David M. Kopec, Extension Turfgrass Specialist

Springtime means the frosts and/or snow is gone, and people are itchy about getting outside. This usually means some lawn maintenance and spring cleaning. For now, we'll avoid the spring cleaning and stay with just the lawn. This issue addresses partial re-seeding of cool season grass lawns such as Kentucky bluegrass, ryegrass and tall fescue.

You may find that some areas of the lawn have died over the winter, and that the grass is dead as a doornail. The dead grass may appear as a tan carpet, or just as straggles of dead and/or weak patches of grass.

The dead patches of grass may be the result of any of the following conditions:

1) Winter dry-out (winter desiccation). Although the grass is "wet" in the spring, the grass may have dried out from cold winds – especially if there was no snow cover.

2) Too much snow cover. Plants in the lawn around Flagstaff may have died if snow was piled and stayed too long at the edge of the driveway and by the sides of walkways. Look for these kinds of patterns of dead or weak grass – and you probably have found out why. This occurs especially in cases where there was rain before or after snow melts. The "dead" spots appear as the "last of the snow" melts.

3) Salt damage. This occurs adjacent to walkways and where runoff occurs from salted driveways, and on the edge of salted driveways.

4) Heavily shaded areas the summer before.

5) Wet, soggy areas from gutter downspouts.

There are many more reasons why the lawn may have dead patches, or be very weak.

Grass Renovation:

Choose the right time!

It can be "too early" to re-seed the lawn. While the seed will not die, it may just sit until the ground gets warmer. The trick is to put the seed down so it will come up quickly. For Flagstaff, apply the seed in mid-May. Try to renovate cool season grasses when the daytime temperatures are about 75º. This is safe for all areas which grow cool season grasses as year-round turfs.

Is too much seed too much of a good thing?

You bet it is. Putting down too much seed can be disastrous for the lawn. Overapplication of seed can and will result in a spindly looking turf in which plants remain in the "single stalk stage." This turf will be weak and struggle through most of the summer, and most likely die in July or August. You must ask yourself just how much of the Spring Renovation of the lawn is needed? Are you simply replanting dead spots, or is the entire lawn weak?

For Reseeding Dead Spots:

1) Remove grassy thatch IF present. Use a de-thatch rake to thin out the dead grass – if it is really thick and completely covers the soil. If the dead grass is thin, and the soil is open, this step can be skipped.

2) Loosen the soil and promote drainage. Lightly rake the soil, so the seed can be buried by re-raking after the seed is dropped. Work the soil in several directions. The rake should go about 1.0 inch deep. If the soil is wet, it will clump and pull up in large chunks. Wait until it dries out some. It is highly recommended to stick a pitch-fork or a cob-fork down as deep as you can. This will promote good drainage. Seed that "sits" in water-soaked soil will drown!

Apply the seed to the dead areas. You can either use a lawn spreader, or sprinkle the seed carefully by hand. Carefully means: do not apply too much seed. The more soil that is exposed and "rakeable," the less seed you will need in reality.

When seeding dead areas (patches) by "eye," try to have the following coverage:

Grass # seeds per Square Inch

Tall Fescue 6 - 8
Perennial ryegrass 10 - 12
Kentucky bluegrass 20
Fine fescues 10 - 12

If seeding a three-way lawn seed mixture (Kentucky blue, Fine leaf fescue, ryegrass), make sure you mix up the seed by hand. There is a big difference in seed size. Also, make note of the fact that the bluegrass seed will be overlooked when you hand sprinkle mixtures that have the larger seeder ryegrass and fescues with it.

Rake the seed in the soil so as to cover the seed in the top1/4" or so. Lightly tamp the seed with the back of a shovel or rake. If the soil is too wet, you can compact the soil, which can decrease germination. On lawns in which the entire lawn is thin, you can re-seed over the entire lawn. The actual seeding rate depends on how much of the seed applied will actually reach the soil. Re-seeding rates can be high based on percent of existing cover. This is because a large amount of the seed will fall on existing plants, and probably not reach the soil.

Preparing the lawn if it is to be entirely re-seeded:

First things first!

See if the lawn has any thatch in it. Lawns which had (have) a lot of Kentucky bluegrass make the most thatch. If the thatch is 1/2 inch or more, you can take advantage of this time to thin the thatch and expose soil at the same time.

Rent a verticutter, a lawn-rent-o-thin, or de-thatcher machine from the garden center. Set the blades on the machine so that they are about touching the bottom of the green grass shoot. Don't set it down to the soil level – it will get there on its own!

Walk across the lawn in multiple directions: go at least three, preferably four directions! Each time you "make a pass," the machine will sink more into the lawn. The more you sink, the more thatch you bring up. Slow and steady wins the race here! Avoid ploughing and deep ripping the soil itself.

You will end up with a lot of biomass that needs to be removed. Either rake it off, or use a lawn mower with a bag catcher. You will empty the bag many times. Make enough "shallow passes" until loose soil is showing. Make a final decision if you need to make one more pass at (only) a slightly deeper depth to loosen the soil. If the soil is very compacted (typical of lawn soils which have a high silt or clay content), you can also aerify after the vertical mowing procedure prescribed above.

Rent a lawn aerifier which has 5/8" or 3/4" hollow core tines. This will take out plugs which fall out on the lawn. Do this (you guessed it) in two directions. Then chop up the cores by running over them with the verticutter set just slightly lower than the actual mowing height. This brings more soil to the surface and opens up the soil. Roots will fill the holes before you know it.

The following seed rates can be observed when re-seeding existing lawns in the Spring: 
Amount of Seed Based on
Percent of Bare Ground Showing
Grass Type 50% 40% 30% 20%

Tall Fescue 8 8 5 4
Perennial Rye 10 10 8 6
KBG 3 3 3 2

Mixture: 6 5 4 4
Rye 25%
Fine Fescue 25%
KBG 50%

For starting a new lawn from scratch, (100% bare ground) use the same seed
rate as the 50% renovation seed rate.

Seed can be applied across the entire lawn by using a drop spreader, or a centrifugal – rotary spreader. Drop spreaders avoid the application of seed in unwanted areas. Centrifugal spreaders are used effectively on large lawns. Drop spreaders are used in smaller areas, and seed only goes where the spreader itself goes!

Pre-weigh the seed on a scale, or "guestimate" the amount of seed in the bag or pail. The container of seed bag is sold by weight. A 50 lb. bag of seed emptied into 4 even piles is about 12 lbs. of seed per pile.

Measure the yard by multiplying the width by length of the yard. Then, take one-third of the total seed to be used and apply it by only slightly opening the spreader opening. Walk as many times across the turf as necessary to apply the total seed amount. Walk the spreader in several directions, otherwise the lawn will end up with corn rows, or patchy, uneven blocks.

When 50% of the soil in the lawn is exposed soil, rake the new seed in. When less than 50% of the lawn soil is exposed, it is necessary to drag or brush the seed in. An inverted carpet weighted with a 2x10 board dragged across the yard in multiple directions will push the seed down into the soil. You can topdress with composted manure. Apply no more than a 1/8" dusting! When possible, follow by rolling the lawn with a weighted roller. All equipment mentioned is available from lawn/landscape rental centers.

If the entire lawn is going to be re-seeded, you can apply a pre-emergence herbicide right at the time you are seeding. There is one special pre-emergence product that will stop many weeds from germinating, and let the lawn seed still come up. The product is called TUPERSAN. The active ingredient is siduron. Follow the label directions carefully. Do not use other pre-emergence herbicides. They will also kill the turf seeds. When using TUPERSAN, apply 10% more seed than the recommended amount. Follow all other seed establishment items as described previously. Just make sure you apply the TUPERSAN after the seed is sown, raked and rolled. If you are not sure or comfortable with applying the TUPERSAN granules, then skip this part. Too much product will ruin the new seeds.

Irrigate the lawn once/twice a day to keep the seeds moist. Do not let them dry out. Ryegrass will germinate in 6-10 days. Tall fescue and KBG will take longer. Let the lawn dry out for 1-2 days before mowing. Cut the lawn at 2-1/2 inches. Fertilize the lawn with a high phosphate fertilizer (16-20-0) at 5.0 lbs. of fertilizer per 1,000 square feet of lawn, and water it in.

Change the water schedule to every second or third day, based on weather conditions. You're off and running!