No matter how good your soil, it will probably need extra nutrients to help plants with specific needs, or to boost them at key times, like flowering. Always follow the instructions on the label because too much, or the wrong type of fertilizer, can cause problems, such as plants with all leaves and no flowers.
The three basic elements that plants require are nitrogen (N), phosphorus (P) and potassium (K). Nitrogen is needed for leaf and shoot growth, phosphorus for roots, and potassium helps flowers and fruits develop. Fertilizer manufacturers list the nutrient content as a ratio: a general purpose fertilizer has an N:P:K ratio of 7:7:7, while a tomato feed has a high concentration of potassium to boost fruit production, and a fertilizer for lawns or leafy crops contains mostly nitrogen.
Many fertilizers also include various trace elements or micronutrients. A plant’s nutrient requirements can depend on its growth phase, with most needing a general boost in the spring, and additional potassium as they fruit or flower.
Your local garden center will offer both organic (derived from plants and animals) and inorganic (chemically manufactured) fertilizers. Most are concentrated for convenience and available as liquids, powders that you dilute in water, or granules. Typical examples of organic fertilizers are pelleted chicken manure; blood, fish, and bonemeal; liquid seaweed fertilizer; and homemade plant feeds, such as the diluted liquor from a wormery, or fertilizers made from soaking comfrey leaves. Inorganic feeds include sulfate of potash, Growmore, and granular rose feeds.
Materials spread on top of the ground, usually around plants, are called mulches. They can be practical—feeding the soil, suppressing weeds, retaining moisture, or insulating roots in winter—or mainly decorative, applied for visual effect.
Applying organic mulches
Mulches are applied at different times depending on their purpose. For example, bark chips are spread over the soil after planting to suppress weeds. An organic mulch, such as manure, garden compost, chipped bark, or cocoa shells, must be laid over moist soil, whether in spring, after autumn and winter rains, or after watering.
Some mulches, especially bark, use up nutrients temporarily as they decompose, so before laying them, apply a nitrogenrich fertilizer, such as fish meal. Lay organic mulches in a layer 4in (10cm) deep so they continue to provide cover as they slowly decompose and feed the soil. Replenish these mulches every year.
Man-made mulches offer many benefits. Weed membrane or landscape fabric is a semipermeable material that blocks out light but allows moisture through. Use it on low-maintenance beds, or on weed-ridden ground. Lay it before planting and cover with a natural bark or gravel, or a decorative mulch.
Black plastic does not allow moisture through, but it warms the soil and kills off weeds when laid over vegetable beds in spring. Straw insulates the soil, and protects tender plants in winter. It is also used to raise crops, such as strawberries and zucchinis, off the ground, reducing fungal and slug problems. A think layer of straw will protect the roots of vulnerable plants from frost.
Mulches that don’t decompose are useful as decorative garden surfaces. They are particularly effective when laid over landscape fabric or membrane, which reduces weed growth and helps prevent soil mixing in with the mulch and spoiling the effect. For a modern feel, try colored crushed glass or slate shards. Cover small areas, like the tops of pots and containers, with beads, crushed and whole shells, or polished pebbles. Natural pebbles blend well with gravel over larger areas, and can create a beach effect when laid in swathes.