If you've ever sowed grass seed that was washed downhill after a heavy rain or gobbled up by hungry birds, using a slit seeder may be the answer. This piece of equipment, which looks similar to a lawn mower, is typically available for rent at your local garden center or tool rental store. As you push it, a slit seeder slices the soil into shallow furrows and deposits grass seeds into the slits. Some machines roll or tamp the soil as a finishing touch to ensure good soil-to-seed contact. The seeds stay in place when it rains, and they're tucked in the soil just out of beak's reach from birds.
Prior to using the slit seeder, the first important step is to prep your lawn. Skimping on this step by going straight to slit seeding could mean a waste of time and money. The soil where you'll sow your new grass seeds has to be able to sustain the healthy growth of your future lawn.
Overseeding an Existing Lawn
Slit seeders excel at "overseeding," or sowing seeds into an existing lawn. There are three primary reasons for overseeding:
- To thicken up a sparse, wispy lawn.
- To fill in bare patches in your lawn.
- To sow cool-season turf grass seeds into an existing warm-season lawn so you can enjoy a green yard during the winter.
The quality of your new lawn depends heavily on several preparatory steps:
Step 1: Test the Soil
If the soil has deficient or excessive nutrients, the new grass may struggle to become established after you sow the seed. And if the pH is not adjusted to a level that's suitable for the particular type of grass you're growing, the roots won't be able to absorb nutrients properly. If you're not skilled in interpreting the results from a purchased soil-test kit, you can have the soil tested at a laboratory or your closest county extension office.
Typically, a pH of between 5.5 and 6.5 is optimal for most turf grass types.
Step 2: Get Rid of Weeds
Before you add new grass seeds to your lawn, now is the time to get rid of the weeds. Determine what type of weeds you have -- grassy weeds, broadleaf weeds or sedges. Choose a selective herbicide that kills the type weeds you have without killing the grass, and follow all label recommendations and cautions, particularly the required interval to wait before you can safely seed your lawn. If you don't have a lot of weeds, you can hand-pull them, but make sure you remove the roots, too.
Step 3: Water Your Lawn
Soak the lawn thoroughly -- to a depth of 6 to 8 inches. Let the surface dry just enough so you can dethatch and aerate.
Step 4: Dethatch Your Lawn
Thatch is a buildup of organic matter between the grass and the soil surface, commonly composed of grass stems (including rhizomes and stolons), crowns and roots. If enough of this layer exists, it can strangle new grass growth. You can use a stiff rake to remove the thatch or a vertical mower -- also called a power rake,.
Step 5: Aerate Your Lawn
Use a core aerator to loosen compacted soil. This machine removes small plugs of soil, opening up pockets in your lawn that allow air and water to move more easily to plant roots.
You can rent vertical mowers and core aerators at your local garden center or hardware store.
Step 6: Fertilize Your Lawn
As a rule of thumb, apply 1/2 pound of nitrogen per 1,000 square feet of lawn. Apply phosphorus and potassium based on soil-test recommendations. Adjust the pH, if necessary, by adding lime, according to soil-test recommendations.
Starting from Scratch
If your lawn is in such poor shape that you're ready to start all over with it, use the same steps for overseeding an existing lawn, but replace Step 2 above with these steps:
Step 1: Remove all Grass and Weeds
Use a ready-to-use nonselective herbicide -- one that kills or damages every plant it touches -- or plow or till your lawn to remove all grass and weeds. Typically, you spray a nonselective herbicide, such as one that contains glyphosate, until all surfaces of a plant are wet, but not dripping. Follow all label recommendations and cautions, as products and formulations vary. Use the herbicide when conditions aren't windy and rain isn't expected. Most formulas show results anywhere between 24 hours and one week. Keep children and pets out of the area until the herbicide is completely dry.
Choose a product without residual action, which could kill newly germinating grass. Avoid products that include names or descriptions such as "extended control" and "preventer" -- these can prevent grasses from growing for several months.
Step 2: Rake, Level and Grade
Rake your lawn smooth by removing all dead plants, rocks and debris. Grade the soil away from your home's foundation, and level all low spots where water can collect and rot grass roots.
Using a Slit Seeder
Step 1: Fill the Hopper
A slit seeder has a hopper, which is a receptacle for the grass seeds. Typically, the hopper is at the rear of the machine because the cutting blades are at the front to slice into the ground before the seeds are released.
Step 2: Set the Seed Flow Rate
According to the seed bag instructions or the chart that is typically included with a machine rental, set the dial to control the seed flow rate. This rate depends on the type of grass you're seeding and how thickly it can be seeded.
Step 3: Set the Blade Depth
Sow the grass seeds at the proper depth, following the manufacturer's directions. For example, if the directions on the seed bag note to sow the seeds at a depth of 1/2 inch, set the blade depth on the slit seeder, typically by moving a lever to the correct measurement mark.
Step 4: Make Two Passes
Push the slit seeder in one direction across your entire lawn, and then push it in the perpendicular direction, making two full passes across the area.
Follow-up is critical after you sow the seeds.
- Keep the seeds moist but not soggy by making frequent but light sprinklings. In hot weather, this may mean watering twice a day.
Don't let the soil around newly sown seeds dry out, or the seeds may not germinate.
- Wait until the new grass is 3 inches high before mowing it for the first time. Set your mower blade to remove only 1 inch at a time for the first few mowings. Gradually increase the blade height until you reach 3 inches.
- Six weeks after the seeds germinate, apply nitrogen fertilizer at the rate of 1 pound per 1,000 square feet.
- Wear suitable clothing, including closed-toe shoes or boots, safety glasses and hearing protection.
- Keep a good grip on the slit seeder on rocky terrain and dips in the lawn so the machine doesn't tip over. Do not use the equipment on grades greater than 20 percent.
- Keep children and pets away from the area where you're working, and check blind corners, such as around trees and shrubs, before steering the machine forward.
- Follow all make- and model-specific instructions in the operator's manual.