How to Extend a Lawn in Autumn
The best time to sow grass seed for optimal germination is early to mid-fall (6 to 8 weeks prior to the first hard freeze of the season in your area)․ Here in Tennessee‚ that's somewhere between late August and mid-September in the west and central part of the state‚ and up to two weeks earlier if you live in the mountains near the east border․ The soil is still warm enough for grass seed germination‚ air temperatures have cooled at night‚ and you are not fighting the heat and drought stress that kills many attempts at spring seeding․
Why Fall Beats Spring for This Project
The temperature of the soil‚ not the air‚ controls the germination of the grass seed‚ with soil temperatures in Tennessee in September averaging between 65 to 70 degree F (18 to 21 degree C)‚ perfect to encourage cool season turf establishment․ Weeds are also going dormant in fall‚ so your new grass won't be competing with crabgrass and other summer annuals․ You get 10-12 weeks of growth before your grass goes dormant for winter‚ plenty of time for seedlings to develop a proper root system before the first summer they have to tolerate begins․
Planning the Extension
Walk the area you want to expand into‚ and keeping in mind that an area which is sunny at noon might be deep shade at 4pm‚ after the trees leaf out․ If you are thinking of expanding late summer‚ take a look back at the space in June and July․
A soil test is more critical than most people realize‚ and can be obtained from the University of Tennessee Extension office for a nominal fee‚ which is well worth it․ Due to the natural limestone of Middle Tennessee‚ Tennessee soils are more alkaline than most other East and West Tennessee soils‚ which are more acidic․ Grass grows best in a soil with a pH of about 6․0 to 7․0․ Outside that range grass seed will not germinate even in a well-watered soil․ Calcium carbonate (lime) raises soil pH and sulfur lowers it․ A soil test will tell you how much of either to use‚ given in a per 1000 square foot range․
Depending on your location‚ there are different considerations․ Tall fescue is basically the workhorse grass for most of Tennessee because it tolerates the hot and humid summers and the occasional cold snap‚ and it stays green longer into fall and winter than most other choices․ Kentucky bluegrass grows well in the cooler areas to the east‚ but is prone to disease in the hot‚ humid areas of Middle and West Tennessee․ If you are expanding your lawn area and plan to blend your lawn with new grass‚ use the same species․ Mixing patches of fescue grass with bluegrass will create a clumpy‚ uneven lawn‚ visible from the street․
Site Preparation
Remove all of the grass‚ weeds‚ roots and rocks from the extension area․ If there is existing turf that is to be removed to regrade the area‚ this removal can be expedited by the use of a sod cutter‚ rather than digging․
After soil tests are back‚ till the top 4 to 6 inches of soil‚ amending as needed․ If your soil is heavy clay (as is the case with many yards in Middle Tennessee)‚ it is useful to add some compost or well-aged manure․ Clay is dense and poorly draining‚ so the grass roots require as much air as moisture․ If you incorporate 2 to 3 inches of quality compost into the entire extension site‚ you'll see deeper roots by the next summer․
Grade around the house so that water drains from the building‚ and does not pond in low spots․ A slope of 1 inch per 8 feet (1․2 cm in 2․4 m) on grass is sufficient and not noticeable․ Lightly rake and roll with a lawn roller until the soil is firm‚ not compact․ The earth is not too hard for roots if you can push a screwdriver through the first couple of inches with your arm․
Seeding Versus Sod
Less expensive than sod‚ seeding allows you to match or improve the existing grass type‚ but with some wait․ Apply the recommended rate of seed; overseeding is wasteful whereas underseeding leaves holes for weeds․ A drop spreader or broadcast spreader can spread more evenly than hand-sowing․ The area can be lightly raked to cover the seed in the upper quarter-inch of soil‚ and then a light straw mulch can be spread on top to prevent moisture loss and discourage birds from digging up seeds․
Once or twice daily‚ water lightly‚ keeping the upper 1 inch (2․5 cm) of soil moist but not soggy or puddled․ Germination typically occurs 7 to 14 days after seeding fescue‚ and when the grass reaches 2 inches (51 mm)‚ water every other day․ When the grass is at mowing height (3 or 3․5 inches)‚ water the lawn normally (1 inch/week)․
Sod gives you an instant lawn․ It is good to use if you want to stabilize a slope instantly or are extending right before an event․ TN Nursery also sells perennial groundcovers and native plants․ These are great for the border of a newly extended lawn where it will meet garden beds․ If your extension must meet garden beds‚ lay sod within 24 hours of delivery‚ staggering seams like a brick wall and watering immediately after installation․ For the first two weeks water every day to prevent the edges drying and shrinking․
First-Year Care
Do not mow new grass until it is three inches tall‚ and do not mow more than one-third of the blade height in any one mowing․ In seeded areas‚ this is usually 3-4 weeks after the grass has germinated․
In the meantime‚ use a starter fertilizer high in phosphorus at planting․ Then apply a balanced fertilizer in fall (6 to 8 weeks after planting); do not fertilize again until spring․ Fall application of nitrogen stimulates top growth just when the plant needs to concentrate all its energy on rooting for winter survival․
If possible‚ keep foot traffic off of the new area throughout the winter․ Frozen grass broken by frost is brittle and breaks apart easily․ Also‚ walking on dormant grass can compact the turf and slow down the root development․ However‚ when the turf perks up again when the warm weather rolls around‚ the good fall-established extension should blend in well with the rest of the turf and you'll have spared yourself the stress and the increased chance of failure that comes with trying to establish a cool season grass in the Tennessee summer․
