AerationCreating holes in the lawn surface to relieve compaction, improve drainage, and allow air, water, and nutrients to reach grass roots. Hollow-tine aeration (removing plugs of soil) is more effective than spike aeration (pushing holes without removing material).CompactionWhen soil particles are pressed tightly together — often from heavy foot traffic, play, or vehicles — reducing the air spaces roots need to grow. Compacted lawns drain poorly, feel hard underfoot, and are prone to moss. Treat with hollow-tine aeration.Drought stressGrass under water shortage turns dull green or straw-coloured and loses its springiness — footprints remain visible for longer than usual. Most cool-season grasses go dormant rather than die; they recover with rain or irrigation. Do not fertilise drought-stressed grass.Fertiliser / lawn feedA product supplying one or more of the nutrients grass needs to grow. Sold as granules, liquid concentrate, or slow-release pellets. Spring/summer feeds are high-nitrogen for green growth; autumn feeds are low-nitrogen and high-potassium to harden grass for winter.FungicideA product applied to control fungal lawn diseases such as red thread, fusarium patch, or dollar spot. Usually applied as a liquid drench. Improving drainage and air circulation is more important long-term than repeated fungicide use.HerbicideA product that kills plants. Selective herbicides kill broadleaf weeds without harming grass. Non-selective herbicides (e.g. glyphosate) kill everything — only use where you intend to reseed or re-turf.Lawn sandA mixture of sharp sand, sulphate of ammonia (nitrogen), and sulphate of iron. Iron kills moss and some weeds; nitrogen promotes grass growth; sand opens up the soil surface. Applied in spring when moss is actively growing.NPKThe three primary plant nutrients: Nitrogen (N) for green leaf growth, Phosphorus (P) for roots, and Potassium (K) for hardiness and disease resistance. The numbers on a fertiliser bag (e.g. 20-5-10) show the percentage of each by weight.OverseedingSowing grass seed into an existing lawn without removing the turf. Used to fill bare patches, thicken thin grass, or introduce a tougher or finer grass variety. Best done in late summer or early autumn when soil is warm but rain is more reliable.pH (soil)A measure of how acidic or alkaline your soil is. Most lawn grasses prefer a slightly acidic pH of 6.0–7.0. Below 5.5, nutrients become less available and moss thrives. Raise pH with lime; lower it with acidifying fertiliser. Test soil pH with an inexpensive kit before adjusting.ScarificationUsing a mechanical or manual scarifier to remove thatch — the layer of dead organic material between the grass blades and the soil surface. Light scarification is done with a spring-tine rake; heavy scarification uses a powered machine with blades. Best done in early autumn.ThatchA layer of dead and living organic matter (grass stems, roots, debris) that builds up at the base of the grass. A thin layer (under 1 cm) is beneficial; thick thatch blocks water and nutrients, harbours disease, and makes lawns feel spongy. Removed by scarification.Top dressingSpreading a thin layer of compost, sand, or loam over the lawn surface. Improves soil structure over time, levels minor undulations, and encourages grass to tiller (spread sideways). Best applied after scarification and before overseeding.Wetting agentA product that reduces the surface tension of water so it penetrates dry or waxy soil more easily. Useful on "dry patch" areas where water runs off rather than soaking in, or on lawns recovering from drought stress.Grass types — cool-seasonGrasses that grow best in temperatures of 10–24°C — suited to the UK, Northern Europe, and similar climates. Common types: Perennial Ryegrass (hard-wearing), Fescues (fine texture, shade-tolerant), Bent grasses (fine, suited to ornamental lawns).Grass types — warm-seasonGrasses that grow best in temperatures above 20°C, going dormant and brown in winter. Common types: Bermudagrass, Zoysia, Buffalo/St. Augustine grass. Prevalent in Southern Europe, the US South, Australia, and similar climates. 