Lawn Care Terms Explained: NPK, Thatch, Dormancy & More

By Lawn Expert Jack, Lawn Care Researcher  |  August 4, 2026  |  Updated: August 4, 2026

Fertilizer and Soil Chemistry

N-P-K

The three numbers on every fertilizer bag: nitrogen, phosphate and potash, as a percentage of total weight. Nitrogen drives leaf growth and colour, phosphorus drives root development, potassium supports stress and disease tolerance. A 25-0-5 is 25 percent nitrogen, no phosphate, 5 percent potash.

Actual nitrogen

The nitrogen itself, as opposed to the weight of the bag. Every extension recommendation is written in pounds of actual nitrogen per 1,000 square feet, and this is where most people go wrong.

Slow-release and quick-release nitrogen

Quick-release (soluble) forms are available to the plant immediately, work at low temperatures, and are used up in roughly three to four weeks. Slow-release forms break down gradually over about six to eight weeks and are far less likely to burn. Most lawn products are a blend, giving an immediate response plus a longer tail.

Starter fertilizer

A product with proportionally more phosphorus, for new seedings where root development matters most. Typical analyses are 10-10-10, 16-8-8 or 18-24-6. Applied at 0.5 to 1 lb of nitrogen per 1,000 sq ft — above about 1.5 lb it burns young turf.

Fertilizer burn

Damage caused when fertilizer sits so concentrated around the roots that it draws water back out of the plant. It shows as yellow-brown streaks following your spreader pattern. Most common in hot weather or when product is not watered in.

Soil pH

A measure of acidity from 0 to 14, with 7 neutral. Most turfgrasses do best between roughly 6.0 and 6.8. Outside that band, nutrients become progressively less available to the plant — meaning fertilizer you have already paid for does less work.

Lime and sulfur

Lime raises soil pH, sulfur lowers it. Both are slow, taking months to years for a substantial change. Neither should be applied on a schedule — only when a soil test shows a need, because excess is as harmful as deficiency.

Soil test

A laboratory analysis of pH and nutrient levels, ordered through your county extension service. It turns lime and fertilizer from guesses into decisions, and it is the cheapest genuinely useful purchase in lawn care. Full process in our soil testing guide.

Grass and Growth

Cool-season and warm-season grasses

The fundamental division. Cool-season species — tall fescue, Kentucky bluegrass, perennial ryegrass, fine fescue — grow hardest in spring and autumn and struggle in summer heat. Warm-season species — bermudagrass, zoysiagrass, St. Augustinegrass, centipedegrass — thrive in heat and go dormant after frost. Almost every other recommendation depends on which you have. See our grass types hub.

Dormancy

A survival state where the grass stops growing and loses colour, but stays alive. Warm-season grasses go dormant after frost and turn tan through winter. Cool-season grasses go semi-dormant in summer heat and drought, turning brown and recovering when cooler weather returns.

Green-up

The point in spring when a dormant warm-season lawn resumes growth and regains colour. Highly variable — often April near the coast, as late as mid-May further inland. It is the trigger for the first feeding of the year, and feeding before it risks frost damage to new growth.

Cultivar, blend and mixture

A cultivar is a named variety within a species. A blend is several cultivars of the same species. A mixture is more than one species. Blending three or four Kentucky bluegrass cultivars is standard practice because the species has little genetic variation within a cultivar, so blending is what buys disease resilience.

Rhizome, stolon and bunch-type

How a grass spreads. Rhizomes are underground stems, stolons are above-ground runners; both let a grass fill gaps on its own. Bunch-type grasses like perennial ryegrass grow in clumps and cannot spread into a bare patch — which is why a bunch-type lawn needs overseeding rather than self-repair.

Pure live seed (PLS)

Purity multiplied by percent germination, divided by 100 — the proportion of a bag that will actually grow. Both figures are on the legally required seed label. A bag at 85 percent purity and 60 percent germination is 51 percent PLS; one at 99 and 90 is 89 percent. Compare bags on this, not on price.

Transition zone

The band across the middle of the country where both grass families can survive but neither is fully comfortable. Summers are too hot for cool-season grasses and winters too cold for warm-season ones, which makes it the hardest region to manage. See our transition zone guide.

Soil and Structure

Thatch

A tightly intermingled layer of partially decomposed grass stems and roots, sitting between the green growth and the soil surface. Under about half an inch it is normal and beneficial. Above that it restricts water, fertilizer and pesticide movement into the soil, and roots growing into it dry out.

Compaction

Soil pressed dense enough that air, water and nutrients cannot move through it and roots cannot penetrate. Concentrated in walking paths, gates and play areas rather than spread evenly. Test it by pushing a screwdriver into moist soil — if it stops short or takes real force, that area is compacted.

Topsoil and subsoil

Topsoil is the upper, biologically active layer where roots do most of their work; subsoil lies beneath and is far poorer. Quality turf wants a minimum of 4 to 6 inches of settled topsoil. On new builds the two are often mixed or the topsoil stripped, which is why so many new-build lawns decline in their second season.

Root zone

The depth of soil where the roots actually operate — typically 4 to 6 inches for cool-season lawns in summer. It is the depth you are trying to wet when watering, and the depth into which phosphorus and lime must be incorporated before planting.

Organic matter

Decomposed plant and animal material in the soil. It improves both extremes: helping sandy soils hold water and nutrients, and improving drainage and aeration in clay. Compost and sphagnum peat are the usual amendments.

Practices and Equipment

Core aeration

Pulling small plugs of soil out of the lawn to relieve compaction and let air, water and nutrients reach the roots. The cores are left on the surface to break down. It is a corrective procedure, not annual maintenance — do it where the screwdriver test says the soil is compacted, during active growth.

Dethatching, power raking and verticutting

Three names for mechanically removing thatch. Power rakes use spring tines that pull thatch to the surface. Vertical mowers (verticutters) use fixed blades that cut grooves through the thatch and into the soil, and prepare a better seedbed. Warranted only above about half an inch of thatch.

Overseeding

Sowing seed into an existing lawn to thicken it, without killing what is already there. Distinct from establishment, which starts from bare soil, and from renovation, which usually involves killing the existing vegetation first. See overseeding.

Sodding, sprigging, plugging and stolonizing

Topdressing

Spreading a thin layer of soil — about a quarter to half an inch — over growing turf. It hastens thatch decay, smooths shallow depressions, and is usually done straight after aerating. Never bury the grass: at least three quarters of the plant should still see light.

Scalping

Cutting so low that stems and soil are exposed, either by mowing too short or by mowing an uneven surface. It stalls root growth and opens the soil to weed seed. The deliberate exception is the low pre-green-up cut on dormant bermudagrass in late winter.

The one-third rule

Never remove more than a third of the blade height in a single mowing. A lawn kept at 2 inches is cut when it reaches about 3. Removing more stalls root growth and forces more frequent watering to keep the plants alive. Detail in our mowing height guide.

Deep and infrequent watering

Applying enough water to wet the whole root zone, then waiting until the lawn needs it again, rather than a little every day. It pulls roots downward and builds drought tolerance. About an inch a week including rainfall suits most established lawns — roughly 620 gallons per 1,000 square feet.

Establishment and renovation

Establishment is creating a lawn from bare soil. Renovation is repairing an existing one, either by overseeding into it or by killing the existing vegetation and reseeding. Which one you need is decided by how much of the lawn is still desirable grass — see our assessment guide.

Weeds, Pests and Control

Pre-emergent and post-emergent

A pre-emergent forms a chemical barrier at the soil surface that prevents weed seed from germinating, so it must be applied before the weeds appear. A post-emergent treats weeds that are already growing. Applying a pre-emergent after weeds emerge achieves nothing.

Selective and non-selective

Selectiveherbicides kill certain plants while leaving turfgrass unharmed — most broadleaf weed killers work this way. Non-selective products such as glyphosate kill whatever they touch, including your grass, which is why they belong to full renovations rather than spot treatment.

Broadleaf and grassy weeds

Broadleafweeds — dandelion, clover, plantain, ground ivy — have wide leaves and are usually controllable selectively. Grassy weeds such as crabgrass, nimblewill and quackgrass are grasses like your turf, which makes selective removal far harder and sometimes impossible in a home lawn.

Annual and perennial weeds

Annualscomplete their life cycle in one year and rely on seed, so pre-emergent timing controls them well — crabgrass is the classic. Perennials return from roots each year and need post-emergent treatment while actively growing, ideally in autumn when they are moving resources downward.

Indicator weed

A weed whose dominance tells you something about the site. Prostrate spurge and goosegrass suggest compaction; nutsedge and moss suggest wet ground; violets and ground ivy suggest shade. Treating the weed without addressing the condition guarantees it returns. Table of indicators in our assessment guide.

Threshold

The pest population at which treatment is justified, rather than treating on a schedule. For white grubs it is roughly 5 to 10 per square foot, and healthy unstressed turf tolerates more than stressed turf. Below threshold, a population is simply part of a functioning lawn.

Cultural control

Managing pests and weeds by changing growing conditions rather than by applying products — correct mowing height, deep watering, appropriate fertility, the right species for the site. It is slower than spraying and it is what stops the problem recurring.

Quick Index

Frequently Asked Questions

What This Means for Your Lawn

Vocabulary is not the point — being able to act on a recommendation is. Three of these terms change what you actually do this season.

• Actual nitrogen determines whether you apply the right amount of fertilizer or a fraction of it. Run any recommendation through our fertilizer calculator before you buy.
• Dormancydetermines whether a brown lawn is an emergency or a season. Check your grass type first — the answer differs completely between the two families.
• Thatch determines whether dethatching is maintenance or damage. Cut a plug and measure before renting anything.

With the vocabulary in place, the six fundamentals are the shortest route to a better lawn, and the month-by-month calendar tells you when each job belongs.

About the Author

Jack is a lawn care researcher and former landscaping crew lead with 20+ years working transition-zone turf. He writes every guide here from university extension publications and turfgrass research rather than product marketing — after learning the hard way that most of what gets passed around on job sites is backwards.

Have a question or topic suggestion? Get in touch.

Sources and further reading

• Penn State Extension — Lawn Establishment (pure live seed, blends and mixtures, starter fertilizer rates, topsoil depth)
• Penn State Extension — Renovation of Lawns (thatch definition, renovation versus establishment, selective and non-selective control)
• University of Missouri Extension — Cool-Season Grasses: Lawn Maintenance Calendar (G6705) (dormancy, thatch forming independently of clippings, topdressing depth, aeration, grub thresholds)
• University of Minnesota Extension — Fertilizing Lawns (N-P-K, slow versus quick release, fertilizer burn, pH range)
• Clemson Cooperative Extension — Lawn Establishment (HGIC 1203) (sodding, sprigging, plugging and stolonizing definitions)

Definitions here follow the usage in university extension publications rather than manufacturer marketing, which sometimes uses the same words differently. Where a term has a number attached, that number varies with grass type and region — your county extension office can narrow it. How we research and review guides is set out in our editorial policy.