The Complete Gardener's Guide,

All plants need moisture, nutrients, sunlight, and a suitable temperature for healthy growth and optimal development. However, they will need different levels of each depending on the natural habitats in which they have evolved.

Moisture


Water is vital for plants since it is used in photosynthesis and to keep leaves and stems firm and upright. Plants have a variety of methods to absorb and store it. Most take up moisture through microscopic root hairs and lose it via the leaves in a process called transpiration. This cycle enables sugars and nutrients to be circulated. Plants from arid regions, such as cacti, often have a reduced leaf area and a waxy coating to control moisture loss. Water-loving bog plants, such as gunnera and some irises, need moisture-rich sites at the margins of garden ponds and pools.

Temperature

Plants are classified according to hardiness: tender specimens tolerate temperatures down to 41ºF (5ºC), frost-hardy to 23ºF (-5ºC), and fully hardy to -4ºF (-20ºC). Every plant has specific temperature requirements; young plants are especially vulnerable and usually need protection to survive. Seedlings that have been raised indoors should be gradually introduced to cooler outdoor temperatures, a process known as “hardening off.” Frost-sensitive plants should be wrapped up in situ or moved to a frost-free location over winter. Tender, exotic plants, such as cacti, aloes, and agaves, require a warm, dry site and need protection against frost in cold winter climates.

Sunlight

Sunlight powers plant growth in the process of photosynthesis. The green parts of plants, which contain the pigment chlorophyll, absorb light and use it to convert carbon dioxide and water to sugar and starches. These compounds make cellulose, the building block of plant tissue. Shoots and leaves will move to trap light as efficiently as possible, but if they receive an insufficient amount or a restricted spectrum, they become pale and drawn, or “etiolated.” Plants that are adapted to heat and bright light tend to have small or narrow, even needle-like, leaves and may have various “sunscreens,” such as dark masking pigments or silver-gray felting. Shade-adapted plants often have broad leaves or large leaves made up of smaller leaflets, which allow them to absorb as much light as possible. In full sun shade plants may scorch since they are unaccustomed to the high light levels. The large surface area of the leaves of the banana plant enable it to absorb light.

Nutrition

Plants need three key elements and a range of trace elements for healthy growth. Nitrogen (N) governs the growth of leaves and shoots; potassium (K), or potash, is required for flowering and fruiting; and phosphorus (P) promotes strong root growth. Adverse growing conditions, such as underwatering or incorrect pH, can inhibit absorption. When plants run short of these, they show deficiency symptoms including stunted or distorted growth or discolored foliage. Specially balanced fertilizers are available for some plants. Fast-growing plants such as Rosa ‘The Fairy’ have greater nutritional demands than plants that are adapted to poor or dry soils.

The Complete Gardener's Guide - Book Cover
The Complete Gardener's Guide,

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