When seed production is your goal, good cropland is preferable to use for the establishment of seed production plots, so long as concerted efforts are made to maintain genetic diversity. Soils should be loamy, or sandy if irrigation and fertilization are options. Deep soil free from topographic variation and stones will make mechanical operations much easier and the crop more uniform in its development.

       More important than soils are the weed populations and history of a field being considered for seed production. Ideally, a field would be completely free of introduced species before being employed in native plant seed production, but this may not be an option. Consequently, it is strongly recommended that fields be fallowed for two years and subject to rigorous weed control prior to stand establishment. Locations infested with noxious weeds such as quackgrass or Canada thistle must be especially avoided. These perennial weeds tend to be abundant in former hay fields and pastures, so land that was previously used for cereals or other annual crops is generally preferable. Due to difficulty in identifying grass species in seedling and vegetative phases, it is imperative that no native grass seed crops be established where perennial grass weeds such as quackgrass are present.

Seed increase plots and seed production fields can be established in three main ways (see expandable photos below): transplanting greenhouse-started plants; manually sowing single rows; or mechanically sowing multiple (usually closely-spaced) rows. In all cases, provisions should be made for convenient weed control and harvesting. The first option (left photo, below) is usually employed when starter seed is in short supply or its germination is unreliable. Seedlings are started in a greenhouse and then transplanted as individual seedlings out into garden plots, usually arranged in rows for ease of weed control and harvesting. Seedlings can be started in open flats, or in containers; tree seedling containers such as StyroblocksTM can often be scavenged from tree nurseries and have the advantage of keeping root systems of neighbouring plants separate. A container-grown root system forms a “plug” that is easily transplanted. Seed can be started in any sterile greenhouse rooting or potting medium, consisting of some combination of peat moss and vermiculite, perlite, loam or sand. Seeds and seedlings are typically watered one or more times per day, fertilized once or twice a week with an all-purpose (high N-P-K plus S and micronutrients) plant food, and temperatures are monitored and venting adjusted to make sure that seeds and seedlings aren’t heat-stressed.

Methods of seed increase plot or seed production field establishment:
     
Transplanting greenhouse-grown plugs | Single-row hand seeder | Tractor-drawn seed drill.

       Seed production plots or fields can also be started from seed, either in single or closely paired rows, or in tight stands (usually on a larger scale). Seed generally needs to be well cleaned and detached from any appendages (fluff and awns) or mixed with an inert carrier (such as cracked wheat, cat litter, or fertilizer) so it will flow well in the seeding machinery. A hand-pushed single-row seeder (middle photo, above) does the job for most small-scale production areas. Sowing depth and density are easily adjusted, and peat moss, sawdust or loose soil can be manually scattered over surface-sown seeds. Rows are typically spaced 80 to 100 cm apart in order to allow room for weed control (e.g., by rototilling) and maintenance access, and will also promote more vigorous growth than in dense stands. Rolls of plastic or paper mulch between rows can be an effective weed deterrent, but manual weeding within the rows will usually still be required.

       Mechanical sowing (right photo, above) is also an option for most species. Specialized precision equipment suitable for small-scale plot production is manufactured by companies such as KubotaTM, AlmacoTM, and WintersteigerTM, but older small farm equipment will often be adequate for sowing, cultivating, and harvesting. Seed drills should be equipped with press wheels or the ground should be packed after seeding, except on heavy clay soils. The depth of seeding should never be greater than twice the longest diameter of the seed being sown; this means the small-seeded species are just spread on the surface and then lightly pressed into the loose soil. The use of a carrier to bulk up volumes and to improve seed flow in seed drills may be necessary (especially with the chaffy and hairy species). Seed carriers can consist of cracked or roasted grain, vermiculite, and cat litter. Commercial fertilizer has also been used as a carrier, but is not recommended because of toxicity effects of having high concentrations of fertilizers (and their salts) immediately adjacent to germinating seeds, and because of corrosive effects on machinery.

       Where feasible, irrigation during crop establishment is a good idea. Most developing seedlings will not tolerate drying, and this is the most vulnerable stage in seed crop stand management. Irrigation can continue until the flowers are ready for pollination recommend that irrigation be stopped then and during seed ripening, although irrigation may resume temporarily during early seed development. In our experience, Rhizobium innoculant to stimulate the formation of nitrogen-fixing nodules in legumes is unnecessary on agricultural soils.

Weeding is usually the main stand maintenance activity. Manual weeding by pulling or hoeing is the norm, with mulching or rototilling between rows. Once plants are well established and are mature in size, careful placement of deep straw or other mulches can greatly reduce the need for weeding, which is very labour-intensive. Sometimes selective herbicides can be used: for example, dicotyledon weeds can be killed by broadleaf herbicides such as 2,4-D or BanvelTM (active ingredient dicamba) if the crop is a grass. Although grasses and sedges are not killed by these chemicals, they can sometimes inhibit seed production, and these chemicals are all somewhat toxic to animals and humans. Spot-spraying with glyphosate (e.g., RoundupTM) is another option, utilizing a backpack sprayer or spray bottle. A shrouded nozzle or a sheet of rigid plastic or plywood can serve as a baffle to protect adjacent crop plants. If a young stand is being over-run with weeds, one can sometimes “cup” all crop plants with upside-down plastic containers, and then broadcast-spray all weeds with glyphosate or other broad-spectrum systemic herbicide. Even large fields of native plants should still be walked to remove non-crop species, especially the exotic and noxious species that produce seed that would contaminate the seed crop.

       To promote stand vigour and seed production, it is generally recommended that seed production plots and fields be fertilized. The appropriate fertilizer formulation and its rate of application will need to be adjusted depending on the species and the condition of the soil; soil testing should be conducted to determine deficiencies. For example, forb plots should be fertilized with a balanced fertilizer when plots are first established and annually thereafter. Grasses do not need excessive nitrogen (N) as this will encourage vegetative growth and lower seed yield. Nitrogen-fixing plants may not need nitrogen but will need other nutrients. Though high N supplements may be called for in the soil test results, this should only be done while the plants are in an early vegetative phase; higher ratios of phosphorus (P) and potassium (K) to N should be utilized in early to middle summer to promote seed set and filling.

       With the exception of Collinsia parviflora, all 31 species evaluated in our 5-year program are perennials. It appears that some species (e.g., Arnica and Aster spp.) may be long lived, but others (e.g., Festuca occidentalis, and Achillea millefolium) have a relatively short life span (under 3 years) as seed producers. Weed control, fertilization, and stand rejuvenation through clipping and thatch removal can prolong stand life, but not indefinitely.

       Mowing grass plots immediately after harvest and removing any post-harvest residue from forb plots are recommended to help reduce disease and insect problems. This procedure also increases light and heat to the plant root crowns at the beginning of the next growing season. Remove weeds routinely before they go to seed in order to keep plots weed free, and the reservoir of weed seeds in the soil will eventually be depleted.

       Where specific information is available for particular species, variations to these stand management recommendations in our manual in individualized accounts for 31 species. Much still needs to be learned about stand maintenance and the optimal timing for stand replacement. Growers are urged to try various management regimes (especially related to fertilization routines) and to keep records of stand maintenance practices, so this information can provide improved guidance for producers in the future.

Wild plants, by definition, have not been selected for uniformity of ripening time, which has been one of the first steps in the domestication of many of man’s crop plants. As a result, the seed in stands with broad genetic diversity typically ripens over a long period of time, with some seed heads over-ripe and losing their seeds to the ground before seed on other plants is ripe yet. So the careful timing of harvest, and approaches to repeatedly and selectively harvesting a stand, are important for the protection of genetic diversity during the production of native plant seed. Given the threat that seed stocks might be contaminated with exotic species, it is also a good idea to rogue out all undesired seed heads (of weeds and other non-crop species, and those that might be diseased) from the stand prior to harvest to avoid seedlot contamination.

       Depending on the species, harvesting may entail the stripping of seeds from seed stalks in the field, or the entire removal of those seed stalks and heads for threshing. In both approaches, the challenge is to glean ripe seeds efficiently from the plants without scattering the valuable seed to the ground and losing it. The harvesting methods described here are primarily manual and small-scale mechanical approaches. Sharp hand sickles are very effective for harvesting most grasses and sedges (left photo, below), while sharp clippers work well for other species. A scythe may also be appropriate for some grasses. Seeds can be harvested selectively as they ripen but this is time-consuming and eliminates any possibility of mechanical harvest. Placing plastic between rows early in the season will not only help to control weeds but also permits harvest of the seed crop when the bulk of it is ripe. Seeds that ripen early will drop onto the plastic and can be later vacuumed up, so long as they are not contaminated with weed seeds: it is a good idea to sweep or vacuum the plastic to remove dirt, debris and other contaminants just before the crop starts ripening.

Methods of harvesting seed from increase plots or production fields:
   
Using hand sickles | Motorized seed stripper.

       Small seed increase plots do not warrant the expense of combine harvesters, though seed production fields >0.2 ha might be harvested with such equipment if available. Recommended settings for the rotation speed of the combine cylinder head in rotations per minute (rpm) and concave spacing (in mm) are therefore provided with the individual species descriptions in our manual. Mechanical harvesting is especially suitable for most of the large-seeded grass and sedge species, and where large quantities of seed are being harvested on a regular basis. For plots intermediate in size, a hand-held seed stripper (right photo, above) can be used (see www.prairiehabitats.com). While this method is especially useful for harvesting some seed from wild stands, we found it was not efficient for salvaging all the seed being grown in plots, because much of the seed was scattered by the stripper strings rather than being scooped into the hopper. Therefore, if using a seed stripper, make sure there is cleanly swept plastic between the rows so that scattered seed can be salvaged with a vacuum or broom.

       If one has access to electricity or a generator, a shop vacuum works extremely well for harvesting the species with fluffy seeds. A modified gas leaf blower is also available at a reasonable price, but its suction is not as good as that of a shop vacuum. There are also industrial vacuums and sweepers (such as various ToroTM Flay-O-Vac and Rake-O-Vac models) that can be pulled behind a tractor, but these are expensive. Modifications that combine sweeping and vacuuming action (also expensive; e.g., the Woodward Flail-VacTM system; see www.ag-renewal.com) may represent the ideal compromise for harvesting field-grown wild seed. Flail-Vac heads range in width from 1.2 m to 3.6 m, and are mounted on front-end loader arms fitted to all-terrain vehicles (ATVs) or tractors. Technology that combines sweeper and vacuum action is generally flexible enough to be applied to a variety of species, and can be used repeatedly on the same stand for selective harvesting as seed ripens.

Curing harvested seed on the stalk prior to threshing:
   
Swaths for combining or threshing | Spread in a warehouse .

       As mentioned above, seeds of wild and genetically diverse cultivated plants typically do not ripen uniformly, so this must be taken into account when harvesting. When using manual and vacuum harvesting methods, repeated passes of the seed production area every few days will allow most seed to be collected rather than lost. For seeds that are held more tightly to seed heads, it is often most practical to cut the entire crop at one time, and to then dry or cure it under warm dry conditions, thereby allowing much of the green or soft seed to fully ripen before threshing. Hand-clipping, sicklebar mowing, or swathing should be done before a significant amount of ripe seed falls and while some seed is still green or soft. Seeds can be efficiently dried in the sun if the weather co-operates. This step essentially allows the younger seeds to “catch up” in their process of maturation without losing all of the more mature seed. On a large scale, this is done by swathing the stand before threshing or combining it (left photo, above); on a smaller scale, sheaves (bundles) of seed stalks can be spread to cure on large tarpaulins or plastic sheets, or on clean concrete floors in the shelter of a warehouse or shed (right photo, above). Losses to mice and voles can be a problem, so mouse traps may need to be set, and drying times should be kept to a minimum (generally a few days to a couple weeks). Once dried, seed should be threshed immediately. If immediate threshing is not possible, seed heads or seed stalks should be stored as sheaves, or loosely in paper or breathable seed sacks, so that any remaining moisture can escape and the seed won’t mold.

Like harvesting, threshing and cleaning can be done by a range of manual and mechanized approaches. Old farm machinery can provide an economical means of harvesting, threshing and cleaning native plant seed, though modifications and relatively large quantities of seed are typically required. Seed is usually somewhat threshed (removed from seed stalks and seed heads) in the harvesting process, and more seed usually falls off during handling. It is important to salvage this seed, which is made easier by working on clean, sweepable concrete surfaces. Further seed removal can be done by hand-stripping, or by a variety of mechanical beaters or flails. For very small quantities, placing seed heads in a closed container with a hard rubber ball and shaking vigorously can serve to dislodge seeds; this can also be done in conjunction with small-scale seed cleaning using soil sieves.

       Symbios Research & Restoration uses two machines for mechanized threshing, both mounted on stationary stands and powered by 373 to 736 watt (½ to 1.0 hp) electric motors. One is a custom-made rotary flail, consisting of 10-cm lengths of bolted pipes between four steel disks (12 cm radius) mounted on an axle and housed in a cowling that directs seed downwards (see photo at right). Seed stalks are held by hand in large clusters, with the seed heads inserted into the flail until all or most seeds are removed by the beating action. Care must be taken that heads are never inserted so far that they get wrapped around the axle, and that hands are not drawn into the machine (wearing strong, loose work gloves and eye protection is essential).

       If the resulting seed stock still contains a number of full or partial seed heads with seeds attached (as often happens for some grass species), seed may be run through a second machine called a rethresher. A rethresher is like a miniature combine harvester, consisting of concave-grooved bars attached to a heavy flywheel that can be run at different rotations per minute (rpm); the one we utilize was salvaged from an old Massey HarrisTM combine. Seed is removed from stems when the machine lines up the stems and seeds longitudinally, and abrades them against small plates protruding perpendicularly from the housing. Seed species require different optimal widths for the space between the rotating bars and the fixed plates (“concave spacing”), and in the optimal rpm at which to operate the machine. Where known, these recommended specifications are provided for individual species in our manual, and these settings are assumed to be good preliminary estimates for full-scale combine harvesters as well. The seed heads and stalks left after threshing can be bundled or baled to serve as a straw mulch for weed control in seed production plots of the same species, or for erosion control on bare soils at revegetation sites.

       The objectives of seed cleaning are to separate pure seed from chaff and other vegetative debris, to remove the seed of any contaminating species, and (sometimes) to remove most of the small unfilled seed that is unlikely to germinate. While vegetative debris does not functionally inhibit the use of the seed in revegetation, this debris often makes seed lots more bulky and difficult to handle because the seed supply won’t flow easily through machinery. Seed cleaning is generally done by one or a combination of methods: sieving by size and shape, and/or separating by buoyancy in an air stream.

       We utilize a variety of brass soil sieves for manual cleaning of small quantities of seed, and for the final “finishing” step of cleaning some large seed lots. The primary cleaning operation can be done by a small fanning mill, consisting of two or more large flat shaker screens, and an adjustable stream of air generated by a large fan, all powered by an electric motor (see photo at right). As with hand sieving, screens are carefully selected by matching the size and shape of their apertures to match the upper and lower sizes of viable seeds of the crop species. Consequently our manual reports, for each species, seed dimensions and recommended specifications for the “top screen” (which excludes seeds and debris larger than the crop seed) and for the “bottom screen” (which lets seeds and debris smaller than the crop seed fall through). Sometimes a preliminary screen is utilized too, in order to exclude larger stems, leaves, and other debris. The air stream of a fanning mill is adjusted by setting the rotation of the fan at different speeds, and/or by adjusting a baffle to damp down the wind created by the fan. Trial and error for each individual seed lot is required in order for the air stream to remove chaff and dust but not crop seed. A general guideline is that all non-crop seeds and as much debris as possible should be removed by the cleaning process, without losing more than 5% of the crop species.

       A custom-made vacuum airflow cleaner was used for some seed lots as the final cleaning step in the Symbios program (see photo at right). Many versions of such machines exist, generally connected to a commercially available vacuum cleaner that is controlled by an adjustable rheostat (a “dimmer switch”). Seed is gradually released from a hopper, and passed over an upward-flowing air stream and over one or more baffles so that heavy contaminants fall straight down, the desired seed is pushed or pulled over the first baffle, and dust and chaff continues on over a second baffle. Each machine will vary in its power, distances, baffle configuration, and the adjustments possible, so settings generally have to be made on a trial and error basis with each seed lot. As with all seed cleaning procedures, the operator has to carefully monitor that the crop is properly separated from both small and large contaminants, without losing too much of the valuable seed to the “reject” stream. The rejected material from all cleaning processes is commonly referred to as “screenings,” and can be useful as a mulch for revegetation projects, so long as it is sure to be free of weed seeds.

       Clean seed can be stored in sacks, bags, or plastic buckets and tubs (see photo at right). It is important that seed be protected from insects and rodents that might consume or contaminate it. If well cured, dry, and stored in cool dry conditions, seed from most of the species with which we have worked has proven to remain viable in storage for at least five years. Each container should be clearly labeled according to a unique seedlot identifier, denoting the species, grower or field, year of production, and any other particulars. The weight or volume of seed should be recorded, and an inventory database maintained to record additions and withdrawals of seed stocks.

       In order to prepare precise seeding prescriptions, it is important to know the viability and purity of each seed lot being used. Seed lot purity simply denotes what proportion of the bulk weight consists of pure mature seeds, as determined from weight measurements of several random samples. Seed viability is usually determined from germination tests on several samples of those mature seeds, generally under standard moist warm conditions in a laboratory. These determinations can be made by the seed grower, or (more often) by specialized testing labs or seed brokerage houses. The results of seed lot tests conducted by licensed testing labs are reported in “certificates of analysis.” The product of purity and viability percentages give the “pure live seed” (PLS) content of a seed lot, important for the accurate calculation of seeding rates (see web page on using seed for revegetation and restoration). Purity analysis of several samples is also important in order to check for the presence of seeds of any non-crop species. Seeds of some domesticated and weed species subsequently can be separated by re-cleaning the seed lot, or else the seed lot can be used for establishing agricultural pastures or hay fields. Under no circumstances should seed lots known to contain noxious weeds be used for ecosystem restoration purposes or introduced into largely wild, uncontaminated landscapes.

       There is currently no requirement under the Canada Seed Act to use certified seed for purposes of revegetation or ecological restoration. There is some progress in establishing standards of germinability and purity for official certification of native plant seeds, but the many species, difficult cleaning procedures, and little trade in this material means that such progress is slow. Once such standards are in place, hopefully they will support rather than inhibit the wider production and use of native plant seed.