are retained in pole drain bundles specifically to provide root surface area in the upper portion of the trench where capillary moisture may be limited.

• Live stakes: 40 cm minimum; 60–80 cm preferred. The cutting must reach the capillary fringe above the water table when installed. On deep, well-drained substrates, longer stakes (1 m+) may be necessary.
• Wattle fence vertical stakes: 1.0–1.5 m. Must be driven deeply enough (0.75–1.0 m) to reach soil moisture.
• Wattle fence horizontal stems: Use long stems laid along the fence line behind all of the vertical posts. Backfill and lightly tamp down the soil as the fence is built.
• Live pole drain poles: 1–2 m. The full length is buried in the drainage trench.
• Modified brush layers: 60 cm minimum; 1–2 m preferred. The tip ends must reach soil moisture when the cutting is laid horizontally across the slope.

The period between harvest and installation is the most vulnerable period for cuttings. Three enemies: desiccation, heating, and physical damage to the cambium.

Desiccation is the biggest risk. Cut ends exposed to air will begin drying within hours. Best practice:

Heating kills cuttings. A pile of fresh green cuttings in a warm environment will heat from biological activity within a day or two. Keep bundles loose, shaded, and cool.

Cambium damage from crushing, rough handling, or bark stripping reduces rooting success. Handle cuttings carefully and do not stack heavy loads on fresh material.

In Living on the Edge, printed page 35, David Polster describes soaking for around ten days, citing Schaff and colleagues (2002). He also notes that fully hydrated material may not need soaking, and that roots formed during extended soaking are fragile during handling.

Practical soaking protocol:

On field projects where soaking tanks are not practical, cuttings can be heeled into saturated soil or submerged in a clean stream reach for the pre-installation period.

Where installation is planned for several weeks or months after harvest, cuttings can be held in cold storage:

Snow bank storage is a traditional and effective technique in areas with reliable snowfall. Cuttings buried in a snow bank maintain consistent cold temperatures and high humidity, conditions that preserve carbohydrate reserves without triggering growth. This technique has been used successfully in northern BC and interior sites where adequate snow is available.

Check stored material for hydration and viability before installation. Rehydrate where needed, while avoiding fragile root growth that insertion will damage.

Remove all lateral branches from cuttings to be used as vertical stakes, side branches increase transpiration and reduce rooting success. A smooth cutting drives more easily and loses less moisture.

For horizontal wattle material: light lateral twigs can be left on the stems. Lay all material behind the vertical posts before backfilling and lightly tamping down the soil.

For live pole drains: small-diameter twigs (pencil-sized, approximately 5–10 mm) from the lateral growth are retained in the bundle, these thin-diameter rooters provide rooting surface area in the upper, drier portions of the trench where the larger poles may not root as readily.

Cut at nodes when possible, willow and cottonwood root most readily from nodes where the vascular tissue is concentrated.

Identify the willow species and check whether the source and treatment conditions fit. Willows are useful cutting material, but a nearby stand is not a substitute for site assessment.

Successful soil bioengineering depends on getting every step right, from species selection and harvest timing through installation and establishment. Polster Environmental advises on the full implementation sequence, including harvesting protocols specific to your site and region.

Polster Environmental Services, soil bioengineering for slope stabilization and ecological restoration across British Columbia.

Every living technique starts with good cuttings, and getting them right is half the job. These are the field practices David Polster refined over four decades of collecting willow and cottonwood across British Columbia, from finding the right material to getting it ready to root.

Cuttings collection is about a third of the labour on a soil bioengineering project, so the collection site matters. David Polster looked for places where pioneering willows and cottonwood had been cut back and resprouted into straight, uniform stems: highway edges, abandoned rail lines, and powerline rights-of-way. Uniform straight material makes every structure that follows faster to build.

Straight, even stems are the goal; different techniques need different material.

The right hand tools make collection efficient and safe. David's go-to was the Silky Zubat hand saw: one saw can keep three or four people busy trimming and cuts nearly as fast as a chainsaw, without the protective gear a chainsaw demands. Felco #2 pruners handle the fine trimming and Bahco loppers take the heavier stems.

Trim side branches close to the stem; work from the butt toward the tip.

Bundling cuttings in tens makes them easy to carry and to count. Before installation, soak the cuttings in clean water for up to ten days so they are fully hydrated and ready to root. Cuttings that go in dry, or after bud break, are the most common reason a planting fails.

• Polster, D.F. 2021. Living on the Edge: A Manual for the Restoration of Drastically Disturbed Sites. Polster Environmental Services Ltd. (basis of the PES online course).
• Polster, D.F. 2006. Soil Bioengineering for Riparian Restoration. Canadian Land Reclamation Association Conference, Ottawa, ON.

The first harvesting section covers the workflow. These extra field details show the decisions that keep material viable: choose the right donor stand, trim cleanly, and sort out weak stems before they reach the installation site.

Collection sites are chosen for form as much as species. Repeated disturbance along rail corridors and access edges often produces straight, even willow and cottonwood stems that are faster to harvest and easier to install.

Powerline rights of way can be useful dormant-season donor sites.

Clean trimming reduces snagging and makes bundles easier to handle. The living bark and cambium are still protected, but side branches are removed close enough that the cutting can be installed without tearing or hanging up.

Cut above a fork once the stem is below useful diameter.

• Source deck: David Polster, Cuttings Collection.
• Polster, D.F. 2021. Living on the Edge: A Manual for the Restoration of Drastically Disturbed Sites.

The success of any soil bioengineering installation depends on the quality of the cuttings used. Cuttings must be dormant, fresh, of the right size, and from suitable source plants. Poor harvesting practice, collecting too late, using the wrong species, or allowing cuttings to dry out, is the single most common cause of bioengineering failure that has nothing to do with site conditions. Cutting collection is a skilled field task that requires understanding of dormancy timing, species identification, and proper handling protocols.

Step-by-step procedure:

1. Time your harvest correctly: collect cuttings during dormancy: late fall (after leaf drop) through late winter/very early spring (before budbreak). The ideal window is the period of maximum dormancy in mid-winter. Never collect after buds have significantly swollen or leaves have begun to emerge.
2. Identify suitable species: willows (Salix spp.), cottonwood/balsam poplar (Populus spp.), and red-osier dogwood (Cornus stolonifera) are the primary cutting species. Collect from local sources growing in conditions similar to the restoration site, use gravel-bar willows for gravel bar staking, riparian willows for bank protection.
3. Select healthy source plants: harvest from vigorous, healthy plants showing no signs of disease or insect damage. Previous-year growth (long, straight shoots from the current season's growth) root most reliably.
4. Cut at appropriate diameter: for most applications (wattle fences, live staking, bank protection), cuttings 1–3 cm diameter root well. For live palisades, minimum 4 cm at the tip is required. Avoid very thin cuttings (less than 0.5 cm) which dry out too quickly.
5. Bundle and keep moist immediately: bundle cuttings loosely and wrap in damp burlap or moist newspaper immediately after cutting. Keep out of direct sun and wind. Never allow cuttings to dry before installation.
6. Use within 3–5 days of harvest: fresh cuttings root dramatically better than stored ones. If storage is unavoidable, keep bundles in a cool, shaded, moist environment (not submerged, they need air). Do not store in warm conditions.

Common failure modes:

• Collecting after budbreak, cuttings fail at high rates; shoots emerge before roots
• Using inappropriate species, upland species fail in riparian applications and vice versa
• Allowing cuttings to dry, viability drops sharply within hours on warm, sunny days
• Cuttings from unhealthy or diseased source plants, poor rooting, disease spread
• Harvesting from distant populations, local genotypes are adapted to local conditions

Rooting depends on viable material, temperature and sustained moisture. Stored reserves support early growth, but they do not vanish at bud break and rooting cannot be assigned a universal number of hours after planting.

Local provenance, collecting cuttings from plants growing in conditions similar to the restoration site, has been shown to significantly improve establishment success compared to using material from different climatic or hydrologic settings. Polster (2008) emphasizes local collection as standard practice in BC bioengineering, both for establishment performance and for maintaining local genetic diversity in the restored vegetation community.

Sources: Polster, D.F. (2008). Soil Bioengineering Systems for Slope Stabilization and Reclamation. Polster Environmental Services, Victoria, BC. | Allen, H.H. & Leech, J.R. (1997). Bioengineering for Streambank Erosion Control; Report 1, Guidelines. U.S. Army Engineer Waterways Experiment Station, Technical Report EL-97-8.

The Rough and Loose and Live Staking in the Field project documentation covers the full workflow from harvesting to installation, a useful field reference for crews learning the dormant-season cutting sequence for the first time.

We can review the conditions on the ground and recommend the right living system, sequence, or combination of techniques.