SEEDING RATES - WHAT'S BEST?

What's the seeding rate?, is always one of the first questions asked. It depends on who you talk to. For the most part there are excepted standards, some of those based on science and mathematical calculations, some based on experience but there are all too many based on the "if a little bit is good, a lot is better" method.
Seeding rates are always expressed as pounds per acre, either as bulk or pure live seed. When buying your seed you put your trust into what you are told, the trouble is you don't know what method was used to make the recommendation - science, experience or cover the ground with seed. You might not give that a second thought, but you should.

Seeding rates which are based upon science determine the number of seeds per pound then calculate the ideal number of seeds per square foot. Experience takes what science has determined and accounts for local factors including weather, soil condition and type, species growth characteristics and use and management. The "mulch it with seed" method ignores both in favor of some misperceived value or values.

When you know the number of seeds per square foot you can get an idea of plant density. Plant density is important because it affects the health and vigor of the plant. Plantings which are too dense and overcrowded compete for food and water, resulting in poor root development and weak plants making them susceptible to a number of problems. Drought stress, water stress, weed invasion, poor root structure, disease and fungal vulnerability are just some of the problems of an overcrowded stand.

Critical area seedings, areas in which healthy grass stands are most important, are frequently subject to the ignorance of overseeding. Time after time it happens, and for the most part it is because somewhere, someone in the past has said, "If a planting planted at 24 pounds holds the soil, and since it is really important I get a stand here, I'll plant 48 pounds." The result was, since they did get a stand, henceforth everyone who follows uses 48 pounds and doesn't question it. Let me describe to you an overseeding scenario. In this scenario I will use fescue.

I'm writing the specifications to reseed a highway construction project. I have a 3:1 slope that needs to be seeded. The purpose of the planting is to stop erosion and stabilize the slope. In addition I don't want to have to mechanically control weeds (a 3:1 slope is potentially dangerous for a tractor and manual labor is too expensive) nor do I want to have to chemically control weeds (chemicals and the environment, public relations, etc.). My technical guide says since it is a 3:1 slope it must have extra protection above what we normally plant on lesser slopes or level ground. The requirement is 48 pounds per acre because the previous manual stated 48 pounds and the one before that said 48 pounds and someone before that used 48 pounds because they thought "if 24 works, 48 will be better."

A seeding contractor, whose responsibility is to get the grass up and growing, plants 48 pounds because he is required to, though he knows better. He won't get paid if he doesn't follow the specifications. The contractor fertilizes and mulches the planting, it sprouts and a thick stand is established. The grass seed takes advantage of that initial fertilization and everything looks great. The planting looks good and performs well initially. Eventually competition between the plants stress them and the root systems don't develop to the extent they should. The sod becomes weak and weeds invade. Small riverlets begin to form on the slope because of the weakened sod. In addition, because the root system is not healthy and as deep in the ground as it should be, the slope begins to slump and huge sections slide down hill as a result of heavy rains. The Highway Department now has several options, ignore it and wonder why it was seeded at all, repair the damage and reseed at required rates only to do it over in the future, fertilize and water to maintain health and vigor or adjust their seeding rates and/or vegetative cover.

In the preceding paragraphs you probably thought I was just on a soap box but I know you can drive down highways anywhere in America and see what I just described. Next trip you take, see if I'm not right.

Why did that scenario just described, happen? Science tells me that there are 227,000 seeds per pound of tall fescue seed. When planted at a rate of 48 pounds per acre there are 249.6 seeds per square foot. Experience tells me that is too many seeds per square foot. In perspective, to make it easier to understand, that is 1.73 seeds per square inch. To give you an idea of how thick the seed is, an area the size of this sheet of paper would contain 166.75 seeds. I'm sure with that density you can imagine how much competition there will be between the plants, and without subsequent fertilizer and water the vigor of the plants will diminish. In an area in which it was most important for a healthy and vigorous stand of grass, with our objectives to preserve the slope, erosion control and reduce maintenance, we have actually done just the opposite. Yes, seeding rates are important.

How do you know what the right rates are? Well, there are no hard and fast rules. Your experience on your property will help determine seeding rates for you. In the meantime there are some guidelines to follow which at least get you in the ballpark and let you check someone else's recommendation to see if it is outrageous. Remember my statement, "experience considers the use?"

Experience provides these relative associations for either warm season or cool season grasses. Wildlife uses require the lowest seeding rates, forage production higher (about 50% higher) and critical areas the highest, usually about 100% more than wildlife uses. I know you're saying, that's what you just warned about not doing in the example above. You're right, but I didn't say to start with a rate that was too high to begin with. With the exception of high maintenance areas, (lawns, golf courses, etc.) cool season grasses should not exceed 100 seeds per square foot. Warm season grasses should not exceed 50 seeds per square foot. In my opinion most cool season plantings need to be in the 35 to 60 range, most warm season plantings in the 20 to 50 range.

I commonly recommend 4 - 6 PLS pounds of native grass seed per acre for wildlife purposes, 6 - 8 for forage and 8 - 10 for critical areas. This really represents a compromise between what I think is really necessary and what is required to get a stand in a reasonable amount of time. If I weren't concerned about the establishment period I would plant much lower rates.

Obviously with forage or critical areas, establishment time is a major consideration, but typically wildlife uses it is not. I would actually prefer to plant 4 to 5 PLS pounds for wildlife, even lower when using switchgrass. Using Table 1 as reference, lets look at some seeding rates.

If I were to plant 4 PLS pounds of switchgrass I would have 35.72 seeds per square foot. (389,000 x 4 = 1,556,000. 1,556,000/43,560 = 35.72. This could also be calculated by using the number of seeds per square foot per pound. 8.93 x 4 = 35.72) Although this number falls within the range I established it is a little high for my liking. I want switchgrass closer to 20 seeds per square foot.

Most of you aren't planting pure stands though, at least I hope not if any of my previous newsletters have had any impact. A mixture of 2 pounds big blue, 2 pounds indiangrass, 1 pound little blue and 1 pound sideoats grama, a total of 6 PLS pounds would plant 25.9 seeds per square foot. At that seeding rate there would be nearly 17 (16.8) seeds in an area the size of this sheet of paper. (Compare that to the earlier example of 166.75.)

To find out how much a mix plants, multiply the seeding rate of the individual grass by the number of seeds per square foot per pound. Repeat the process for each species in the mix and add their totals.

The greatest temptation for overseeding is critical areas. Resist temptation, you will just be aggravating the very problem you are trying to prevent. Use the information provided in Table 1 to check your seeding rates. They should be in line with the recommendations I have outlined above.

TABLE 1 - SELECTED LIST OF SEEDS PER POUND
SPECIES SEEDS/LB SEEDS/FT²/#
REDTOP
BIG BLUESTEM
LITTLE BLUESTEM
SIDEOATS GRAMA
SMOOTH BROME
ORCHARDGRASS
TALL FESCUE
SWITCHGRASS
TIMOTHY
KOREAN LESPEDESA
PARTRIDGE PEA
TICKCLOVER
ALSIKE CLOVER
RED CLOVER 4,990,000
165,000
260,000
191,000
136,000
654,000
227,000
389,000
1,230,000
225,000
64,000
200,000
700,000
275,000 114.6
3.8
5.9
4.4
3.1
15
5.2
8.9
28.2
5.2
1.5
4.6
16.1
6.3