What to do, what to do, about fall seeding…

Published: August 30, 2012

The spring of 2012 was about six weeks ahead of itself compared to most years. Most folks felt we never had a winter this year, moisture been looking good to excessive in many areas early on, and we had one of the most beautiful springs in years. Our final heavy rainfall in Columbia in late April was the hardest seen at my home place ever. The small creek that runs through my property went out of its banks higher than I have ever seen in 35 years. Trees were eroded out of its banks and a sizable foot bridge over that creek was swept away, disappearing forever. After that, someone turned the switch off and one of the driest seasons ever began to change the appearance of Missouri’s landscapes.

You may not realize how precious a resource like water can be until you experience a year of weather like the one we are having. Records have been broken since 1895 in many cases. If we look at the May-June precipitation chart from 1895 to present, we can see that 2012 is right there with 1936 and 1901 for the lowest precipitation total over the months that normally provide the highest precipitation totals. It’s no wonder that things look as they do.

If you couple this with the high temperature data (Number of days above = 100°F), we truly begin to see how precious water can be; not only for plants, but for human consumption as well. For those of you keeping track, the number of days above 100 for Columbia, MO was approaching the 1954 mark in late July; however as of August 7th that count sits at 19 days.

Along with the lack of precipitation and high temperatures, another factor in the 2012 season that played a huge role in the demise of turfgrasses is the evapotranspiration (ET) rate. This is the amount of water loss on a daily basis due to evaporation from the soil and transpiration from the plant. Who would have thought that ET rates during May of 2012 would rival ET rates typically seen in late July or early August? Warm temperatures, low humidity, and sunny/breezy days have provided daily ET rates between 0.2 and 0.3 inches. A more impressive way to think about this is to consider that 2 to 3 inches of water was being loss every 10 days resulting in dormancy of our turfgrasses and lawns. We were just not able to keep up with standard recommendations of applying 1 to 1.5 inches of irrigation per week. We generally have no concerns about lawns remaining dormant for four to five weeks; however this year lawns have remained dormant now for eight to ten weeks. My mower has sat in my garage for most of the summer without use.

Many homeowners can expect to have severe thinning or total loss of their lawns. Many will be very surprised on how much will come back once sufficient rainfall occurs. With Isaac moving up through the Gulf and now pushing through New Orleans, our next best opportunity for that slow, steady rainfall comes to us on Labor Day weekend. Let’s hope.

So now, we are facing that time of the year when lawns need to be renovated or over-seeded. The questions have been: When should we start? Should we aerate? What about the continued drought and warm weather? What about all the weeds? How do we go about it? The remainder of this article will try to answer these questions and perhaps any questions you may have as well.

As you look across your lawn, you can quickly decide just how much damage has occurred. Individual plants can be pulled from the soil and inspected to see if any green plant tissue remains in the center or crown of the plant. Any amount of green tissue means that plant has the potential to regrow with sufficient water or rainfall. Some areas of the lawn will look totally brown and crispy and dead (usually full sun areas, hilltops or berms), but there is always potential for regrowth if viable plants remain. Other areas will be more obvious for regrowth. You can still see some green tissue in the canopy and these areas exist more so in the shaded areas of a lawn.

After inspection of the lawn, homeowners can get a feel for how much work lies ahead. Determine the square footage that needs to be renovated. This number then determines the amount of seed and fertilizer needed to do the job. Once all of this is known, then we can address the other questions that may arise. Recommendations are being made to purchase seed as soon as possible due to shortages and higher prices.

When should we start: Traditionally, cool-season lawn renovations should occur in the first two weeks of September. Labor Day weekend has always been a good starting date. Seeding in the fall is usually best when we have some soil moisture in place; however this year soil moisture in the top ¼ to ½ inch of soil is very scarce. Some areas of the state have received some spotty showers and may be OK to get started. Others may not. If irrigation is an option, then this time frame is still excellent timing for renovation and over-seeding. Just keep in mind that seed requires light and frequent watering for germination and growth. If the fall continues to be dry, then watering will become hard work to keep that lawn alive. If irrigation is not an option, then seeding may need to be delayed two to three weeks in hopes of receiving some regular rainfalls. Seeding lawns can occur up to October 10th for Missouri, but again the optimum timing is the first two weeks of September.

Should we aerate: Aeration has always been an accepted method prior to over-seeding. Aeration in several directions helps to alleviate soil compaction and provides passages for air, water and nutrients to enter the root zone. Applications of fertilizer after aeration will move nutrients immediately into the root zone of your lawn. It also provides better seed/soil contact for over-seeding by dragging and crumbling soil plugs, spreading soil over seed. Here’s the problem. Aeration requires soil moisture in order to pull a nice soil plug from the soil. Lack of rainfall will make aeration impossible. Dry, compacted soils will not allow the hollow tines of the aerator to penetrate the soil surface. One option is to irrigate prior to aeration and over-seeding. But once again, keep in mind that once the seed is down, irrigation will be required for germination and growth. If irrigation is not an option, then aeration will need to be delayed until later in the fall or spring. The benefits of aeration will be well worth the effort when this practice can be provided. Aeration equipment can be found at local rental stores or garden centers. Machines that pull a ½ inch diameter plug three to four inches deep on four inch centers do an excellent job.

Power rakes or de-thatching machines are also pieces of equipment to prepare seedbeds prior to over-seeding. This equipment can also be rented and provides an excellent means of breaking up soil cores from aeration. This creates a perfect situation for dropping seed into a lawn, therefore improving seed/soil contact. Some power rakes have a seed hopper on top of the unit dropping and working seed into the soil surface all in one pass.

In extreme situations where the entire lawn needs to be renovated, tilling may be the best means of starting over and preparing a seedbed. This provides the best seed/soil contact and breaks up any compacted soils up to the tillage depth. A four-inch tillage depth is sufficient.

What about continued drought and warm weather: As already stated, once seed is down, irrigation will need to be provided on a light and frequent schedule for at least the first 7 to 10 days for seed germination. The weather will then determine if irrigation will continue to maintain grow-in. Tall fescue requires 7 to 10 days for germination, while Kentucky bluegrass requires 10 to 14 days. These are the critical time frames for these species to germinate. Warm weather during germination is usually not a factor other than drying out soil surfaces. Therefore the light and frequent watering will keep the surface moist, but not overly wet. Wet conditions with warm weather will promote turfgrass diseases during establishment. Dark soils indicate sufficient moisture, shiny soils indicate too much water.

What about all the weeds: Many weeds are considered warm season weeds and when turfgrasses are dormant, weeds still prevail and grow. Many summer annual weeds such as crabgrass, goosegrass, and spurge are not a major concern since they are annuals. Practices such as aeration and power raking will damage annual weeds sufficiently to reduce competition. There is usually no need to spray weeds this late in the season since they are annuals and October frost is just around the corner. Perennials, like dandelion, can be sprayed but will require a 3 to 4 week wait before seeding turfgrasses can take place. Sometimes it is best to wait on weed control and take advantage of planting grasses during that optimum time frame.

How do we go about it: First, pull a representative soil sample and obtain a soil test for fertilizer recommendations. Knowing which nutrients are sufficient and which ones are deficient will determine optimum fertilizer needs. Soil pH is also important to know and a pH range of 6.5 to 6.8 is excellent for turf establishment. Any lime requirements to raise pH will be specified on the soil test results. Having this information in hand prior to seeding can save you time and money when trying to establish a lawn. Fertilizer and lime can be applied prior to any seedbed preparation. Starter fertilizers (e.g. 10-24-18) have always been recommended at a rate of 1 lb of nitrogen per 1,000 square feet at time of seeding; but more recently, starter fertilizer applications have proven best when applied 10 to 14 days after seeding or when the grass is at that seedling stage. All fertilizer and lime requirements should be based on a soil test.

Preparation of the site includes the removal of any debris such as rocks and a visual inspection to make sure the grade or slope of your landscape is adequate for good surface drainage. Holes from rock removal or low water holding pockets need to be filled in to insure proper drainage. Poorly drained areas are detrimental to maintaining healthy turf.

When seeding, it is important to have good seed/soil contact to improve seed germination. Aeration, power raking or tillage is the means to prepare a good seedbed as already discussed. When tilling the soil, straw will be needed to prevent erosion and mulch the soil at a rate of one bale per 1,000 square feet. Aeration and power raking do not require straw or mulch.

Turf-type tall fescues can be seeded around 6 to 7 pounds per 1,000 square feet. Seeding rates for Kentucky bluegrass should be about 2 to 3 pounds per 1,000 square feet. Mixtures of tall fescue with Kentucky bluegrass should be seeded at 6 to 8 pounds per 1,000 square feet. Seed applications following tillage or power raking should be raked in lightly to help cover the seed with soil. Use of a light roller will also improve seed/soil contact and germination.

The final step to a successful lawn renovation is proper watering. The first two weeks after seeding are the most critical. Until the seed germinates and starts to put down a root, seed can wash away very easily. You should keep the soil surface moist, not wet. Do not let seed dry out once it starts to germinate. On warm, windy days with lower humidity, it may require several light waters a day to keep the surface moist. Always avoid puddles and runoff.

In a season such as this one, successful renovation and over-seeding are important to provide the competition needed against many weeds. If you can get started in early September, you should be mowing your new lawn by late fall. Additional fertilizer applications can be made one month following the application of the starter fertilizer. These fertilizer applications can be made with something similar to an 18-5-9 and applied at a rate of 1 lb of nitrogen per 1,000 square feet.

One final question you probably have is, “what do we plant?” Several blends and mixtures do exist for homeowners to select from. Farm co-ops, garden centers at the major box stores, and some local seed house can be excellent sources for grass seed. Some of those recommended for Missouri include the following:

With this you should be well on your way to a full lawn recovery and back to mowing that lawn again. Hopefully, cooler temperatures and rainfall will come sooner than later and let’s hope Isaac brings Missouri some much needed relief.