The Gardening Terms Glossary: What ‘Bolting,’ ‘Deadheading,’ and ‘Direct Sow’ Actually Mean

Read three plant-care guides in a row and you’ll hit “harden off,” “bolting,” and “amend the soil” without a single one stopping to explain what those words actually mean, or what happens if you skip the step they describe. Gardening media assumes a vocabulary most beginners haven’t built yet. Most glossaries that do exist just hand you the bare definition — “bolting: when a plant goes to seed” — without the reason it matters or what you’d do differently because of it.

This glossary covers 40 terms every new gardener runs into, grouped the way you’ll actually encounter them: what kind of plant you’re growing, what you’re growing it in, how you get it started, how you keep it alive, how far apart to space it, and when the calendar makes the decision for you. The terms that carry real physiological weight — bolting, hardening off, damping off, deadheading — get the mechanism behind them, sourced from university extension research, not just a one-line definition. An alphabetized table near the end covers all 40 for quick scanning once you already know them.

Plant Life & Reproduction Terms

These are the words seed packets and plant tags throw at you before you’ve even decided what to grow. Get them straight first — everything else in this glossary builds on them.

Annual: A plant that completes its entire life cycle — germination, flowering, seed production, death — in a single growing season. Petunias and most vegetables are annuals; when frost hits, they’re done for good.

Three pre-planned garden beds, free

Stop staring at empty beds: printable plans with exact layouts, plant lists and planting calendars — yours free from the Garden Library.

Send me the plans

I agree to receive emails from Blooming Expert and accept the Privacy Policy. Unsubscribe anytime.

Biennial: A plant that needs two growing seasons to complete its cycle. Year one it builds leaves and roots; year two it flowers, sets seed, and dies. Carrots, parsley, and foxglove all work this way — which is why a carrot left in the ground over winter suddenly bolts to flower the following summer instead of staying a root worth eating.

Perennial: A plant that lives three or more years, dying back to the roots (or staying evergreen) each winter and regrowing the following spring. “Perennial” describes lifespan, not appearance — some perennials look nothing alike season to season.

Cultivar: Short for “cultivated variety” — a plant selected and bred by humans for a specific trait (flower color, disease resistance, compact size) and reproduced to keep that trait consistent. “Tomato ‘Cherokee Purple’” — the part in quotes is the cultivar name.

Variety: In casual use, “variety” and “cultivar” get used interchangeably, but technically a variety occurs naturally within a species with no human breeding involved, while a cultivar is human-selected and maintained. Most of what’s sold in nurseries and seed catalogs is technically cultivars, even when the tag says “variety.”

Hybrid (F1): The first-generation offspring of two different parent plants, deliberately cross-bred for specific traits like higher yield or disease resistance. Seeds saved from a hybrid won’t grow true to the parent — the F1 vigor doesn’t carry to the next generation.

Heirloom: An open-pollinated cultivar that’s been passed down, seed to seed, for at least 50 years without commercial hybridization. Heirloom doesn’t mean “wild” or “untouched” — it means old and stable.

Open-Pollinated: A plant pollinated naturally — by wind, insects, or self-pollination — rather than through controlled hybridization. Seeds saved from an open-pollinated plant grow true to the parent, which is why heirlooms are always open-pollinated but not every open-pollinated plant is old enough to count as an heirloom.

Self-Sowing: A plant that drops its own seed and comes back the following year without replanting — often in a slightly different spot than where you planted it originally. Poppies, dill, and calendula are reliable self-sowers.

Soil & Amendment Terms

Once you know what you’re growing, the next vocabulary cluster is what you’re growing it in — and this is where a lot of beginner advice gets vague. “Improve your soil” means nothing without these words.

pH: A 0–14 scale measuring how acidic or alkaline your soil is, with 7.0 as neutral. Most vegetables and lawns want 6.0–7.0 — outside that window, nutrients like iron and phosphorus chemically lock into forms roots can’t absorb, so a plant can be starving in soil that’s technically full of nutrients. A $15 soil test is the only way to know your actual number instead of guessing from symptoms.

Amendment: Anything worked into the soil to change its structure or chemistry — lime to raise pH, sulfur to lower it, compost to improve drainage and water retention. An amendment isn’t the same as a fertilizer: fertilizer feeds the plant directly, an amendment changes the soil the plant grows in. A soil test tells you which amendment you actually need before you buy one.

Compost: Fully decomposed organic matter — food scraps, yard waste, manure — broken down by microbes into a dark, crumbly material that feeds soil life and improves structure. Finished compost doesn’t smell; if it does, it’s not done yet.

Humus: The stable, dark organic material left after compost and other organic matter have broken down as far as they’ll go. Compost eventually becomes humus; humus is what actually holds nutrients and moisture in soil long-term.

Mulch: A layer of material — wood chips, straw, shredded leaves — spread over bare soil to hold moisture, block weed germination, and moderate soil temperature swings. Mulch sits on top of the soil; amendments get worked into it.

NPK: The three numbers on every fertilizer bag (like 10-10-10), standing for nitrogen-phosphorus-potassium — the three nutrients plants need in the largest amounts. Nitrogen drives leafy growth, phosphorus drives roots and flowers, potassium drives overall hardiness and disease resistance.

Well-Drained Soil: Soil that lets excess water pass through within a few hours rather than pooling, so roots get oxygen instead of sitting in standing water. It’s one of the most common phrases in plant-care instructions and one of the least explained — if your soil holds water in a fist-sized hole for more than 4–6 hours after rain, it’s not well-drained, and most plant labels assume it is.

Starting & Planting Terms

This cluster covers the actual act of getting a seed or seedling into the ground — and it’s where beginners lose the most plants, usually from skipping a step whose purpose was never explained.

Direct Sow: Planting seed straight into its final growing spot, rather than starting it indoors and moving it later. Some crops require this: cucurbits like squash, cucumbers, and melons can only grow new roots from their original root system, not from stem tissue, so a torn root ball during transplanting simply won’t recover.^[1] Carrots, beans, and corn behave the same way.

Transplant: Moving a plant from one growing location to another — most often from a seed tray indoors to the garden bed. Crops like tomatoes and peppers tolerate this well because they can grow new roots along a buried stem; cucurbits and root vegetables generally can’t.

Germination: The process of a seed sprouting — absorbing water, activating enzymes, and pushing out a root and shoot. Germination rate, often printed on the seed packet, tells you what percentage of seeds are expected to sprout under ideal conditions, which is why sowing thicker than your final spacing is standard practice.

Hardening Off: Gradually exposing indoor-grown seedlings to outdoor sun, wind, and temperature swings over 1–2 weeks before transplanting, instead of moving them outside all at once. Indoor growth is soft and succulent; hardening off shifts that growth to firmer, tougher tissue that can handle wind and direct sun without collapsing.^[2] Skip it, and seedlings that looked perfectly healthy indoors can scorch or snap within a day outside.

Damping Off: A seedling disease caused by soilborne fungi — Pythium and Rhizoctonia are the usual culprits — that rots seedlings at the soil line, often overnight, in cool wet conditions or warm dry ones depending on which fungus is involved.^[3] It’s why “don’t overwater seedlings” shows up in nearly every starting guide: excess moisture is the single biggest risk factor.

Thinning: Removing extra seedlings after germination so the strongest ones have enough room, light, and nutrients to develop properly. The first time I thinned a tray of overcrowded lettuce seedlings, pulling perfectly healthy plants felt wasteful — but overcrowded seedlings compete for the same root space, and all of them end up smaller than if I’d thinned early.

Days to Maturity (DTM): The number of days from either germination or transplant date, check the packet, it varies, to first expected harvest. DTM is a guideline calibrated to average conditions, not a guarantee — a cool, cloudy season can push actual harvest a week or two past the printed number.

Growth & Care Terms

Once plants are established, the vocabulary shifts to keeping them productive — and this is where a couple of popular explanations turn out to be backwards.

Bolting: When a plant abruptly shifts from producing leaves to producing a flower stalk and seed, usually ending its usefulness as a food crop. The common explanation — “it’s the heat” — is backwards for most spring crops. Michigan State University Extension points to cold as the real trigger: many vegetables need a set number of cool hours after reaching a certain size before they’ll flower, a response called vernalization, and long daylight hours in late spring finish the job.^[4] Heat and drought stress can push a plant to bolt too, but blaming a single hot week ignores the weeks of cool weather that primed it.

Deadheading: Removing spent or faded flowers before they set seed. Most annuals put their energy into seed production once flowers fade, which slows new blooming; removing the spent flower redirects that energy back into producing more flowers instead.^[5]

Pinching: Removing the growing tip of a stem, often just with your fingers, to force the plant to branch out sideways instead of growing one tall stem. Basil and mums get pinched regularly to stay bushy instead of leggy.

Staking: Providing physical support — a stake, cage, or trellis — for plants whose stems can’t support their own fruit or flower weight. Indeterminate tomatoes and dahlias get staked; determinate bush varieties usually don’t need it.

Succession Planting: Sowing the same crop in small batches every 1–3 weeks instead of all at once, so harvest is staggered over a longer window instead of arriving in one glut. Lettuce and radishes are the classic succession crops because they mature fast and bolt quickly once they do.

Companion Planting: Growing certain plants near each other for a practical benefit — pest confusion, shade, structural support, or attracting pollinators — rather than by pure aesthetic layout. Basil interplanted with tomatoes for pest deterrence is the best-known example, though the evidence behind specific pairings ranges from well-documented to mostly anecdotal.

Crop Rotation: Changing which plant family grows in a given bed each year, rather than replanting the same family in the same spot. Rotation breaks the life cycle of soil-dwelling pests and diseases that target one plant family and keeps the same nutrients from being depleted in the same spot year after year.

Spacing & Layout Terms

Where you put plants relative to each other and the sun determines whether every other term in this glossary actually pays off.

Spacing: The recommended distance between plants, and between rows, printed on seed packets and plant tags to give each plant enough root room, airflow, and light at mature size, not seedling size. Crowd plants closer than their spacing calls for and you get more competition for water and nutrients, worse airflow, which raises disease risk, and often a lower total yield than if you’d spaced correctly. A spacing chart with exact distances for 40+ crops takes the guesswork out of this.

Full Sun / Part Shade / Full Shade: Full sun means 6+ hours of direct sunlight daily; part shade means 3–6 hours, often filtered or morning-only; full shade means under 3 hours. These aren’t interchangeable — a “full sun” tomato getting part-shade light will grow leggy and produce a fraction of its potential fruit, not just “grow a little slower.”

Row Cover: A lightweight fabric laid directly over crops to block insects, add a few degrees of frost protection, or both, depending on the fabric weight. Lighter weights let more light through but offer less cold protection — you trade one for the other.

Intensive Planting: Spacing plants closer than traditional row spacing, often in a grid instead of rows, to maximize yield per square foot, usually paired with heavier soil amendment to support the denser root competition. It works, but it raises the stakes on getting your soil fertility right first, since there’s less soil volume per plant to draw from.

Zone & Timing Terms

The last cluster is about calendar and climate — the vocabulary that tells you not just what to plant, but when.

USDA Hardiness Zone: A number, 1 through 13, with a/b half-zones, assigned by the USDA based on a region’s average annual extreme minimum winter temperature, used to predict which perennial plants will survive the winter there.^[6] It says nothing about summer heat, rainfall, or humidity — two gardens in the same zone can need completely different care. UK readers will see RHS hardiness ratings instead, which use a different H1–H7 scale, not USDA zone numbers.

Frost Date: The average date of the last spring frost or first fall frost for your area, used to time planting so tender crops aren’t killed by cold. “Average” is doing a lot of work in that definition — actual frost can land a week or two on either side of the average date in a given year, which is why experienced gardeners treat it as a planning guide, not a guarantee.

Chill Hours: The cumulative number of hours a fruit tree or shrub spends roughly between 32–45°F over winter, required before it will break dormancy and flower normally in spring. Plant a low-chill variety in a cold climate, or a high-chill variety in a mild one, and you’ll get poor or no flowering even with otherwise perfect care.

Cold Frame: A low, bottomless box with a clear lid, set directly over soil or plants, that traps solar heat to extend the growing season on both ends — hardening off seedlings in spring, protecting greens into early winter.

Determinate / Indeterminate: Determinate plants, like bush tomatoes and most modern potato varieties, grow to a fixed size, set all their fruit within a short window, and stop — useful for one big harvest for canning. Indeterminate plants keep growing and producing until frost or disease stops them, which is why indeterminate tomatoes need staking and determinate ones usually don’t.

Dormancy: A plant’s resting state, triggered by shortening days and dropping temperatures, where growth stops and the plant conserves energy until conditions improve. Deciduous trees and many perennials rely on a real winter dormancy period to flower and fruit properly the following year, part of why chill hours matter so much for fruit trees.

Quick-Reference: All 40 Terms, A to Z

Once you’ve read the explanations above, use this table to look a term back up without hunting through the sections.

Frequently Asked Questions

What’s the difference between a cultivar and a variety?
Technically, a variety occurs naturally within a species with no human breeding involved, while a cultivar is deliberately selected and maintained by growers. In everyday nursery and catalog use the two words get swapped constantly, and most of what you’ll actually buy is a cultivar even when the tag says “variety.”

Do I need to memorize all 40 of these terms before I start gardening?
No. Bookmark this page as a reference instead. The terms worth learning first are whatever you’re running into in the guide you’re currently reading — the rest will stick once you’ve hit the situation they describe.

Why does gardening have so much specialized vocabulary in the first place?
Most of these terms compress a specific plant-physiology mechanism into one or two words. “Bolting” is faster to say than “the cold-triggered shift from vegetative to reproductive growth.” Once you know the mechanism behind the word, the word stops being jargon and starts being useful shorthand.

The Vocabulary Is Shorthand, Not Gatekeeping

None of these 40 terms are complicated once you know the mechanism behind them: bolting is a cold-triggered hormone shift, hardening off is tissue toughening, deadheading is energy redirection. The vocabulary just compresses that mechanism into a word so growers don’t have to re-explain the biology every time. I still keep a version of this list taped inside my potting shed instead of trying to hold it all in my head. Keep this page bookmarked as a reference rather than trying to memorize it — the terms that matter will come up naturally as you work through your first season. If you haven’t mapped out that first season yet, our guide to starting a garden from scratch is the logical next stop.

Sources

1. University of Delaware Cooperative Extension — Transplants: Understanding the Differences in Rooting and Plant Survival in Cold Soils
2. University of Maryland Extension — Hardening Off Vegetable Seedlings for the Home Garden
3. NC State Extension — Damping-Off in Flower and Vegetable Seedlings
4. Michigan State University Extension — Bolting in Spring Vegetables
5. Clemson Cooperative Extension, Home & Garden Information Center — The Gardener’s Toolkit: Deadheading
6. USDA Agricultural Research Service — USDA Plant Hardiness Zone Map