composts. They are formed mainly of mixtures based on granulated peat and are uniform, as well as lighter and cleaner to use than loam-based types. Both have advantages and disadvantages.
Understanding the Term “Compost”
The term compost is often confusing and can be interpreted in several ways. Here are a few terms you might encounter.
Potting composts are free from pests and diseases and are specially formulated to encourage the active growth of roots, providing suitable plant foods, air, and moisture. All references in this book to “compost” are solely to potting composts.
Loam-based composts are primarily based on partially sterilized loam.
Soil-less composts, often known as soil-less compost mixes, are mainly formed of granulated peat and, for that reason, are frequently called peat-based composts.
Garden compost is derived from organic waste material from gardens and kitchens that has been placed in a compost heap or bin and allowed to decay. Eventually, this material, when fully decayed and friable, is either dug into soil to improved its structure and fertility, or spread on the surface of bare soil or around (but not touching) established plants to increase soil fertility and inhibit the growth of weeds (known as mulching). The decaying process can take up to a year and is influenced by temperature, bacteria activity, air, and moisture. This material is not a suitable compost in which to grow house plants.
Garden soil (sometimes just referred to as potting soil) is not suitable for house plants as it has a variable nature and may contain an imbalance of clay, silt, and loam as well as being contaminated by pests and diseases. It may also be excessively acidic or alkaline and nutritionally imbalanced.
Loam-Based Composts
are heavier than peat-based types, giving greater stability to plants, especially those with a mass of foliage
are unlikely to dry out as fast or as completely as peat-based types
have a larger reserve of minor and trace plant foods than peat-based types
are suitable for most houseplants
Peat-Based Composts
are more uniform than loam-based composts
are easily carried home in bags and stored (seal the bag’s top by folding it over)
are light and easy to use
dry out more quickly than loam-based types and are more difficult to remoisten if watering is neglected
require plants to be fed at an earlier stage in their growth than with loam-based composts
Other Types of Compost
The continued removal of peat from peat beds has destroyed the environments of many animals, birds, insects and native plants, so there has been pressure to use more environmentally friendly composts. These are formed of several different materials, some of which are also used as additives to other composts to help retain moisture. Look for peat-free composts when buying soil-less types.
Specialist Composts
The range of plants grown indoors is wide, and it is clear that just one type of compost will not suit them all. Most flowering and foliage houseplants grow well in loam-based or peat-based composts (but do not change the type of compost when repotting a plant). Specialist plants, such as cacti and bromeliads, need types better suited to their specific needs. These can be purchased from garden centers and specialist outlets.
For healthy plants, sunlight and the correct ambient temperature for the species are vital.
Light and Warmth
Sunlight is essential for plants to grow, and it must be in balance with temperature. In the wild, these are usually in harmony: as light intensity rises, so does the temperature. However, in homes—especially in winter—the temperature may be high but the light intensity low. Adjustments can be made to the temperature, but the temperature is usually selected to suit people rather than plants.
The intensity of light varies from one season to another, as well as throughout the day. In the plant directory in Part Two, the amount of light needed in winter and summer is indicated for each plant.
Light intensity rapidly decreases as distance from a window increases. The amount of illumination at 8ft (2.4m) from a window is 5–10% of that of the light reaching a windowsill.
Temperatures vary throughout the year; those to suit plants in winter and summer are indicated in the individual listings in Part Two.
In general, flowering houseplants need more light than those grown mainly for their foliage, while cacti require good light at all times.
Plants should not be moved suddenly from dull light to strong light.
Keep windows clean, especially during winter when light intensity is low. In summer, sheer curtains help to diffuse strong sunlight.
Rooms decorated in light colors reflect more light than dark shades—a major benefit in winter.
Leaves and stems soon turn toward the light source, causing distortion. Counteract this by turning plants a quarter of a turn every few days.
In winter, plants close to windows may receive good light but be exposed to drafts from ill-fitting window frames, causing flower buds to fall off.
The Need for Water
Like all living things, plants are mainly formed of water and, if deprived of it, eventually die. Some, such as cacti and other succulents, have water-storage mechanisms in their leaves and stems, but most plants need a regular supply. The amount required varies through the year and is influenced by light intensity and temperature.
Water the compost and allow to drain.
Watering a Houseplant
There are several ways to water a houseplant. The usual method is “over the rim.” This involves using an indoor watering can to pour water into the space between the top of the compost and the rim of the pot. Allow water to seep into the compost and drain through it into a saucer. After about 10 minutes, tip away excess water from the saucer.
Alternatively, where it is essential not to moisten the leaves (especially those that are hairy and soft, such as saintpaulias and Episcia cupreata), stand the pot in a bowl shallowly filled with water. When moisture rises to the compost’s surface, remove the potted plant and allow excess water to drain.
How to Judge If a Plant Needs Water
More houseplants die each year from too little or too much water than for any other reason. Judging when to water is a skill derived from experience, although in recent years several specialized pieces of equipment have helped to take the guesswork out of this task. Year-round
