Before researching how to grow a specific plant, a gardener needs to understand what plants are, how they grow, and what they need. This lesson covers the basics.
Assumed audience
- Reading level: general adult.
- Background: has completed the introduction to gardening lesson.
- Goal: understand the fundamental needs of plants and the vocabulary used to describe them.
What a plant is
A plant is a living organism that makes its own food from light, water, and carbon dioxide through a process called photosynthesis. Most garden plants are vascular plants, meaning they have internal systems for transporting water and nutrients.
Parts of a plant
A garden plant has four main parts that a gardener needs to understand:
- Roots: the underground portion that anchors the plant in soil and absorbs water and dissolved minerals. Roots also store energy in some species.
- Stems: the above-ground structure that supports leaves, flowers, and fruit. Stems transport water up from roots and sugars down from leaves.
- Leaves: the primary site of photosynthesis. Leaves absorb light and carbon dioxide from the air, and release oxygen and water vapor.
- Flowers and fruit: the reproductive structures. Flowers produce seeds, often enclosed in fruit. Not all garden plants are grown for their fruit; some are grown for leaves, roots, or stems.
How plants grow
Plants grow by converting light energy into chemical energy through photosynthesis. In simplified terms:
- Roots absorb water and dissolved minerals from the soil.
- Leaves absorb light and carbon dioxide from the air.
- The plant uses these inputs to produce sugars, which fuel growth.
- The plant releases oxygen and water vapor as byproducts.
Growth requires all of these inputs in adequate amounts. If any one is insufficient, growth slows or stops.
What plants need
Every plant requires five things from its environment:
- Light: the energy source for photosynthesis. Different plants need different amounts. “Full sun” means at least six hours of direct sunlight per day. “Partial shade” means three to six hours. “Full shade” means fewer than three hours.
- Water: absorbed by roots, used in photosynthesis and to maintain cell structure. Too little water causes wilting; too much drowns roots by displacing the air they also need.
- Nutrients: minerals dissolved in soil water, primarily nitrogen, phosphorus, and potassium. Plants also need smaller amounts of calcium, magnesium, sulfur, and trace elements. Nutrients come from the soil, from decomposing organic matter, or from fertilizer.
- Temperature: plants have a range of temperatures in which they can grow. Outside that range, growth stops. At extremes, the plant dies. Frost (temperatures at or below 0°C / 32°F) damages or kills many garden plants by freezing the water inside their cells.
- Space: roots need room to spread in soil, and above-ground parts need room for air circulation and light access. Crowded plants compete for all of the above resources.
Plant life cycles
Plants are classified by how long they live:
- Annual: completes its entire life cycle — germination, growth, flowering, seed production, and death — in a single growing season. Examples: tomatoes, basil, lettuce.
- Biennial: takes two growing seasons to complete its life cycle. It grows leaves and roots in the first year, then flowers and produces seed in the second year before dying. Examples: carrots, parsley, onions.
- Perennial: lives for more than two years, often many. It may die back to the ground in winter and regrow from its roots in spring. Examples: rhubarb, asparagus, most fruit trees.
A gardener needs to know a plant’s life cycle because it determines when to plant, what to expect each season, and whether the plant will return the following year.
Growth habits
Plants grow in different shapes, which affects how much space they need and what support they may require:
- Upright: grows vertically with a single main stem or a few branches. Examples: peppers, sunflowers.
- Bushy: grows into a rounded mass of stems and leaves. Examples: basil, most beans.
- Vining: produces long flexible stems that climb or sprawl. Requires a trellis, cage, or open ground to spread across. Examples: cucumbers, peas, squash.
- Rosette: grows as a low cluster of leaves radiating from a central point. Examples: lettuce, spinach.
Species and cultivars
A species is a group of plants that share the same basic characteristics and can reproduce with each other. A cultivar (short for “cultivated variety”) is a specific version of a species that has been selected or bred for particular traits — such as fruit size, color, disease resistance, or climate tolerance.
When researching how to grow a plant, the cultivar matters as much as the species. Two cultivars of the same species may have different temperature tolerances, days to maturity, or disease resistance. Seed catalogs and plant labels identify plants by both species and cultivar.
Why these basics matter
Every later lesson in this discipline builds on these concepts. When a lesson refers to “light requirements,” it means the amount of direct sunlight the plant needs for photosynthesis. When it mentions “soil pH,” it relates to how available nutrients are to the plant’s roots. Understanding the basics makes every subsequent decision more informed.