Growli glossary
Gardening terms,
in plain English.
100definitions of the words gardeners use — written so you don't need a horticulture degree to understand them.
Soil & nutrients20 terms
Compost
Compost is the dark, crumbly result of decomposed plant and food waste. It feeds soil microbes, supplies slow-release nutrients (roughly 1-1-1 NPK), and dramatically improves soil structure and water retention.
Cover crop
A cover crop is a plant grown to protect and improve soil rather than to harvest. Cover crops suppress weeds, prevent erosion, add organic matter, fix nitrogen, and feed soil biology between cash-crop seasons.
Drainage
Drainage is how quickly water moves through soil after irrigation or rain. Good drainage keeps roots from sitting in saturated soil, which is the leading cause of root rot in pots and beds.
Ericaceous (acid-loving)
Ericaceous describes plants in the heath family (Ericaceae) and other acid-loving species that need soil with a pH below 6.0 — typically 4.5 to 5.5 — to take up iron and other nutrients properly. Wrong pH causes yellowing and stunted growth.
Green manure
Green manure is a cover crop that is cut down and incorporated into the soil while still green and growing, rather than allowed to mature. The fresh plant tissue releases nitrogen and organic matter quickly as soil microbes break it down.
Leaching
Leaching is the downward movement of soluble nutrients and salts through the soil profile, washed by rain or irrigation water. It is both a problem (lost fertility) and a tool (flushing accumulated salts from container plants).
Leaf mould
Leaf mould is the dark, crumbly material left when deciduous leaves slowly break down over one to three years under fungal — not bacterial — decomposition. It is the gold-standard soil conditioner for moisture retention and seed-starting mixes.
Loam
Loam is the gardener's ideal soil texture: roughly 40% sand, 40% silt, and 20% clay. It drains well, holds moisture and nutrients, and is easy to work — the standard most growing advice assumes.
Micronutrients
Micronutrients are the trace elements plants need in tiny amounts — iron, manganese, zinc, copper, boron, molybdenum, chlorine, and nickel. Deficiencies are rare in well-composted soil but common in container plants, hydroponics, and very acid or alkaline soils.
Mulch
Mulch is a 2-4 inch layer of material spread over soil to conserve moisture, suppress weeds, and moderate temperature. Organic mulches like bark and straw also feed the soil as they break down.
Nitrogen
Nitrogen (N) is the macronutrient plants use in the largest quantity, driving leafy green growth, chlorophyll production, and overall vigour. It is the first number on every fertiliser label and the one most likely to run short mid-season.
NPK ratio
NPK ratio is the percentage of nitrogen (N), phosphorus (P), and potassium (K) in a fertilizer, printed on the label as three numbers like 10-10-10. It tells you which macronutrient dominates the mix.
Organic matter
Organic matter is the decomposing and decomposed plant and animal material in soil — compost, leaf mold, manure, root residue. Healthy garden soil contains 3-6% organic matter; topping it up is the single highest-leverage soil improvement.
Perlite
Perlite is a lightweight, white volcanic glass that has been heated until it pops like popcorn. Gardeners mix it into potting soil at 10-30% by volume to improve drainage and aeration around roots.
Phosphorus
Phosphorus (P) is the macronutrient that drives root development, flowering, and fruit set. It is the middle number on a fertiliser label and unlike nitrogen, it moves very slowly through soil — so it needs to be present where roots can reach it.
Potassium
Potassium (K) is the macronutrient that regulates water movement, stomatal opening, disease resistance, and fruit quality. It is the third number on a fertiliser label and the nutrient fruiting crops need most as they ripen.
Soil amendment
A soil amendment is any material added to soil to improve its physical or chemical properties — texture, drainage, pH, water retention, or fertility. Unlike fertilisers, which feed plants directly, amendments rebuild the soil itself.
Soil pH
Soil pH measures how acidic or alkaline your soil is on a 0-14 scale, where 7 is neutral. Most vegetables and houseplants prefer a slightly acidic range of 6.0-6.8, where nutrients are most available to roots.
Top-dressing
Top-dressing is the practice of applying a thin layer of compost, fertilizer, or mulch on top of the soil around an established plant. Worms and rain carry the nutrients down to the roots without disturbing them.
Vermiculite
Vermiculite is a heat-expanded mineral that looks like soft golden flakes and holds 3-4 times its weight in water. It is mixed into potting soil to retain moisture and nutrients near roots.
Plant biology20 terms
Air layering
Air layering is a propagation technique where roots are forced to develop on a stem still attached to the parent plant by wrapping a wounded section in damp sphagnum moss. Used for woody houseplants and shrubs that are hard to propagate from cuttings.
Callusing
Callusing is the formation of a protective layer of undifferentiated cells over a cut or wound on a plant stem. Allowing cuttings and divisions to callus for 1 to 7 days before potting reduces rot and improves rooting success.
Division (propagation)
Division is the propagation of clumping plants by splitting one mature plant into two or more sections, each with its own roots and growing points. It is the fastest, most reliable form of vegetative propagation for many perennials, grasses, and houseplants.
Dormancy
Dormancy is a plant's built-in rest period — triggered by short days, cold, or drought — when growth slows or stops and metabolism drops. Recognizing dormancy is the difference between a healthy winter pause and a "dying" plant you accidentally drown.
Etiolation
Etiolation is the pale, stretched, leggy growth a plant produces when it isn't getting enough light. Stems elongate, internodes get long, leaves get smaller and lighter, and the whole plant reaches toward the nearest window in search of more photons.
Fenestration
Fenestration is the natural splits and holes that develop in the leaves of mature Monstera and related aroids. It's a sign of maturity and good growing conditions, not damage — and it requires bright light plus a vertical support to develop fully.
Germination
Germination is the process by which a seed wakes from dormancy and grows into a seedling. It requires water, oxygen, the right temperature, and for some seeds, light or a cold period. Time from sowing to first true leaves typically ranges from 3 days (radish) to 4+ weeks (parsley).
Grafting
Grafting is the horticultural technique of joining the top of one plant (the scion) to the root system of another (the rootstock) so they grow as a single plant. It combines the best traits of both — flavour or appearance from the scion, vigour or disease resistance from the rootstock.
Internode
An internode is the segment of stem between two consecutive nodes (the points where leaves and side shoots attach). Short internodes signal a compact, well-lit plant; long, stretched internodes signal etiolation from insufficient light.
Layering (propagation)
Layering is a propagation method where a stem is encouraged to root while still attached to the parent plant — usually by pinning a flexible branch to the soil and burying part of it. The new plant is separated only after roots have formed.
Leaf axil
A leaf axil is the angle where a leaf meets the stem. Inside that crook sits an axillary bud that can grow into a new branch, flower, or sucker. Most pruning, pinching, and pollination decisions revolve around what's happening at the leaf axil.
Node
A node is the joint on a plant stem where leaves, buds, and roots emerge. The space between two nodes is called an internode. Nodes are the single most important feature when taking cuttings — no node, no roots.
Photosynthesis
Photosynthesis is the process where plants use light energy, water, and carbon dioxide to produce sugars and oxygen inside their chloroplasts. It powers virtually all plant growth and underpins almost every other gardening decision you make.
Phototropism
Phototropism is the directional growth of a plant in response to light. Shoots grow toward the light source (positive phototropism) and roots grow away (negative phototropism). The hormone auxin redistributes to the shaded side, making those cells elongate faster and the stem bend.
Propagation
Propagation is creating new plants from an existing one — through cuttings, division, layering, or seed. Most houseplants propagate easily from stem cuttings rooted in water or soil, making it the cheapest way to grow your collection.
Respiration
Respiration is the chemical process by which plants break down stored sugars to release energy for growth and maintenance — the reverse of photosynthesis. Unlike photosynthesis, it happens 24 hours a day in every living cell and consumes oxygen.
Rhizome
A rhizome is a horizontal underground stem that stores energy and sends up new shoots along its length. Ginger, ZZ plants, snake plants, irises, and bamboo all spread via rhizomes — making them easy to divide and propagate.
Root-bound
A root-bound (or pot-bound) plant has filled its container with roots, leaving little soil to hold water or nutrients. Signs include roots circling the pot, water running straight through, and stalled growth despite proper care. The fix is repotting one size up.
Stomata
Stomata are microscopic pores on the surface of leaves (mostly the underside) that open and close to let carbon dioxide in for photosynthesis and water vapour out via transpiration. Their behaviour controls how much water a plant uses.
Transpiration
Transpiration is the movement of water from a plant's roots up through the stem and out through tiny leaf pores called stomata. It cools the plant, pulls nutrients upward, and drives most of how much water your plant actually needs.
Climate & timing20 terms
Blanching
Blanching, in horticulture, is the practice of excluding light from a growing vegetable to keep its tissue pale, tender, and mild. Used on celery, leeks, endive, chicory, cauliflower, and forced rhubarb. (Not to be confused with the kitchen technique of dunking vegetables in boiling water.)
Bolting
Bolting is when a leafy or root vegetable suddenly sends up a flowering stalk and stops producing useful growth. It is triggered by day length, heat, root stress, or vernalisation — almost always a one-way trip toward bitter leaves and tough roots.
Bottom heat
Bottom heat is gentle warmth applied to the underside of a seed tray or propagation flat to keep root-zone soil temperature in the optimum range for germination and rooting. Usually delivered by an electric heat mat at 20 to 26 °C.
Chill hours
Chill hours measure the cumulative time a fruit tree spends between roughly 32°F and 45°F (0–7°C) during winter dormancy. Deciduous fruit trees like apples, peaches, and cherries need a specific minimum to break dormancy and bloom normally in spring.
Cloche
A cloche is a small, transparent cover placed over an individual plant or short row to create a miniature greenhouse effect. Traditional bell-shaped glass cloches, modern plastic tunnels, and DIY cut-bottle cloches all serve the same purpose — protecting tender plants from cold, wind, and pests.
Cold frame
A cold frame is a low, glazed, unheated box that extends the growing season by trapping solar warmth around plants. It hardens off seedlings in spring, protects salads through autumn and winter, and overwinters borderline-hardy perennials.
Day length
Day length is the number of hours between sunrise and sunset at your latitude on a given date. Many crops — onions, spinach, soybeans, strawberries — use day length, not temperature, as the cue for bulbing, flowering, or going to seed.
First frost
The first frost (or first fall frost) is the average date of the season's first freezing temperature in autumn. It ends the growing season for warm-weather crops and is the anchor date for planning final harvests, garlic planting, and cover-crop sowing.
Frost date
A frost date is the average calendar date when air temperature at your location is expected to drop to 32°F (0°C). Gardeners use two: last spring frost and first fall frost, which together define the frost-free growing window.
Growing degree days (GDD)
Growing degree days are a measure of accumulated heat above a base temperature — usually 10 °C for vegetables — used to predict when crops will reach key growth stages. Each day adds (mean daily temperature − base) GDD to the running total.
Growing season
The growing season is the stretch of days each year when conditions allow plants to actively grow — most commonly defined as the frost-free window between last spring frost and first fall frost. It ranges from about 90 days in cold climates to year-round in subtropical zones.
Harden off
Hardening off is the 7–14 day process of gradually exposing indoor-raised seedlings to outdoor conditions — sun, wind, and cooler temperatures — before transplanting. Skipping it causes leaf scorch, transplant shock, stalled growth, or outright death.
Hardiness zone
A hardiness zone is a geographic band defined by average annual minimum winter temperature. The USDA system uses 13 zones in 10°F steps; in the UK, RHS H1–H7 ratings serve a similar purpose for perennials and shrubs.
Last frost
The last frost (or last spring frost) is the average date of the final freezing temperature of spring at your location. It is the anchor date for transplanting frost-tender crops — tomatoes, peppers, basil, beans, and squash — outdoors.
Microclimate
A microclimate is a small area whose temperature, wind, humidity, or sun exposure differs noticeably from the surrounding regional climate. A south-facing brick wall, a frost pocket, or a sheltered courtyard can shift the effective hardiness zone by half a step or more.
Photoperiod
Photoperiod is a plant's response to the relative length of day and night. Short-day plants flower when nights exceed a critical length; long-day plants flower when nights are short; day-neutral plants flower based on age and temperature instead.
Row cover (floating fleece)
Row cover (also called horticultural fleece, frost fleece, or floating row cover) is a lightweight spun polypropylene fabric laid directly over crops to provide 2 to 6 °C of frost protection, insect exclusion, and wind shelter while still letting light and water through.
Shoulder season
Shoulder season is the transition window at either end of the main growing season — early spring and late autumn — when daytime warmth is enough to grow crops but night-time cold, frost risk, or short day length still restrict what is possible. Cold-hardy salads, brassicas, and root crops dominate.
Stratification
Stratification is a seed pre-treatment that simulates the conditions a seed would experience naturally before germinating in spring. Cold-moist stratification (4 to 8 weeks at 1 to 4 °C) breaks dormancy in most temperate perennial, tree, and shrub seeds.
Vernalisation
Vernalisation is the physiological cold treatment that biennial and winter-annual plants need before they can flower. Winter wheat, garlic, onions, brassicas, and many bulbs all require weeks of temperatures roughly between 0 and 10 °C to switch from vegetative to reproductive growth.
Watering & care20 terms
Bottom watering
Bottom watering is the practice of setting a potted plant in a tray of water so the roots draw moisture upward through the drainage holes, hydrating the soil evenly without wetting the foliage or crown.
Capillary action
Capillary action is the upward movement of water against gravity through narrow spaces in a porous material — soil pores, paper towels, or plant xylem. It is the physical principle behind bottom watering, self-watering pots, and the rise of water from roots to leaves.
Companion planting
Companion planting is the deliberate pairing of crops that benefit each other — through pest deterrence, pollinator attraction, nitrogen fixation, shade, or scent — to improve yield, flavour, and resilience without extra inputs.
Coppicing
Coppicing is the traditional woodland practice of cutting certain tree and shrub species back to a low stump on a regular cycle. The stump (the "stool") regrows multiple straight stems, producing a continuous, renewable harvest of poles, firewood, and craft material.
Deadheading
Deadheading is the routine removal of spent, fading, or finished flowers from an ornamental plant. Cutting blooms before they form seed redirects the plant’s energy into more flowers, longer bloom periods, and stronger overall growth.
Drainage layer (myth)
The "drainage layer" — gravel, pebbles, or broken pottery placed in the bottom of a pot — was long thought to improve drainage. Decades of soil-science research show the opposite: a drainage layer actually raises the saturated zone in the pot. Recent 2025 experiments are starting to complicate the picture, but the safer default remains: skip the gravel.
Evapotranspiration
Evapotranspiration (ET) is the combined total of water that leaves the soil by surface evaporation and water that leaves the plant through transpiration. ET is the most accurate single number for working out how much irrigation a crop or garden actually needs.
Foliar feeding
Foliar feeding is the application of dilute liquid fertiliser directly to plant leaves rather than to the soil. Nutrients are absorbed through stomata and the leaf surface. Useful as a quick top-up for minor deficiencies, but never a substitute for healthy soil.
Intercropping
Intercropping is growing two or more crops in close proximity within the same bed — typically a fast crop tucked between a slow one — to make better use of light, space, water, and time than either crop alone.
No-dig (no-till) gardening
No-dig gardening (also called no-till) leaves soil undisturbed and builds fertility from the surface down — annual compost mulches feed the soil, smother weeds, and let earthworms and fungi build structure naturally. Yields match or exceed conventional dug beds with a fraction of the labour.
Overwatering
Overwatering is the chronic condition where soil stays saturated for too long, suffocating roots and triggering rot. It is usually caused by watering too frequently, poor drainage, or oversized pots — not by giving too much water in a single session.
Pinching
Pinching is the deliberate removal of a soft growing tip — usually with thumb and forefinger — to break apical dominance, encourage lateral branching, and produce a bushier, more productive plant.
Pollarding
Pollarding is a pruning technique where the main stems of a tree are cut back to a fixed point on the trunk (the "head"), typically 2 to 4 metres above ground, on a regular cycle. Like coppicing, the tree responds with vigorous regrowth from the cut points.
Self-watering pot
A self-watering pot is a planter with a built-in water reservoir below the soil chamber, separated by a wicking platform or capillary column. The plant draws water from the reservoir as needed, smoothing out the over- and under-watering cycles of conventional pots.
Side dressing
Side dressing is the application of fertiliser to the soil alongside an established plant during the growing season. Unlike pre-plant feeding, it tops up nutrients exactly when fast-growing crops are about to need them most.
Soak and drain
Soak and drain is a top-watering technique where you water thoroughly until liquid runs freely from the drainage holes, then let the substrate dry to the appropriate depth before watering again — never on a fixed schedule.
Succession planting
Succession planting is the practice of staggering sowings of the same crop — or replacing a finished crop with the next one — so the garden produces a continuous harvest instead of a single overwhelming glut followed by an empty bed.
Topping (FIM and main-stem topping)
Topping is the removal of the main growing tip of a plant to break apical dominance and force branching from the side shoots below the cut. Common in tomato, pepper, cannabis, and basil cultivation. Distinct from (and not to be confused with) the harmful arborist practice of "tree topping."
Underwatering
Underwatering is when a plant goes too long without enough moisture, causing leaves to wilt, crisp, and curl as cells lose turgor. Mild drought stress is recoverable; chronic underwatering shrinks root systems and stunts growth long-term.
Wicking
Wicking is the use of a porous strip — usually cotton or synthetic cord — to move water from a reservoir into a pot via capillary action. The plant draws what it needs and stops, eliminating the over- and under-watering swings of conventional watering.
Pests & disease20 terms
Anthracnose
Anthracnose is a group of fungal diseases caused mainly by Colletotrichum species, producing dark, sunken, water-soaked lesions on leaves, stems, and especially fruit. Common in beans, tomatoes, cucurbits, strawberries, mangoes, and woody ornamentals during cool, wet spring and summer weather.
Aphid
Aphids are tiny pear-shaped sap-sucking insects, usually green, black, or pink, that cluster on new growth and undersides of leaves. They reproduce rapidly and excrete sticky honeydew that fuels sooty mold.
Biological control
Biological control is pest management using living organisms — predators, parasitoids, pathogens — instead of synthetic chemicals. Examples: ladybirds for aphids, Encarsia formosa parasitic wasps for whitefly, nematodes for vine weevil grubs, and Bacillus thuringiensis for caterpillars.
Blight
Blight is rapid, widespread browning, withering, and death of plant tissue caused by fungal, oomycete, or bacterial pathogens. Unlike discrete leaf spots, blights collapse large sections of leaf, stem, or flower at once.
Blossom end rot
Blossom end rot (BER) is a physiological disorder — not a disease — that causes a dark, sunken, leathery patch on the bottom (blossom end) of developing tomato, pepper, courgette, and squash fruit. It is caused by uneven calcium delivery to the fruit, almost always driven by irregular watering rather than soil calcium deficiency.
Chlorosis
Chlorosis is the yellowing of plant tissue caused by reduced chlorophyll production. Common triggers include nutrient deficiency (iron, nitrogen, magnesium, manganese), high soil pH, overwatering, root damage, and viral infection.
Damping off
Damping off is a soil-borne fungal disease that kills seedlings within days of germination, caused by Pythium, Rhizoctonia, Fusarium, and Phytophthora species. Seedlings collapse at the soil line with a pinched, water-soaked stem. Prevention is the only real cure — by the time you see symptoms, intervention is usually too late.
Honeydew
Honeydew is the sticky, sugary liquid excreted by sap-sucking insects such as aphids, scale, mealybugs, whiteflies, and some psyllids. It coats leaves and nearby surfaces and provides a substrate for sooty mold fungi.
Integrated pest management (IPM)
Integrated pest management is the EPA-recognised, environmentally-sensitive framework for pest control. It combines pest monitoring, action thresholds, prevention, biological controls, and targeted chemical sprays — used only as a last resort — to manage pests with the lowest possible risk to people, beneficial wildlife, and the environment.
Leaf spot
Leaf spot is a general term for discrete, often circular lesions on leaves caused by fungal or bacterial pathogens. Spots may be brown, black, tan, or yellow-haloed and often expand or merge in humid conditions.
Mildew
Mildew is a catch-all term for two distinct fungal-type diseases: powdery mildew (white surface dusting that thrives in dry warm air) and downy mildew (yellow leaf-top patches with grey-purple fuzz beneath in cool wet conditions).
Neem oil
Neem oil is a yellow-brown vegetable oil pressed from the seeds of Azadirachta indica (the neem tree). Diluted as a foliar spray, it acts as a contact suffocant, feeding deterrent, and partial systemic against aphids, whiteflies, thrips, mites, scale, and some fungal diseases. Generally low-toxicity to mammals but harmful to bees if sprayed directly.
Plant quarantine
Plant quarantine is the practice of isolating new, sick, or recently-imported plants from the rest of your collection for 2 to 4 weeks to make sure they are not carrying pests or disease. The single highest-leverage habit for protecting an indoor plant collection.
Saprophytic
A saprophytic organism feeds on dead or decaying organic matter rather than living plant tissue. Most beneficial soil fungi, mushrooms in compost piles, and the sooty mould growing on honeydew are all saprophytic — they look alarming but rarely cause disease in healthy plants.
Scale
Scale insects are small sap-sucking pests that attach to stems and leaves under a hard or waxy protective shell, looking more like bumps than insects. They drain plant vigor and excrete honeydew that supports sooty mold.
Sooty mold
Sooty mold is a dark, soot-like fungal growth that colonises the sugary honeydew excreted by sap-sucking insects. It does not invade plant tissue but blocks light, reduces photosynthesis, and signals a hidden pest problem.
Systemic insecticide
A systemic insecticide is absorbed by the plant and moves through its tissues, killing sap-sucking insects that feed on the treated plant. Neonicotinoids are the best-known class — but they are heavily restricted in the UK and EU because of harm to pollinators. Use is now banned outdoors in the UK as of 2025.
Thrips
Thrips are slender, fast-moving insects about 1 to 2 mm long that rasp plant tissue and suck the released sap. Damage shows as silvery streaks, stippling, and tiny black fecal specks on leaves and petals.
Vascular wilt (verticillium and fusarium)
Vascular wilt diseases are soil-borne fungal infections — most commonly Verticillium and Fusarium species — that invade a plant's xylem and block water transport. Symptoms include sudden one-sided wilting, yellowing leaves, brown streaks inside cut stems, and rapid collapse. There is no cure once infected.
Whitefly
Whiteflies are tiny moth-like insects, around 1 to 2 mm long, with powdery white wings. They cluster under leaves and fly up in a small cloud when disturbed, leaving behind honeydew and yellowed foliage.