Seeds and Planting Oak Savannas

Recovery of the understory vegetation is a principal activity of oak savanna restoration. Planting requires extensive preplanning and careful consideration of the goals of the whole restoration project.

Planting on bare ground

If there is no potential understory vegetation, for instance, in a heavily grazed savanna, it is best to kill off all existing understory vegetation with a broad-spectrum herbicide such as glyphosate, and then plant the whole area from scratch. This approach is similar to what is done when prairies are planted on former agricultural fields.

Planting a degraded savanna remnant (Interseeding)

If the savanna has not been recently grazed, or perhaps has never been grazed, then restoration involves interseeding. The decision to interseed rather than kill everything except the trees and start over will be based on the details of the specific site. Packard has published a nice summary of the principles of interseeding of both prairies and savannas.

Interseeding will probably be the technique most used in oak savanna restoration. According to Packard: “Interseeding is a good way to restore remnants—for even in poor-quality remnants, the turf of existing vegetation is often a better starting place for seeds than tilled earth.”

Interseeding can be viewed as an enhancement approach to restoration, relying on the fact (or hope) that there may still be “good” plants already present.

Seed sources

Whether planting bare ground or interseeding, the most important requirement is the availability of a high diversity of appropriate savanna understory species. Depending on the circumstances, seeds can either be purchased or collected. Purchasing is very easy but expensive. Collecting is time consuming, but ultimately very satisfying. Collecting also requires the existence of suitable areas from which seed can be collected.

How many species and what sort of seeding rate? Data from practical restorationists indicate that the more species the better, and the higher the seeding rate the better. However, unless the budget is unlimited, compromises will be made in satisfying both of these prescriptions. Existing data on species numbers for oak savannas should be used as a basis. At least 100 species should be used in the initial planting.

Seed collecting

The ideal locations for seed collecting are remnant prairies or savanna remnants. The latter are often much more degraded than prairie remnans because of brush or tree invasion. The goal is to use seeds that are local to the area, often called "local genotypes".
 
Seed collecting locales
Source Advantages Disadvantages
Public prairies or savanna remnants Rare species; local genotypes Not common; permission may be difficult to get; quality of seed uncertain
Planted prairie or savanna Large variety of plants; ease of access Source of genotype may be unknown; permission needed
Railroad prairies Local genotypes Probably only a few species present; permission may be difficult to obtain; difficult access; safety issues; quality of seed uncertain
Roadside prairies Local genotypes Probably only a few species present; permission may be difficult to obtain; difficult access; safety issues; quality of seed uncertain
Private lands   Probably only a few species present; permission may be difficult to obtain; source of genotype uncertain; quality of seed uncertain
Seed production beds Good control; local genotypes; usually high quality seed Expensive and time-consuming to set up; weeding and watering needed
 

Seed collecting dates

Tables are given providing data with appropriate dates for collecting different species of savanna plants. One table is arranged in approximate chronological order. The other table is arranged in alphabetical order by Latin name.

The dates must be considered only a guide. At a given site, there will be considerable year-to-year variability in seed maturation dates, due to variation in weather. There is also site-to-site variability, depending on location as well as weather.

Considerable experience is needed when deciding if seeds of a given species are ripe. Populations of desired species should be located well ahead of time, while still in flower, and assessed frequently for ripeness. Using the tables as a guide, the species of interest should be checked frequently beginning well ahead of the date shown in the tables. Check the seeds early and, if possible, continue checking at half-weekly intervals (weekly intervals at the longest). Maturity should be checked carefully with a fingernail and in some cases with a hand lens.

Some species retain mature seeds for long periods of time, whereas others lose their seeds quickly.

There are no guidebooks to these variations.

The ideal situation for the novice is to work in the field with experienced seed collectors. Volunteering for seed collecting activities with groups that have a lot of experience is highly recommended.

 

Seed collecting procedures

The tools of the seed collector include gloves, a good hand clippers, a large supply of grocery bags of various sizes, and a collection of plastic buckets. Buckets can be purchased at building supply stores or hardware stores. Also, cast-off buckets from grocery stores or restaurants may be available gratis. To keep the hands free for collecting, a rope or sturdy strap should be used. An alternate is to fasten the bucket to a belt loop with a caribiner.

The seed collecting technique varies with the species. A few tips are given here.

• For species with large seed heads such as those in the sunflower family: gather the stalks of the seed head together and cut as close to top as possible, and then drop into the bucket. As the bucket fills up, press the seed heads to the bottom. When the bucket is jammed full, transfer the collected material to a large bag and return to the collecting site.

• For species making structures with loose seeds, such as shooting star or prairie cinquefoil: cut the flower stalk below the lowest seed container, carefully place the stalk into the bucket and then turn upside down so that the seeds drop in the bucket. Knock the stalk against the bucket to release more seeds, and then discard the stalk.

• For species whose seeds strip well (grasses, some asters and goldenrods: pull the seed head over the bucket while still attached to the plant, and then strip the seeds directly into the bucket.

• For species that make berries: pull the seed head over the bucket and strip off the berries.

• For milkweeds or other species that make seed pods: cut each pod just below the stalk and drop into the bucket. Later, remove the seeds and let the “fluff” fly away (a windy day helps).

• For carrot family species: gather the seed head together over the bucket and cut the stalks above where they join, so that each umbel breaks apart.


Seed collecting technique

Stiff goldenrod (Solidago rigida) flower head
Stiff goldenrod seed head
 

Seed collecting technique. The bucket is fastened to the belt, keeping its position low and allowing the hands to be free. The seed head is pulled over the top of the bucket and then cut.

At right: close up photograph of seeds, showing the characteristic "fluff" that most members of the Aster family possess.

 

Seed drying and cleaning

Seeds should be well dried, either in the sun or in a low-humidity environment. A basement or storage room with a well-ventilated gas heater is ideal. The seeds should be spread out on tarps, sleds, or specially built trays. If space is available, they can be spread out on a concrete floor.

The seeds should be turned occasionally, and allowed to stand until they are all dry. Even if the seeds seemed dry in the field, they will have enough moisture so that they will need drying. Feel the seeds with the bare hand to determine if they are dry. If the seeds are not dry, they will become moldy. Seeds are rarely released in pure form from plants. Most species have seed coats, or come off the plant attached to “fluff” that is involved in seed dispersal. Some species bear their seeds in fruits. Each species has its own peculiarities, although asters, goldenrods, and other members of the Asteraceae all produce seeds of similar character. Purification involves extensive manipulation by breaking up the crude seed heads, screening, sifting, and (perhaps) blowing chaff away in a fanning mill. In most cases when planting a savanna restoration, highly pure seeds are not needed.

Once the seeds are dry, they should be cleaned. The goal here is to remove all stems, seed coats, and other chaff. Unless they are to be used for a special research study, the seeds do not need to be highly purified, but large sticks and debris should be removed. How clean they should be will depend on the manner by which they will be planted. If a mechanical planter is to be used, then the seeds need to be cleaner than if they are to be hand broadcasted.

Home-made trays for drying seeds. The rack in the background is on wheels so that it can be pushed out of the rain. The hammermill is used to release seeds from their pods or seed heads.
 
Hand screening compass plant seeds.
   
(Right) The hammermill is very useful for processing seeds. It breaks up the seed heads and releases the seeds. Once released, the seeds can be further purified by screening. Although expensive, a hammermill is essential for any substantial restoration project. Nonprofit organizations can often combine resources and share such a piece of equipment. Individuals may find it possible to trade volunteer labor at a larger restoration project for use of the hammermill.

 

Tray of milkweed pods
Clean milkweed seeds

 

Once cleaned, the seeds should be stored in brown paper grocery bags. Plastic bags are not recommended because they will not allow moisture to escape. Be sure to label each species with name, as well as date and location collected.


Species vary widely in the size and shape of their seeds and the restorationist should become familiar with the structures of all species being used.




For storage until planting time, seeds should be stored in clean, heavy-duty bags. These bags can be purchased at any agricultural feed mill. If they are to be stored for the winter, they should be hung up so that rodents cannot reach them.

Commercial seed sources

Commercial seed companies specializing in prairie and savanna restoration may also be a source of local genotypes. Good companies will know the sources of the seed stock that was used to establish their seed production beds, and will specify that information on the label. Restorationists should obtain advice about good seed companies in their area from experienced local people.

Planting

Seeds can be planted either in the spring or fall. Fall planting is ideal, since the seeds then overwinter under conditions that mimic those in nature. However, it is essential that planted seeds reach bare ground, which usually means after a burn. Although fall burning is often excellent, it depends upon favorable weather conditions, and may be thwarted by an early winter.

If planting must be delayed until spring, hang seeds in an outdoors protected location such as a barn, screened in porch, or unheated basement. For large-scale storage, commercial feed bags, available at an agricultural co-op, are recommended. Wherever they are stored, they must be protected from rodents.

As soon as spring burns are finished, the seeds should be planted.

Pure live seed and seeding rates

Quality of seed plays a major role in the success of a planting operation. Seed viability can vary markedly from year to year, depending on the weather during the period of flowering and seed setting. Seeds purchased from commercial sources have the advantage here, because they are sold on a Pure Live Seed (PLS) basis.

Purchased seed has two major drawbacks: it is expensive; and it may not be local genotype.
The variable quality of seed is one reason that restoration sites should be planted more than once. Each year is different, and quality of seed varies, so some species may become established one year and not another.

Determining seed viability is not complicated but requires technical knowledge which the seed testing laboratory provides. In the Midwest, there are commercial seed testing laboratories as well as testing laboratories associated with agriculture universities.

Suppose the percent viability of the seeds is not known?

The Natural Resources Conservation Service (NRCS) specifies practices which may be applied as part of conservation management activities and are permitted for landowners supported in part by Federal grants. These practices are also applicable even if government funds are not involved.

For instance, if the seed used was hand collected from a local source, the NRCS specifies a minimum seeding rate of 50 seeds per square foot. An additional provision is that the seeding rate should be adjusted so that no single species amounts to more than 20% of the seeds in each square foot. NRCS also specifies that at least 25 seeds per square foot must be native grasses or sedges and at least 5 species of grasses and 15 species of forbs and legumes must be seeded. These criteria are applied by NRCS for both prairie and oak savanna restorations.

Note that the number of species given in the previous paragraph is a minimum and great effort should be expended to plant more species. If only small amounts of hard-to-get species are available, then they should not be placed in the general seed mix, but hand planted separately in suitable parts of the savanna.

Seeding by weight or volume instead of numbers

Many restoration plantings use weight of seeds instead of number. For instance: “Use about 10 to 15 pounds of mixed forbs and grasses per acre using at least twice the weight of forbs compared to that of grass seed. Use a 10-pound rate for certified seed and a 15-pound rate for hand-collected seed.”

Whether weight or numbers, the more seeds the better. Some people use seeding rates of 25 or even 50 pounds of seed per acre. Research has shown that the higher the seeding rate, the higher the species diversity in the final planting.

Packard also suggests seeding rates based on volume of seed. For instance, one cup (16 ounces) per 100 square feet or “one kitchen garbage bag to 18,000 square feet (a bit less than half an acre). Such a seed mix would consist of 50 percent seed (with the heads broken up but chaff retained) and 50 percent perlite.” Instead of perlite (an insulating product available at lumber yards) sawdust can be used as a seed carrier.

Seed mixes for savanna restoration

Because of its heterogeneity, the savanna being planted never provides a single type of habitat. It is convenient to think of the planting unit as a mixture of four types of areas: prairie (0-10% canopy), open savanna (from 10-30% canopy), closed savanna (from 30-70% canopy), and woodland (greater than 70% canopy). Each type of area should be marked and an appropriate seed mix used for each one.

To organize the planting, walk the area with the head to the sky and locate areas with very few trees (prairie), scattered trees (open savanna), woodland areas with occasional openings (closed savanna), and woods without any openings (woodland). If a recent (post-restoration) air photo is available, it can be used to locate these various areas.

An oak savanna species list that categorizes principal native species according to their canopy preferences is provided here as a PDF.

The Pruka and Curtis species lists provide brief overviews, and the Bader list provides much greater detail.

These lists are just representative of what can be used. A lot will depend upon the region of the Midwest, and the species for which seeds are available.

The quantity of seed planted will depend in the first instance on the amount of seed that has been collected, or purchased. Again, recall the dictum that the higher seeding rate and the more species the better.

Initial stages of making a seed mix. The various species are measured out and added to the mix.

Mixing the seeds. Sawdust has been added as a carrier. This especially helps to keep the very fine seeds from settling out. It is important that the seeds be well mixed.

 

The seed mix is distributed to buckets to carry to the field.

 

Seeds can either be hand-broadcasted (as is being done here), or planted with a mechanical tractor-pulled device such as a fertilizer spreader or drill planter. For hand broadcasting, a light snow is very helpful (but not essential).

 

Nice even distribution of seeds is shown in this pattern on the snow. Most of the material visible is sawdust, but by getting down on the snow it is possible to see single scattered seeds.

 

For a large planting acreage, mechanical equipment might be used. This rig uses a fertilizer spreader that has been adapted to use for seeds. A device in the bottom of the hopper keeps the seed mix stirred while it is being distributed.


Calculating seeds per square foot

The recommended planting rate by the NRCS is 50 seeds per square foot. With crude or partially cleaned seed, how does one estimate the amount to use?

Here is a procedure adapted from Kurtz. It is for the amount of seeds per unit weight of a single species, and assumes the species has been partially cleaned.

1. Select a representative sample of the partially cleaned product.
2. Remove a small amount and separate the seed from remaining straw, flower parts, fluff, etc., generating two samples for each species, seed and debris.
3. Weigh the cleaned seed and the debris separately on a sensitive scale. The weight unit used can be grams or grains, or whatever the scale reads.
4. Divide the seed weight by the sum of the seed weight and the debris weight and multiply by 100 to give percent of the original sample that is seed.
5. Thus: with 15 grams of seeds plus 80 grams of debris, the percent seeds is 15.8%: 15/(15+80) * 100
6. Record this percentage on the species list and go on to the next species.
7. When making the final seed mix, adjust the amount of each species to account for its purity.
8. With a little experience, it may be possible to “estimate” the purity by simple visual inspections.

High accuracy is not needed in this work.

Seed collecting dates for savanna species arranged by date of collection
Latin Common Collecting dates
Geranium maculatum Wild geranium June
Polemonium reptans Jacob's ladder June
Sanguinaria canadensis Blood root June
Viola pedata Bird's foot violet June
Silene antirrhina Sleepy catchfly Late-June
Aquilegia canadensis Wild columbine June-July
Actaea rubra Red baneberry July
Dodecatheon meadia Shooting star July
Lobelia spicata Pale spiked lobelia July
Osmorhiza longistylis Smooth sweet cicely July-Aug
Elymus hystrix Bottlebrush grass Aug
Taenidia integerrima Yellow pimpernel Aug
Zizia aurea Golden Alexander Aug
Actaea alba White baneberry Mid-late August
Cryptotaenia canadensis Honewort Late-Aug
Thalictrum dasycarpum Purple meadow-rue Aug-early Sept
Arisaema triphyllum Jack-in-the-pulpit Aug-Sept
Bromus altissimus Woodland brome Aug-Sept
Desmodium canadense Showy tick-trefoil Aug-Sept
Desmodium glutinosum Pointed tick-trefoil Aug-Sept
Elymus villosus Silky wild rye Aug-Sept
Anemone virginiana Tall anemone Aug-Oct
Agalinis sp Giant false foxglove Sept
Aralia racemosa Spikenard Sept
Phryma leptostachya Lopseed Sept
Polygonatum biflorum Smooth Solomon's seal Sept
Smilacina racemosa False Solomon's seal Sept
Allium cernuum Nodding wild onion Mid-Sept
Eupatorium purpureum Purple joe-pye weed Mid-Sept
Lobelia siphilitica Great blue lobelia Mid-Sept
Anaphalis margaritacea Pearly everlasting Late-Sept
Ceanothus americanus New Jersey tea Late-Sept
Cirsium altissimum Woodland thistle Late-Sept
Elymus riparius Woodland rye Late-Sept
Eupatorium sessilifolium Woodland boneset Late-Sept
Agastache nepetoides Yellow giant hyssop Sept-Oct
Agastache scrophulariaefolia Purple giant hyssop Sept-Oct
Hieracium kalmii Canada hawkweed Sept-Oct
Hypericum pyramidatum Great St. John's wort Sept-Oct
Rudbeckia hirta Black-eyed Susan Sept-Oct
Aureolaria grandiflora Yellow false foxglove Early-Oct
Campanula americana American (tall) bellflower Early-Oct
Smilax herbacea herbacea Carrion flower Early-Oct
Asclepias exaltata Poke milkweed Oct
Asclepias purpurascens Purple milkweed Oct
Triosteum perfoliatum Early horse gentian (Tinker's Oct
Rudbeckia triloba Brown-eyed Susan Mid-Oct
Aster laevis Smooth blue aster Late-Oct
Aster sagittifolius Arrow-leaved aster Late-Oct
Aster lateriflorus Side flowering aster Late Oct-Nov
Lobelia inflata Indian tobacco Late Oct-Nov
Prenanthes alba Lion's foot Late Oct-Nov
Solidago flexicaulis Zig zag goldenrod Late Oct-Nov
Solidago ulmifolia Elm-leaved goldenrod Late Oct-Nov
 
Seed collecting dates for savanna species, by Latin name
Latin Common Collecting dates
Actaea alba White baneberry Mid-late August
Actaea rubra Red baneberry July
Agalinis sp Giant false foxglove Sept
Agastache nepetoides Yellow giant hyssop Sept-Oct
Agastache scrophulariaefolia Purple giant hyssop Sept-Oct
Allium cernuum Nodding wild onion Mid-Sept
Anaphalis margaritacea Pearly (sweet) everlasting ?? Late-Sept
Anemone virginiana Tall anemone Aug-Oct
Aquilegia canadensis Wild columbine June-July
Aralia racemosa Spikenard Sept
Arisaema triphyllum Jack-in-the-pulpit Aug-Sept
Asclepias exaltata Poke milkweed Oct
Asclepias purpurascens Purple milkweed Oct
Aster laevis Smooth blue aster Late-Oct
Aster lateriflorus Side flowering aster Late-Oct/Early-Nov
Aster sagittifolius Arrow-leaved aster Late-Oct
Aureolaria grandiflora Yellow false foxglove Early-Oct
Bromus altissimus Woodland brome Aug-Sept
Campanula americana American (tall) bellflower Early-Oct
Ceanothus americanus New Jersey tea Late-Sept
Cirsium altissimum Woodland thistle Late-Sept
Cryptotaenia canadensis Honewort Late-Aug
Desmodium canadense Showy tick-trefoil Aug-Sept
Desmodium glutinosum Pointed tick-trefoil Aug-Sept
Dodecatheon meadia Shooting star July
Elymus hystrix Bottlebrush grass Aug
Elymus riparius Woodland rye Late-Sept
Elymus villosus Silky wild rye Aug-Sept
Eupatorium purpureum Purple joe-pye weed Mid-Sept
Eupatorium sessilifolium Woodland boneset Late-Sept
Geranium maculatum Wild geranium June
Hieracium kalmii Canada hawkweed Sept-Oct
Hypericum pyramidatum Great St. John's wort Sept-Oct
Lobelia inflata Indian tobacco Early-Nov
Lobelia siphilitica Great blue lobelia Mid-Sept
Lobelia spicata Pale spiked lobelia July
Osmorhiza longistylis Smooth sweet cicely July-Aug
Phryma leptostachya Lopseed Sept
Polemonium reptans Jacob's ladder June
Polygonatum biflorum Smooth Solomon's seal Sept
Prenanthes alba Lion's foot Oct-Nov
Rudbeckia hirta Black-eyed Susan Sept-Oct
Rudbeckia triloba Brown-eyed Susan Mid-Oct
Sanguinaria canadensis Blood root June
Silene antirrhina Sleepy catchfly Late-June
Smilacina racemosa False Solomon's seal Sept
Smilax herbacea herbacea Carrion flower Early-Oct
Solidago flexicaulis Zig zag goldenrod Late Oct-Nov
Solidago ulmifolia Elm-leaved goldenrod Late Oct-Nov
Taenidia integerrima Yellow pimpernel Aug
Thalictrum dasycarpum Purple meadow-rue Aug-early Sept
Triosteum perfoliatum Early horse gentian (Tinker's Oct
Viola pedata Bird's foot violet June
Zizia aurea Golden Alexander Aug
 
Packard, Stephen and Mutel, Cornelia F. (editors). 1997. The Tallgrass Restoration Handbook, for Prairies, Savannas, and Woodlands. Island Press, Washington, D.C.
Kurtz, Carl. 2001. A Practical Guide to Prairie Reconstruction. University of Iowa Press, Iowa City, IA.
Packard, Stephen. 1007. Interseeding. pp. 163-191 in Packard, Stephen and Mutel, Cornelia F. (editors). 1997. The Tallgrass Restoration Handbook, for Prairies, Savannas, and Woodlands. Island Press, Washington, D.C.

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