Stem Cuttings

Some deciduous woody plant species rapidly form adventitious roots from stems and can be easily propagated in the field with dormant stem cuttings stuck in moist soil. Field propagation of cuttings can reduce or eliminate costs, both for materials and labor, allowing increased planting density and volunteer-based restoration without a cash budget. Cuttings can be planted in environments where potted stock cannot. Pacific Northwest indigenous species have been poorly studied and limited research is available to guide harvest, storage and installation methods.

Context

Stem cuttings are an inexpensive approach to plant propagation and can be an integral part of an erosion control plan. Dense cutting plantings can be useful for weed control by providing rapid competition for light and are a valuable resource to support cash poor volunteer-based projects. Cuttings provide a low cost option for adaptive management intervention. Hydrology and soil structure along the wetland to upland gradient may strongly impact a cuttings ability to form roots in the field. Several hardwood trees, rhizomatous shrubs, and tree-like shrubs associated with riverine and wetland environments are viable for cutting propagation. Some species may require wildlife protection as deer and beaver browse can damage cutting plantings. Large cuttings have been used as an anchoring method in large woody debris placement.

1. Selecting Species 2. Harvest, Storage and Pretreatment 3. Site Selection and Planting Methods 4. Revegetation Strategies and Maintenance

Selecting Species

Adventitous root formation is an adaptation to alluvial disturbance where new roots form from stem tissue in response to environmental conditions (Gill 1975; Krasny et al. 1988). Many native species have demonstrated the ability to establish when planted as dormant stem cuttings, but success is species specific and dependant on environmental conditions (Cereghino 2004; Darris 2002a; Flessner 1997; Stannard & Guenther 1999). Many more experimental stake plantings have been completed by regional practitioners but are poorly documented. The following list is a tentative list of species with sources of additional information listed for each species:

Plants commonly used in restoration projects: Corunus sericea (Cereghino 2004), Populus trichocarpa (Stannard & Guenther 1999), Salix hookeriana, Salix lucida (Stannard & Guenther 1999), Salix scouleriana (Edson et al. 1995), Salix sitchensis

Paul Cereghino – 22 Jan 2006 Page 1 of 7 Plants with multiple or well documented reports of success but limited use: Lonicera involucrata (Darris 2002a), Physocarpus capitatus (Darris 2002a; Darris 2002b), Spiraea douglasii (Darris 2002a, Hennelly 1994, Stamphli 1992), Symphoricarpos albus (Cereghino 2004; Darris 2002a; Darris 2002b), Philadelphus lewesii (Darris 2002a)

Plants with poorly documented reports of success, or success under specific conditions: Malus fusca, Oemleria cerasiformis (Darris 2002a), Ribes sanguineum, Rosa gymnocarpa, Rosa nutkana, Rubus spectabilis (Cereghino 2004; Darris 2002a; Darris 2002b), Sambucus racemosa

Plants that can be propagated by cuttings with an unknown ability to establish in the field: Oplopanax horridus, Ribes bracteosum, Ribes divaricatum, Ribes lacustre, Ribes laxiflorum, Rosa pisocarpa, Rubus leucodermis, Rubus parviflorus, Rubus ursinus, Vibernum edule

Where species do not root as readily as willow, pretreatment and proper timing may be critical to success. Some species, like red elderberry (Sambucus racemosa) and indian plum (Oemleria cerasiformis), break bud extremely early in the growing season. Stewards testing these species should plant early, well before bud break. Species with a pithy core, like salmonberry (Rubus spectabilis) (which also roots poorly from older wood) and red elderberry, may loose moisture quickly and may benefit from horizontal planting as a fascine or with stems buried under mulch (Darris 2002b). In general, easy-to-root species tend to do well regardless of the subtleties of method, while the full palette of species may only be available to those willing to experiment and learn the needs of each species.

Cutting propagation is cloning and revegetation with limited genetic variation may produce plant populations that are less able to adapt to disease or changing environmental conditions. A species may develop local genetic populations that are adapted to local conditions and the environment of the parent material and the conditions on the site may have an influence. The genetic patterns of native plant populations have not been studied, and so actual affects are un-documented.

Harvest, Storage and Pre-treatment

When a stem is cut it begins to die. It must form roots before it dries out or rots. Maintaining stake moisture levels is the critical objective that drives the majority of harvest, storage and pre-treatment procedures.

Stakes can be obtained from donor plants on site, power line rights-of-way, salvage sites, infrequently cut roadsides, infrequently mowed stormwater detention ponds, old pastures, or any other site where native woody plant growth is present but unwanted. A number of contractors working independently, or through retail or wholesale native plant nurseries, will provide pre-cut stem materials for 25-40 cents a foot.

Harvest may degrade the donor plants by spreading disease or by creating an opportunity for competing vegetation. Suggestions for reducing impacts on donor plants include: reducing the number of stems cut per plant, leaving over 8 inches of stump on cut stems, and cleaning pruning tools between plants. Wild cutting should be limited to sites where there would no consequence from degradation of parent material. No agricultural production of indigenous cuttings has developed in our region, although agricultural cutting blocks are part of the Poplar forestry industry.

Flooding can stimulate adventitious rooting (Gill 1975; Krasny et al. 1988). No tests have been conducted to determine if stakes taken from plants under inundated soil conditions have a higher rooting ability than cuttings from plants in drier soils. Variation in rooting ability between populations within a species has been documented (Puri & Swamy 1999), but differences in rooting ability among indigenous northwest species populations has not been studied.

Larger cutting diameter has not been clearly shown to improve rooting ability in all species (Cereghino 2004). As long as rooting ability is sufficient, larger stems may provide some value in their ability to survive installation, and resist desiccation. Pole cuttings using tree trunks have been successful established for willow (Salix spp.) and black cottonwood (Populus trichocarpa)(Bentrup & Hoag 1998). Stem age may strongly control rooting ability, with younger stems rooting more successfully than older stems among species sensitive to stem age (Darris 2002a).

Paul Cereghino – 22 Jan 2006 Page 2 of 7 Adventitious roots that form at nodes may constitute a significant portion of the rooting ability of some species. Higher nodal density may increase the number of roots formed in the rooting zone, thus increasing survival and growth. red-twig dogwood (Cornus sericea) has had high mortality on stakes with only one or two sets of buds (Cereghino 2004).

Some suggest transporting whole branches to reduce water loss (King County 2004; Schiechtl & Stern 1996) while other process cuttings in the field for easy transport (Cereghino 2004). No controlled comparisons have been documented.

Numerous studies suggest that there is no loss of rooting ability after storage as long as the stakes remain dormant and moisture levels are maintained. Stakes have been wrapped in plastic and refrigerated, or buried in moist sawdust or snow with success. (Bentrup & Hoag 1998; Fischenich 2001; Schiechtl & Stern 1996). Both near- freezing and below-freezing storage have been successful for Populus (Cram & Lindquist 1982; Chmelar 1974; Hoag & Short 1992; Phipps & Netzer 1981). Below freezing storage may require transitional storage for 2-3 weeks at 41 degrees F to provide time for buds to emerge from dormancy (King County 1993). Storage under cool moist conditions may improve rooting ability in some species by allowing time for formation of root primordia before exposure to the stresses of outplanting (Cram & Lindquist 1982; Dirr 1998; Hartmann et al. 1990), and cold moist storage should be considered as a pretreatment when testing an infrequently used species. Study of cutting storage has been limited to willow (Salix spp.) and poplar (Populus spp.). Cool moist storage may encourage root formation and root formation prior to planting may be undesirable. Some have suggested cold dry storage followed by soaking to reduce root formation (Jacobson, 2005)

Moderate levels of hormone treatment (0.3% IBA) have improved rooting ability in Scouler’s willow (Salix scouleriana) (Edson et al. 1995) other trials have indicated no benefit or even loss or rooting ability among indigenous species (Darris 2002a; Hoag & Short 1992).

Soaking stakes before planting may increase rooting ability, but results have been inconclusive (Hoag 1993). Increased soaking time may improve rooting ability, and soaking may allow cuttings to overcome the stress of dry soil conditions(Hansen & Phipps 1983; Schaff et al. 2002). However, soaked cuttings should be planted before roots rupture and emerge from the bark, which can occur in as little as two to ten days depending on the predisposition of the cutting. No systematic study of soaking has been made with indigenous species.

Wounded bark and cambium may cause rooting hormones, carbohydrates and rooting cofactors to accumulate near the injury, leading to formation of root primordia. This phenomenon is what leads to roots frequently emerging from the base of cuttings. Some difficult-to-root species may have improved rooting ability if numerous small horizontal slits are made in the bark on the basal half of the cutting. No controlled comparisons have been made with indigenous species.

Site Selection and Planting Methods

Cuttings must have adequate moisture, an oxygen rich rooting zone, and protection from desiccation to develop new roots.

High soil moisture in a planting site increases rooting ability as long as oxygen is present (Rein et al. 1991; Schaff et al. 2002). Although willow can form roots in low oxygen environments (Stannard & Guenther 1999; Zimmerman 1930), rooting ability is less than under oxygenated conditions (Pezeshki et al. 1998). For most species, adventitious rooting is strongly suppressed under hypoxic conditions, causing mortality of stakes planted under poorly drained conditions (Darris 2002a). This effect can be dramatic, with sudden increases in mortality caused by a few inches of elevation relative to ground water (Cereghino 2004). The relative survival and growth among live-stakes, bare-root, and potted material has not been compared among many species across moisture gradients.

Planting depth is determined by the need to have root primordia located in a region suitable for rooting. If the cutting is too shallow, there is the risk that the soil will be to dry for root formation. If the cutting is too deep, than labor and material resources have been wasted if root primordia are located in hypoxic soils. Planting depth recommendations are strongly affected by local climate and soils, with cuttings being planted as deep as 6 feet below the surface in arid sandy soils. Deep planting also affords stability to resist physical disturbance. Where soils

Paul Cereghino – 22 Jan 2006 Page 3 of 7 are moist or high water tables limit rooting depth, deep planting is unnecessary and a one-foot planting depth has been very successful, with most adventitious roots forming in the top eight inches of soil (Cereghino 2004).

Rubber mallets or dead-blow hammers (plastic and sand- filled) are preferred for installation to reduce the potential for splitting or breaking cuttings during installation. In hard soils, creating a pilot hole with a thin metal rod may reduce damage to cuttings. An oversized hole may reduce soil-cutting contact, preventing good water absorption and reducing root penetration.

Angled planting or burial under mulch or in a shallow ditch may increase the number of roots that develop where the rooting zone is shallow. Populus cuttings are often completely buried in agro-forestry practices (Morgenson 1992). Posts or large stakes can be installed at an angle overhanging creeks and ponds to provide immediate shade.

Some sources recommend painting the exposed ends of cuttings with latex paint, or a 50-50 solution of latex paint and water. Satisfactory results have been achieved without this treatment, but painting also allows for marking treatments in experiments, easy location of failed cuttings, clear identification of ‘which end goes up’ in volunteer plantings, and identification of species. Where desiccation stress is high either due to climate or species characteristics, sealing the end of cuttings may be more important for stake survival, and painting ends is commonly specified in arid lands. No controlled comparisons have been made with indigenous species.

Revegetation Strategies and Maintenance

If cutting stock grows more slowly, than more thorough site preparation or aggressive weed control may be necessary to support establishment of cuttings. Individual species may grow at different rates from stake plantings depending on environmental conditions. Planting density and site preparation is dependant on the degree of competition expected from weedy vegetation, the expected performance of each species, and coverage objectives. For some species, initial shoot and root growth after planting may be significantly less for cuttings than for potted stock, although this assumption has not been adequately tested for a range of species.

Cuttings can be planted at a high density to create immediate canopy for weed control. However, excessively close planting may prevent mowing maintenance. Some specifications call for planting stakes in groupings at wide spacing (10-12’) to ensure uniform coverage, while others recommend uniform planting at 2-6 feet spacing to achieve more rapid coverage.

Stakes can be planted through weed control fabric or mulch, or used to secure erosion control materials. A wide variety of erosion control functions (called biotechnical erosion control, bioengineering, or ground bioengineering), can be achieved using cuttings or a combination of cuttings, earthworks and other materials (Bentrup & Hoag 1998; Gray & Sotir 1996; Tuttle & Wenberg 1996). However the basic factors controlling stem cutting survival and growth remain the same.

Sample Specifications

MATERIALS wood. At installation bark shall Stakes shall be between 18 and 24 be intact and buds shall be turgid inches in length, with a minimum of and not showing signs of four nodes per stake. Side desiccation. branches and leaves shall be removed during or immediately Between harvest and installation following harvest. stakes shall be stored either: 1. buried under no less than 8 Stakes shall be of one- to three- inches of continuously moist year-old wood from parent stock and cold sawdust, bark, or free of disease or insect wood chips, or infestation. No dead patches shall 2. wetted and sealed in plastic be visible on bark and no sign of under refrigeration between fungal staining present on exposed 34-40 degrees Fahrenheit.

Paul Cereghino – 22 Jan 2006 Page 4 of 7 is”, with a replacement stake Stakes shall be harvested from placed in the vicinity, consistent parent stock growing within 50 with the planting plan miles of the installation site, at specifications. an elevation not more than 500 feet different than the installation Where soil has been prepared, site. Stakes shall be harvested stakes shall be installed without from source material growing in creation of a pilot hole. If full sunlight under similar stakes cannot be installed on moisture conditions to those found prepared ground, than additional on the planting site. preparation to reduce compaction will be required (see site prep Stakes shall be harvested from specifications). parent stock in accordance with applicable laws and ordinances, and Where a pilot hole is required on shall be harvested in accordance un-prepared ground for intact with property owner permissions and installation, the rod used to make specifications. Stakes harvested the pilot hole shall be thinner in from public lands shall not reduce diameter than the stake. The pilot individual plant stems by more than bar shall be reinserted and used to 25% and shall not remove stems from lever soil toward the stake more than 25% of individuals or following installation to ensure ramets (clonal shoots) in a stand good stake-soil contact (see figure unless eminent destruction of the ##). stand justifies indiscriminant harvest. Stakes shall be planted so that the buds point upward in accordance SPECIFICATIONS BY SPECIES with natural growth patterns. After planting, two buds shall INSTALLATION remain exposed to air. A minimum For ## days immediately prior to of 12 inches of stake shall be planting stakes shall be soaked below the soil surface (see figure completely submerged in cold, ##). oxygen-rich water. Stakes will be examined daily and planted Stakes shall be planted either immediately upon any evidence of singly or in groups at a spacing root emergence from bark. based on planting plan specifications for each species Stakes shall be harvested and (see figure ##). planted after leaf drop, and before buds have broken for spring growth. QUALITY CONTROL Deviations from these Stakes shall be planted in moist specifications may be permitted soils near field capacity. If with specific approval of the site soils show signs of hypoxia manager. (sulfurous smell or grey color) stake plantings will be halted in The site manager shall be given the those areas and the site manager opportunity to inspect quality- contacted. On level but slightly controlled stakes before undulating ground, planting crews installation. Stakes not meeting should avoid low spots wherever materials specifications shall not possible while meeting planting be counted toward planting plan plan specifications. specifications.

Stakes shall be whole and un-split The site manager shall be given the after installation. Stakes damaged opportunity to inspect stake during installation may be left “as plantings at the end of work.

Paul Cereghino – 22 Jan 2006 Page 5 of 7 Stakes not meeting installation specifications, inspection may specifications shall not be counted include random sampling of large toward completion of contract plantings to determine the rough requirements, and will be replaced. proportion of the planting requiring replacement, or another Where more than 1 in 10 stakes do mutually agreed upon method. not meet installation

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