Heeling-in: What you are doing when you temporarily plant a tree or shrub in a holding-bed until you are ready to find a permanent home for it. Humus: Dark brown organic material formed from the decomposition of vegetable and certain animal matter. Humus is necessary to enrich soil and give it the necessary life to nourish and sustain plants. Hybrid: A new plant produced by crossing two genetically different plants from the same or a closely related species. Not all hybrids are improvements on the parent species.

I Insecticide: Chemical or soap-based spray used to control or kill such insect pests as aphids and red spider mites. Island bed: Novel way of growing perennials. Instead of the traditional, long, yew-backed border, perennials are displayed in a circle, with the tallest (often delphiniums) in the centre.

J Jardin de refuse: Polite way of describing temporary lodgings for plants you can't use, but can't bring yourself to throw away. Juvenile foliage: New leaves that look different in their shape, size and colour to the plant's more familiar adult foliage.

K Knot-garden: An invention of medieval English gardeners who liked to weave low-growing herbs or boxwood hedging into elaborate, knot-like geometric patterns, sometimes with herbs or roses interplanted. L Layering: A way of propagating in which a trailing branch of a plant is bent down and anchored below ground level

until roots form and the newly established plant can be safely cut away from the parent. Leaf mould: Rotting or partly decomposed leaves that can be used as a mulch or dug into the soil to create useful organic matter. Loam: The best kind of soil; moderately fertile, composed of clay, sand and humus with a texture that is neither too sandy nor too heavy.

M Mulch: A layer of bulky organic matter usually placed around perennials to reduce moisture loss, inhibit weeds, improve soil and protect plants from frost. Good mulches include grass clippings, well-rotted compost and leaf mould. Manure tea: Water in which compost has been allowed to soak to form a mild, fertilizing `tea.'

N Native plant: Species that grows naturally in a certain location and not created by human cultivation. Naturalize: Informal planting that mirrors nature's own relaxed style and design to create the impression that the plants are native. NPK: Key plant-food ingredients of fertilizer: N for nitrogen, P for phosphorous and K for potassium. The numbers

represent the percentage of each element in the mix. One way to remember what each chemical does is to memorize, Little Red Flower (L for leaf, fed by nitrogen; R for roots, strengthened by phosphorous, F for fruit or flower, promoted by potassium.) O Oxygenator: A submerged water plant that helps keep ponds clean by releasing oxygen into the water.

P Perennial: A plant with the ability to survive winter and live on for several growing seasons. pH: Measure (1 to 14) of acidity or alkalinity of soil. Lilac won't thrive in acidic soil, rhododendrons hate alkaline soil. The lower the pH the higher the acidity. Pollarding: Cutting back the main branches of a tree to within inches of the trunk to create a distinct globe-effect.

Pricking out: Careful removal of seedlings from the original seed-tray into a roomier pot or growing space. Pinching back: A way of encouraging bushiness in a plant by using your finger and thumb to pinch off growing tips. Q Quercus: The botanical genus name for the oak family. Few English people know that their famous mighty oak is actually called Quercus robur. CONTINUE