Sod or seed?
Sod gives you a finished lawn in a day and holds soil on slopes right away, but costs several times more than seed. Seed is cheapest and offers the widest choice of grass varieties, but it needs steady watering for a few weeks and a season to fill in.
How much sod do I need?
Add the lawn area in square feet and add 5% for trimming (10% for curved beds and lots of edges). Divide by the pallet size: most farms ship pallets of about 400–500 sq ft, with 450 the most common. Slabs are usually 16" x 24" (2.67 sq ft); rolls are often 2' x 5' (10 sq ft). Sod is perishable, so lay it the day it arrives.
How much grass seed do I need?
Seeding rates are given in pounds per 1,000 sq ft and depend on seed size. University extension ranges for a new lawn: Kentucky bluegrass 2–3 lb, bluegrass with 10–20% perennial ryegrass 3–4 lb, turf-type tall fescue 6–8 lb, perennial ryegrass 4–6 lb, fine fescue 3–5 lb, hulled bermudagrass ½–1 lb and zoysia ½–3 lb. The planner uses the middle of each range. Overseeding a thin lawn takes about half the new-lawn rate.
When to plant
Cool-season grasses (bluegrass, fescue, ryegrass) do best seeded in late summer to early fall, when the soil is warm and the air is cool; spring is the second choice. Warm-season grasses (bermuda, zoysia) should be seeded in late spring or early summer. Sod can go down any time the ground isn't frozen, as long as you can water it.
Prepare the soil
Remove the old turf, loosen the top few inches, rake out stones and level low spots with topsoil. Apply a starter fertilizer at the bag rate. After seeding, a light layer of straw — about one bale per 1,000 sq ft — holds moisture and keeps seed from washing away.
Sources: Penn State Extension, Purdue Extension, University of Tennessee Extension. Watering it next? Lay out the heads with the sprinkler layout planner.