A Guide to the Revegetation and Environmental Restoration of Closed Landfills

Chapter 9 and 10

Chapter 9: Planting of Vegetation

Installing the various components of the final vegetative cover will require an assortment of planting techniques, depending upon the complexity of the planned vegetation community and the project site conditions (slope steepness, etc.). The landfill design (cover thickness, etc.) could influence how the plants are prepared for planting on a case-by-case basis.

Seeding

Application by this method may vary with plant types.

Grasses and other plants started from seed may be sufficiently planted by spreading seed with some type of disperser—by hand, by vehicle, or aerially. No tackifiers are used to hold seeds to the soil. Requires watering and fertilizing after planting.

Hydroseeding is the use of wet seed, fertilizer, and adhesive mix, and sometimes mulch, in a slurry that is sprayed by pressure gun onto the ground. A single application will provide adequate coverage. This process is primarily for grasses or wildflower dispersal in carpets of cover. Green dye can be added to the mix to make it "look" like grass and aids in determining the areas covered and not covered.

Hydroseeding is excellent for covering of new ground in the first year's soil stabilization and protection stage. It is effective on steeper surfaces or areas where soil compaction or marring by vehicles must be avoided. It is used best for annual grasses but can be used with perennial grasses. Several hydroseeding procedures are available, including:

• One-step. Seed, fertilizer, binders or other additives sprayed onto site at once.
  
• Two-step. Seed and stabilizing fiber spread first with mulch spread over the seed.
  
• Two-step, with blanket. The seed and fiber are spread first, followed by a fiber blanket.
  
• Drill-seed. The seed is spread and "disced" into the soil.
  
• Two-step prep and drill. Soil amendments are applied first then the seed is spread and disced.

The seed mix is dry and placed in a rotary disperser, usually on a vehicle or small trailer mount. This is moved across relatively level surfaces to disperse dry seed. Fertilizing and moisture must be provided in separate steps. Dry seeding is economical and good for small tracts of land.

For large tracts of land, the seed mix is spread from a small aircraft. This process is best for grassland seeding in an open area as aircraft maneuvering would be a consideration.

Planting done either with hand tools or mechanical planting machines. Some plants require seed placement under the soil surface for proper germination and seedling survival. This will require more labor-intensive techniques to plant seeds individually with crews on foot or possibly machines on more level ground.

Table of Contents

Small sprouts or seedlings 1 to 2 feet high will require use of field crews to walk over the site and plant them by hand. This will insure proper depth and usually a dose of fertilizer in the hole will help the seedling survive.

Perennial grasses can be planted this way in small "plugs." This is considered the best means for perennials as it provides a "head start" against annual grasses in dry conditions.⁹

The planting of trees and shrubs may require some machine assistance, possible use of augers to place the hole, carrying containers and placing the plant in the hole. Several workers, as well as a small hoist may be needed in handling large containerized plants. Advanced skills in nursery care and planting will be required to insure proper preparation and planting of the vegetation.

Table of Contents 

If a ready source of larger trees or shrubs is available, transplantation companies and equipment are available to facilitate the need.

An assortment of mobile truck-mounted transplanters is available, enabling the quick removal, digging of the hole, and planting of the tree. The transplanting is accomplished with a specially designed blade that encircles the tree root ball. Several blades drop vertically into the soil around the tree or large shrub, collecting the root ball within. Hydraulics closes the blades together and lifts the entire tree out of the soil for placement at the new site.

Trees up to approximately 20 feet tall are transferable with this system. Several trees can be moved on a flatbed truck to the new site. This procedure is good if the operator maintained a tree nursery on site during the operation of the landfill, or has access to a vegetation source elsewhere.

Consideration should be made regarding the type of tree being transplanted and its size. Smaller trees are better candidates for transplanting as they are easier to move and will require less pruning of the crown in preparation for transplanting. This will reduce potential shock to the tree. If a site is being prepared for a landfill or future cell of an existing landfill, saplings on the site can be transplanted to a holding nursery area and be maintained until the site is ready for closure. The larger saplings can then be transplanted back to the original site.

Container Removal, Root Preparation. Before large plants are placed in the ground, their containers must be removed and the roots loosened in the root ball to encourage root growth once in the soil.

• Containers
  Removal of plastic, metal, or wood containers prior to root preparation and planting is encouraged. Hard containers, if not removed from the roots, will restrict root development and most likely kill the plant. Burlap-wrapped plants may be planted with the burlap wrapping in place; it would still be best to remove the burlap, which will permit faster root development.
  
• Grooming the Root Ball
  This action is for better root development and nutrient absorption. Loosening the outside roots will allow them to spread out and into the surrounding soil more rapidly. This will facilitate moisture and nutrient absorption and plant support. Care must be exercised not to disturb the root ball too much, which can disturb the interaction between the plant and its root bacteria. Retaining as much of the native soil in the root ball is important to preserve the plant and bacterial relationship.
  
• Trimming of the Tap Root
  This action will allow planting of small young trees in shallower soil layers without the roots disturbing lower cover layers. A young tree can grow without the taproot as its laterals can reach about three times the mature canopy width. An un-trimmed taproot can penetrate through the barrier layer of a landfill final cover and promote unwanted moisture invasion into the waste.
  
  An alternative is to purchase bare root trees and shrubs. These are prepared for planting with no container or burlap wrapping around the root ball. They are usually less expensive than the containerized forms just discussed and can be more resilient to the transplanting process, which will improve their survival.

The project operator will need to provide a supply of plant stock to replace that removed for the project. There are several means of having replanting stocks available. Some techniques can require some forethought and planning to carry out.

When the project is about to begin (constructing the landfill for use), the operator can plan to set aside some adjacent land at the site or on a nearby parcel, preferably in an area with the same soil type as the project site. This will provide a nursery area for plants transplanted from the project site.

Smaller trees and larger shrubs on site can be removed with transplanting equipment and moved to this nursery site. When the project has reached its life span and closure is finished, the transplanted plants stockpiled at the nursery site can be transplanted back to the landfill. This may take some initial expense at the outset, but the replanting of these larger native plants may be cheaper in the long run than buying comparable nursery stock, having it transported to the site, and planted.

When the excavation for a new landfill project starts, the operator can have the topsoil stripped and placed in a holding area for later use in the closure phase. This topsoil will contain seeds deposited by the vegetation that is on-site. When the project is completed, this topsoil can be dispersed over the final cover vegetative layer. The seeds contained in the soil will germinate upon irrigation and continue the vegetative community that occupied the site previously.

Prior to removal of the vegetation and excavation, seed collection directly from the vegetation on-site can be carried out. The mature seed can be collected and, if, properly stored, will survive for several years. This material can be cultivated in a nursery site as an alternative or it can be directly re-deposited on the closed and prepared site upon final closure. This procedure can be labor intensive because harvesters must pick seed from the plants. Sometimes they use special seed harvesters called "grin reapers."

There are two choices for plant stocks.

• Native Plant Nurseries. There are specialized nurseries throughout California that raise native plant species. Access to these suppliers will provide the majority of the more common native plants found in California. A nursery should be available within a relatively close distance to the project location to provide native plants indigenous to that area. A listing of some native plant nurseries is included at the back of this Guide.
  
• Landscape Nurseries. For projects that plan on landscaped projects such as golf courses or parks, most standard cultivated plant nurseries should have plant stocks to satisfy the revegetation needs of the project.

Table of Contents 

Chapter 10: Six Concepts for a Successful Restoration

The following six concepts can assist the operator in creating a successful revegetation or restoration program:

1. Surface Conditions. Establishing stable surfaces and drainage conditions that are compatible with the surrounding landscape will make the project blend in with the local terrain. This will be accomplished through proper planning, by materials placement and grading during operations, as well as after closure by final fine grading and naturalized contouring.

2. Proper Soil Surface. Preparation prior to vegetation placement may ensure higher seed and plant establishment. Texturing helps keep seed on the soil surface, especially on slopes. It aids in retaining water, allowing it to percolate into the soil. Texturing also helps slow down-slope water flow, reducing slope erosion. Surface texture preparation can be accomplished with assorted texturing aids.

Figure 10 Soil Surface Texturing Rollers (11 KB)

1. Land Imprinter. A specially designed roller for dry or arid conditions, the imprinter employs a unique set of textured rollers to place depressions into the soil. The roller is designed to penetrate the topsoil surface without overturning it as in plowing or discing procedures. This breaks open the hard crust that usually accompanies desertified land, allowing freer air and water exchange.
   
2. Vegetation material on the soil surfaces remains on top to serve as a protective layer for seedlings, rather than being turned under the soil. The texturing promotes water retention with short depressions but it limits surface flow of water that can occur with disc furrows.

   The water is directed along transfer grooves and then is trapped in "funnels" to soak into the soil. Plant seeds and nutrient material can be collected and remain in these depressions.
    

3. Sheep’s Foot. A sheep’s foot consists of a set of heavy steel rollers with thick block-like projections (cleats) that impress shallow holes into the soil surface. It is either pulled behind a tracked or rubber tired tractor or integrated with its own engine and a set of steering wheels with single or front and rear rollers. Another version, similar to a sheep’s foot but having rollers fitted with short blunt-tipped spikes on the drum, creates a grid-like pattern of holes in the soil.
   
4. Grid Roller. A grid roller employs a cylinder constructed of heavy bar stock set annularly and longitudinally, in a basket weave on the outside "surface", creating a cage-like drum. This surface impresses grid-like grooves into the soil, with resultant positive knobs of soil between them.
   
5. Tractor Walking. By using a tracked tractor, the soil can be textured with the "grousers" (traction lugs) to create shallow grooves in the soil surface. The tractor must be operated along the slope to create short grooves across the slope axis. These grooves can retain seed and other soil surface treatments such as fertilizer pellets, straw, compost and mulch. This process is not as effective as the other systems because the depressions are shallower and less likely to retain seeds and nutrients against wind or impede down-slope water flow as effectively.

3. Vegetation Survival. Where possible, create surface and substrate conditions closely approximating the native soil that will be conducive to seed germination, natural regeneration, and native plant establishment. Texturing the soil surface with tractor walking, grid-rolling, or other means of roughening the soil to retain seeds will help seed and moisture retention and growth.

Vegetation should have a wide range of growing rates. The faster-growing plants will provide initial soil binding and protection for the slower-growing, but larger, plants to establish themselves. When possible, provide water sources without artificial irrigation by using moisture enhancement catchment basins on site, adjacent to the actual landfill. These can be naturalized to assume a more pond-like appearance. The soil surface will be altered through grading, surface texturing, and the selective application of seed or appropriate soil material that will act as a seed source. These conditions, of course, should not compromise the functions of the final cover. Research in providing subsurface landfill gas barriers beneath built-up berms for larger trees and shrubs has shown a positive effect in protecting the plants from gas migration (CO₂, CH₄) into the root zone. These barriers entailed a gravel substrate underneath a plastic sheet liner, and vent piping to the surface, covered with the topsoil berm. A clay liner under the berm served the same purpose, providing a porous pathway for gas to migrate around the root zone to the atmosphere.

4. Seed Stocks. When possible, collect and use seed from the native plant species obtained from local and on-site sources, and transplant locally adapted plant species into specially prepared nursery spots on site. These plant source sites will act as loci for continued natural revegetation on the entire reclaimed site, including decks, side-slopes and benches.

5. Terrain. When practicable, create features that may mimic local surface features to resemble the surrounding terrain. These surfaces must be contoured to be in compliance with regulatory requirements of Title 27, etc., but may still reflect natural profiles. Research in this field is yielding successful results.

6. Safety. Consider public safety (especially parks or public accessed lands) through the stabilization of slopes and excavated surfaces. Removal and/or fencing off structures or areas that could constitute a public hazard may be necessary.

Table of Contents  |  LEA Central

Last updated: April 18, 2008