Lawn Terms, in Plain English
Every term the lawn world assumes you know — defined in a sentence or two, linked to the calculator that does the math.
- N-P-K
- The three numbers on every fertilizer bag: percent nitrogen (green growth), phosphorus (roots), potassium (stress tolerance) by weight. A 24-0-4 bag is 24% nitrogen. Related tool →
- Pounds of N per 1,000 sq ft
- How all turf feeding is measured — the standard application is 0.75–1.0 lb of actual nitrogen per 1,000 square feet, whatever bag it comes from. Related tool →
- Pre-emergent
- Herbicide that stops weed seeds from establishing (it doesn't kill existing weeds). Timing is everything: down before soil hits ~55°F in spring for crabgrass. Blocks grass seed too.
- Post-emergent
- Herbicide for weeds that already exist. Selective ones kill broadleaf weeds but spare grass; non-selective (glyphosate) kills everything green it touches. Related tool →
- Overseeding
- Spreading seed into an existing lawn to thicken it — done at about half the new-lawn seed rate, classically in early fall. Related tool →
- Cool-season grass
- Bluegrass, fescues, ryegrass — thrive in spring/fall, struggle in deep summer. The northern-US default. Seed them in early fall.
- Warm-season grass
- Bermuda, zoysia, St. Augustine, centipede — love heat, go brown and dormant after frost. The southern default. Plant in late spring.
- One-third rule
- Never remove more than a third of the grass blade in one mow. Sets your mowing frequency from your kept height. Related tool →
- Soil pH
- How acidic your soil is. Turf wants 6.0–7.0; below that, fertilizer stops working efficiently. Lime raises it, sulfur lowers it, a soil test measures it. Related tool →
- Soil test
- A ~$15 lab analysis (state extension offices run them) of your soil's pH and nutrients — the difference between feeding what's missing and guessing.
- Thatch
- The spongy layer of dead stems and roots between grass and soil. Under half an inch is healthy mulch; over that blocks water and invites pests — time to dethatch.
- Core aeration
- Pulling plugs of soil out of the lawn to relieve compaction so air, water, and roots move again. Fall for cool-season lawns, late spring for warm-season.
- Topdressing
- Spreading a thin layer (¼–½ inch) of compost or soil over the lawn — levels small bumps and feeds the soil biology. Related tool →
- Growing degree days (GDD)
- Accumulated warmth used to time treatments scientifically — how pros know when crabgrass will germinate without guessing from the calendar.
- Tuna-can test
- Straight-sided cans catch sprinkler water for 15 minutes; the measured depth converts to your system's true output — the key to watering by inches, not vibes. Related tool →
- Deep and infrequent watering
- The watering philosophy that builds drought-proof lawns: fewer sessions that soak deep, training roots downward — vs daily sprinkles that keep roots shallow. Related tool →
- Scalping
- Mowing so short the blades are gone and stems/soil show. Stresses grass, invites weeds, and browns the lawn — the most common self-inflicted lawn wound. Related tool →
- Starter fertilizer
- Higher-phosphorus fertilizer for new seed and sod (roots first). One of the few times the middle N-P-K number should be big. Related tool →
- Slow-release nitrogen
- Coated or organic nitrogen that feeds over 6–10 weeks instead of days — costs more, burns less, feeds steadier. The label says what % is slow.
- Broadcast vs drop spreader
- Broadcast throws granules in a swath (fast, most common); drop releases straight down (precise near beds). Either works — calibration matters more than type. Related tool →
- Sod
- Farm-grown grass delivered as rolls of living carpet. Instant lawn at roughly 10× the cost of seed. Related tool →
- Dormancy
- Grass going brown to survive stress (summer drought for cool-season, winter for warm-season). Dormant isn't dead — it greens back when conditions return.
Missing a term? The homepage lists every tool by category — most definitions live where the math happens.