Back: Table of Contents | Preparing The Site
PLANTING THE SITE
Once the site has been prepared and native plants have been determined as not to reestablish on their own, it is time to begin planting the native plant material. Make sure, whether planting seeds or plants, to know the time of the year most appropriate to do so for the particular species and type of material being used. For example, if the seeds require cold winter weather before they are able to germinate, and artificial exposure to those types of conditions will not occur before planting, they should be planted in the fall. Or, in temperate areas, rooted plants are typically planted in the spring, after the harsher weather of winter has finished. This gives them a whole growing season to establish themselves before winter sets in again.
The following sections detail some of the things that should be considered when seeding or planting the site.
Seeding Restoration Sites
If seeding is a good option for the particular species of native plants desired at the site, there are a number of things that should be considered when seeding the site. See the previous on Active Reintroduction: Seeds or Plants for the advantages and disadvantages of seeds versus plants.
Since seeds require moisture to germinate, seeding at a restoration site usually should take place at the time of year when a lot of moisture is available. For many areas, this is fall or spring. Summer plantings are possible if irrigation is available for that season. This will vary from region to region; different regions appear to have better results with certain seasons. Because native plants are not agricultural crops, they should not be planted on the same calendar. For instance, warm season grasses can thrive in June and July plantings.
Seed germination requirements should also influence the timing of the seeding. Different species may need to be planted during different seasons in order to maximize germination. If the seeds require stratification before germination they should be seeded at a time when they will receive that stratification. For example, many seeds in temperate climates require a cold, moist stratification. These seeds could be planted in the fall so that they are stratified during the winter and then will germinate in the spring. However, this method exposes the seeds to possible predation and other stresses for a longer period of time, so some restoration practitioners recommend artificially stratifying the seed and then planting when it is ready to germinate.
Seeding should take place soon after any final grading, contouring or other major site work is completed to minimize soil erosion and invasion by weedy species. Consequently, this work should be done just before the time of year when the seeds should be planted. If it will be a while before the seeds will germinate, it may be wise to consider using a cover crop or mulching the site to prevent excessive erosion before the site begins to revegetate.
Staggering the seeding of species over a series of years is another option that might be considered. Some restoration project managers recommend a phased seeding plan to introduce a few species first that can quickly establish. Then, in the following years or seasons of the year, other species can be interseeded to increase native plant diversity. In some cases, a "nurse plant" introduced first actually facilitates establishment of other species that are planted later.
Appropriate site preparation is important for increasing the chance of establishment and survival. If the seeds will be broadcast sowed, previous to sowing the site should have some type of surface preparation to the topsoil to create roughness for maximum germination success. Common techniques include the use of agricultural equipment to plow, harrow, chisel, disk, rip or gouge the soil surface parallel to natural contours (Munshower 1994). These techniques increase water infiltration and retention into the soil, increase soil aeration, and reduce soil erosion. Site preparation should take into consideration the fact that using the least possible soil disturbance is key to reducing weed competition.
An overly soft seedbed risks the chance of seeds being planted too deep. One rule of thumb that can be used as a field test is that a site should be firm enough for a 200 pound adult to not sink into the soil any more than ¾" with the heel of their boot. This may vary depending on the type of plant community being restored.
If the seeds will be drill seeded it is recommended to use a cultipacker or similar device to pack the soil, ensuring good seed to soil contact which is important for germination success (Morgan 1997). This should be done just before the seeds are drill seeded. Whenever equipment is to be used at the site, the tires and undercarriage should be thoroughly cleaned with high pressure spray to remove dirt and potential weed seeds from other job sites. If the seeds are broadcast sown, the packing should take place after the seeds are sown. An alternative method used with prairie seed is to firmly prepare the soil before drill or broadcast seeding, and then follow up seeding with a light drag or harrow to enhance soil to seed contact.
Effective seed mixes should consider a number of different factors (Diboll 1997):
- each species' ecological behavior
- efficiency of seeding technique
- germination rates and reliability of each species
- grass-to-forb ratio for herbaceous seed mixes
- restoration goals
- season of planting
- seed quality
- seeding rates and seed size
- site environmental conditions
Also, genetic considerations should factor into the selection of seed mixes. See the section on "Understanding the Importance of Genetics."
The seeds in the mix should be appropriate to the environmental conditions of the place where they will be sowed. If there are varying conditions in different parts of the site then it may be better to develop multiple seed mixes by matching species that are adapted to the specific environmental conditions. For example, if there is part of the site that is lower and moister and part of the site is higher and drier, separate seed mixes should be developed for the two different locations.
Of course, the mix should also reflect the goals of the project. The choice of plant species was discussed at length in the section on "Choosing the Appropriate Plant Species."
Since quite a few seed mixes are for restoration of native herbaceous species, another consideration should be the ratio of grasses and grasslike species to forbs (herbaceous plants that are not grasslike). For maximum diversity a mix with forbs making up 50 to 60 percent of the total weight is recommended (Diboll 1997). This may vary however depending on the particular plant community being restored and the cost of different forbs. For example, many native prairie sites species have a ratio of forbs over grasses even greater than 60 percent. For larger projects these ratios may be too expensive.
Seed quality is usually expressed as PLS (Pure Live Seed). This is a combination of how pure the seed is (amount of seed vs. amount of chaff, other non-viable plant material, and weed seeds), and what the germination rate is of the seed. For example, seed with a 90 percent purity and a 50 percent germination rate would have PLS calculated as shown:
|PLS||= 45 % PLS|
To get the desired amount of seeds to germinate, seeds with a lower PLS will need to be applied at higher rates than seeds with higher PLS values.
Seeding rates are sometimes expressed as the number of seeds or weight of seed per unit area (acre, hectare, etc.). There is little conclusive information available to determine correct seeding rates for particular native species because restoration sites and goals can vary greatly. Much of the information available is anecdotal. Seeding rates may be estimated from recommended seeding rates for similar commercially available species, from the number of plants expected per unit area, and/or by speaking with restoration professionals. Seeding rates should be increased for harsh sites (poor soils, steep slopes, low moisture, etc.) where germination and plant survival will be lower due to the harsh conditions. Seeding rates should also increase if competition from weedy species is expected. It may be desirable to seed natives heavily so they may establish to eventually outcompete weeds. In native plant communities, grasses generally establish more competitively than forbs, forbs more than shrubs, and shrubs more than trees (Munshower 1994). Some seed loss to birds, squirrels, rodents, and other fauna should be expected. Some seeds will simply not germinate because they were buried too deeply, dried out on the soil surface or were not viable from the beginning. Some seeds may be blown away by wind or washed away by water.
The seeding rate can be calculated using the PLS, the number of seeds per pound for that species, and the number of germinating seeds desired per square foot. Use the formula below to calculate the rate:
|= pounds/acre of seed required|
To calculate the amount of lbs/acre for each species by the proportion desired the number of germinating seeds per square feet can be multiplied by each desired percentage.
For example using the information given below and the formula just described the total number of pounds per acre of two species, A and B, can be calculated:
Total number of germinating seeds per square foot desired: 50
|% desired proportion||60||40|
|seed per sq. ft.||30 (60 percent of 50 seeds)||20 (40 percent of 50 seeds)|
|# of seeds per pound||60,000||80,000|
30 seeds/square foot * 43560 feet/square acre = 48.4 pounds/acre of seed required 60,000 seeds/pound * (45/100)
20 seeds/square foot * 43560 feet/square acre = 21.4 pounds/acre of seed required 80,000 seeds/pound * (51/100)
Remember that this final number of pounds per acre has already taken into account the purity and germination rate of the seed. With all the factors required to calculate the seeding rate, there is no truly accurate method of determining seeding rates at this time.
Some species are easier to seed than others. Certain species are more likely to seed successfully if some of the other plants have already germinated and established. These are seeds that should not be included in the initial seed mix, but could be seeded after two or three years.
Consider also how the species will interact with one another. Some species may be more aggressive than others. If these aggressive species are not adjusted to a smaller proportion of the total seed mix, they could end up outcompeting the less aggressive species in the mix.
The seeding rate should also be adjusted based on the type of seeding method to be used. Hand seeding is usually less efficient than mechanical seeding. Consequently, it is probably a good idea to increase the seeding rate if hand seeding will be the method used (Diboll 1997).
Seasonal differences in the seed germination rates should also be considered. Not all species germinate at the same time. If the project has seeds that have different optimal seasons for germination, perhaps the seeds should be divided up into different mixes, such as a spring mix and a fall mix. Availability of seed species will limit the mix as well.
Finally, budget will always play a role in determining species mixes. Some species are much more expensive than others, depending on their availability and the difficulty involved in collection and cleaning. It is never an easy decision to determine whether some species are not cost effective. This is where an understanding of the plant community being created becomes important. What role do those species play in the community? Are they a matrix species? Are they an important wildlife habitat plant? Are other plants in the community dependent on this species to help maintain the community balance? Please take into account that sometimes costly specifications are not expensive due to the diversity of a long species list, but because of an overly heavy seeding rate based upon agricultural methods for pastoral grasses using around 50 lbs/acre.
The most important goal for seeding a site is to place the seed at the proper soil depth that will ensure its germination and successful growth (Munshower 1994). Different seeds have different light, moisture, and temperature requirements. Therefore, the optimal placement depth in the soil is different for different seeds as well. Generally, smaller seeds germinate more readily close to the surface, while larger seeds can be buried more deeply. Because native seeds vary so widely in their germination requirements, it is difficult to choose the best conditions for all species in one single seeding technique (Munshower 1994). Therefore, it is ideal to estimate average conditions for seed mixes with a variety of species or to do a few different seeding treatments if possible. There are a few types of seeding techniques commonly used for restoration:
Drill seeding is normally used for species with large seeds and may be accomplished with specialized agricultural equipment or with hand-held seed drills. In either case, the seed is placed below the soil surface so it has protection and potential for good soil water contact. The advantages of using drill seeders is that due to their ability to place the seeds at a precise depth, they have a higher germination rate and so can be more efficient. The disadvantages can be the cost of purchasing a drill seeder or the difficulty of renting one for the correct time, their need for very clean seed to operate effectively, and the fact that the seeds planted are in straight rows, creating a less natural look (Morgan 1997).
Broadcast seeding places seed on the soil surface instead of underground. This can also be accomplished with agricultural equipment like fertilizer spreaders or by individuals operating hand spreaders. Adding an inert carrier such as horticultural vermiculite, perlite or sand to the seed mix can help make the seed mix easier to spread and help to track where the seed has already fallen (Morgan 1997), although some disagree with these additions and do not use them in projects. Normally the ground is raked or harrowed before seeding to break up the surface and after to allow seeds to fall into crevices which help retain moisture for germination. The ground can then be packed with a cultipacker to press the soil in against the seeds. It is not recommended to use this method on a windy day as a lot of the seed might blow away. Broadcast seed application rates normally need to be higher than drilled seed rates because they have a lower germination rate. However, the advantage of broadcast seeding is that it is cheaper, easier, and creates a more natural look.
This is a type of broadcast seeding in which seed is applied to the soil surface in a liquid (usually water) from specialized high pressure equipment. This method is often used for steep or rocky slopes, and otherwise difficult terrain. Mulch may also be applied in this manner as hydromulch, but it is recommended to apply this after seed is applied so the seed does not end up on top of the mulch where it could dry out and fail to germinate (Munshower 1994). It is also key that this mulch does not form a mat that shades out emerging seedlings. "Tackifiers" are often used to help the seed or mulch "stick" to the soil surface.
This is another type of broadcast seeding in which seed is dropped from a fixed-wing aircraft onto the soil surface. This is most effective for extremely large or otherwise inaccessible areas (Munshower 1994).
Local Native Hay Seeding
This is a type of seeding where local native grass (weed-free) is cut and baled with the seedheads still intact. Up to 2 pound of local native seed per bale would be seeded on the site when the local native hay is spread out as mulch.
Adding weed-free mulch to the site after it has been seeded offers many benefits for successful seed germination:
- provides physical substrate for the seeds so they are not blown or washed off site
- provides physical protection for the seeds from extremes in temperature, light, and moisture
- provides additional source of local native seed if local native hay is used
- retains moisture which is important for successful germination
- reduces soil erosion
Mulch can take many forms (organic and inorganic), and all have advantages and disadvantages that vary widely between restoration sites. Some examples of mulch materials are: bark, wood chips, weed-free straw, leaves, weed-free local native hay, crushed stone, black plastic, newspaper, and erosion control fiber mat materials. The mulch should be applied in such a way as to not suppress seed growth when the seeds start to germinate. In other words, it should be applied in a thin enough layer so that the seeds (especially small ones) would not be buried too deeply.
Sometimes it may be useful to use a cover crop to help protect the site from soil erosion as well as provide safe sites for seedling germination until the native plants that were seeded are able to establish. Cover crops are usually some type of sterile annual weed-free grain that will grow rapidly, establish for the first year, and then fade out as the natives become established. Oats, barley or REGREEN are recommended over wheat or some types of rye because the wheat and rye have been found to have a more competitive effect on the seeded natives. However, early successionals such as Canada Wild Rye, a cool season native grass, are also useable. If possible, to help ensure that the grain does not persist at the site, it is recommended that it be mowed before it produces seed.
Planting Young Plants
Careful and correct planting techniques are critical to the survivability of young transplants. Environmental conditions will vary widely among sites, but the following general guidelines should help ensure success.
- Choose a day with moderate weather conditions. Try not to plant on days with extreme heat, cold, moisture or wind.
- Minimize root exposure before planting. Do everything possible to prepare for planting before removing the plant from its container or other root protection. Collect all necessary tools, distribute plants around the site to their expected locations, prepare the water supply, dig the holes, and any other arrangements necessary.
- Make each planting hole twice the diameter and just slightly deeper than the height of the container or rootball. Planting holes for bare-root plants need to be large enough so the roots are not crowded together in the hole. The cross-section of the planting hole should be bowl or lens shaped instead of cylindrical because the roots need to spread horizontally to the surface to take advantage of available oxygen. The larger and wider the planting hole, the better.
- Roughen the sides and bottom of the planting hole with the sharp edge of a shovel or other implement. One of the greatest difficulties for transplant roots to overcome is to breach the planting hole/new soil interface. Roughening the surfaces of the planting hole provides easier access for the developing root to enter the new soil. When working in an arid climate, watering the planting hole thoroughly prior to planting will assure the availability of soil moisture to plant roots as they grow down into the native soil.
- Place some of the backfill soil into the bottom of the hole in a mound and firm it down.
- Remove the plant from its container, wrapping, burlap, wire basket or other covering. Once the plant is removed from the container, it should be planted immediately to prevent death of roots.
- Prune off any broken, twisted, dead, circling or diseased roots. Loosen and brush off soil around the periphery of the root ball.
- For container-grown plants, "butterfly" the bottom half of the root ball by spreading the roots apart. Lay the root ball on its side and slice with a sharp implement two-thirds of the way up the root ball starting from the bottom. Fan the two cut halves out to the sides. This is recommended to help plant establishment and reduce the chance of root girdling.
- Place the plant in the hole so that the roots are spread out over the mounded soil and the base of the stem is slightly above the soil line. If necessary, hold the plant suspended in the hole to keep it upright while backfilling with the other hand.
- Generally, adding amendments such as organic material or fertilizer just to the soil used to refill the hole is not thought to aid in plant establishment. (Pellet 1971; Whitcomb 1979a; Corley 1984; Davies 1987; Hodge 1990 in Harris 1992) Ideally, the native plants will acclimate to the soil conditions of the site and survive without additional nutrients in the planting hole. Nitrogen is the most common nutrient lacking in soils, so a nitrogen fertilizer could be added at the surface and watered in. It is not recommended to place fertilizer in the planting hole because it could burn the roots.
- Backfill soil around the roots firming it using hands or feet after every few inches. Take care not to damage the roots and be sure the roots are still spread out.
- Do not bury the stem of the plant, make sure it is still at or above the soil surface. The soil surface in relation to the stem of the plant should be at the same level as it was in the container. Continue until the hole is filled with firm soil, gently pulling up and settling down the plant to eliminate air pockets.
- Create a berm around the perimeter of the planting hole that will hold water.
- Water the plant, wetting the entire planting hole basin. Be sure to let water flow downward and soak into the soil, then water again. The first watering flushes air from the soil pores; it is the second watering that will provide water available for the plant's use.
- If possible, mulch around the base of each plant. This will reduce weed competition, mediate soil temperature extremes, and reduce moisture loss from the soil. Mulch should not be allowed to touch the trunk or crown of plants and should be placed at least 1" away.
Depending upon the environmental conditions at the restoration site, measures may need to be taken to help new transplants survive. Staking plants, especially in windy areas, may be necessary. Protective tubing, netting or screening may be utilized to protect young plants from herbivory, harsh sun, wind, cold, or machine or foot traffic. There are a wide variety of products for these purposes available from nursery supply catalogs. It is important to remove any protective devices when they are no longer needed so they do not impede the growth of plants.
To encourage the roots to spread out from the container soil into the native soil, it is important that sufficient water is applied to wet the area of native soil outside and below the rootball and container's potting soil. The amount of water the new transplants need will again depend on the site conditions and the weather patterns. Some native plants will initially require watering until they have become established at the site. Whatever watering regime is decided, the frequency of watering should decrease over time to allow the plants to acclimate to the site and eventually survive without any additional watering.
Using Volunteer Labor
Using volunteers for a restoration project can be extremely valuable. In addition to providing much needed labor, the public can be educated about the value of ecological resources, the need for restoration, and the importance of good land stewardship practices. It also may provide them with a stronger feeling of connection to their local environment. By instilling in them that sense of "ownership" of a restoration site, they become more inclined to continue to visit the site and provide information about disturbances and detrimental changes occurring there. However, it is also important to remember that volunteers do require adequate training and supervision to ensure that the work is done correctly. Using volunteers as a cheap source of labor without adequately supporting them could be detrimental for the project.
When using volunteers in a restoration, here are some basic guidelines to follow:
- Be organized and know, before they arrive, what work the volunteers will be doing.
- Inform volunteers that their efforts (sweat equity) develop project ownership so they treat and enjoy the site as their own.
- Use color-coded flags to mark the planting locations of individual plants. Use a different color for each species or write the initials of the species on each flag. Marking individual locations eliminates the chance that volunteers will plant a particular species in an inappropriate location.
- Provide adequate, clear training and supervision. Keep in mind that the volunteers will have varied backgrounds, with some needing more information and training than others. Make sure that all volunteers are provided with enough information and training to ensure successful implementation or management of the restoration project. Written or graphical training materials are usually appreciated and well-received.
- If the same volunteers will be working at a site over a long period of time, be sure to provide enough training and encouragement so that they want to return. Remember, they are providing a much-needed service at no cost.
- Show appreciation. If the budget allows, providing food and/or t-shirts is always a popular. Otherwise, a simple "thank you" goes a long way.
To find volunteers, contact the extension agency, local native plant or gardening clubs, other community organizations or advertise in the local media. Also, look to nearby neighborhood primary and secondary schools, as well as universities, for student volunteers of all ages.
Next: Caring For The Site