It is often assumed that poor growth in garden plants is related to lack of fertiliser.
This is not always the case as some other factor/s may be causing the non-uptake of nutrients from the soil.
Things such as an imbalance in nutrients, wrong soil ph, soil too dry/too wet or disease to name but a few.
A soil test is the best way to establish such problems.
As a rule of thumb:
Plants in containers will need regular feeding.
Plants in the borders will generally survive for the season on a top dressing of a general or balanced fertiliser at planting out time.
Perennials usually require feeding when new growth commences.
Fruit bearing and flowering plants will often benefit from a high potash feed when the embryo fruit or flower buds appear.
*See the list below for feeding times of specific plants.
The nutrients a plant requires for growth are, nitrogen, phosphorus and potash (NPK), supported by a range of trace nutrients.
The first three nutrients are required in large amounts but the ratio can vary a lot from crop to crop.
For example; brassicas such as cabbage require higher amounts of nitrogen than root crops such as onions or carrots, where as shrubs and trees need more phosphorus and potash.
The same is also true of the trace elements, as the term implies, only a trace is required, for healthy growth even if there is enough NPK available.
Nitrogen (N) is necessary for development of leaves and stems.
Phosphorus (P) is for strong root systems.
Potash (K) is for healthy fruit, tubers, and leaves.
Where possible, choose a formula that matches your plant's requirements.
Soil conditions can influence the availability of nutrients, e.g. soil compaction and water-logging can stop essential nutrients being usable.
Light, sandy soils are often high in phosphates and low in potash.
Clay contains lots of potash that becomes available as the soil is aerated and limed.
Accurate assessment can be made by soil analysis, to determine deficiencies.
Bulky, animal manures, mushroom compost and garden compost are best applied during the dormant season.
They can either be applied as surface mulch, or dug into the soil.
Adding lime to the soil is an important resource, but is determined by the amount already in the soil and the type of plants being cultivated.
Check your soil pH and add lime as necessary.
Sandy soils usually lack lime.
Avoid over-liming as this could lock up some trace elements.
Do not add lime to recently manured soil!
Asparagus: Before growth stars in Spring
Aubergine: After fruit sets.
Broad beans: After pod set.
Broccoli: Three weeks after planting out, then as required.
Brussels Sprouts: Two to four weeks after planting out or when plants are 300mm high.
Cabbage: Three weeks after planting out.
Calabrese: Three weeks after planting out, then as required.
Cauliflower: Three weeks after planting out.
Cucumber: One week after plant blossoms and again three weeks later.
Globe Artichoke: Planting time and monthly top dressings.
Gourds/Squashes: A month after emergence from soil.
French beans: After pod set.
Kale: When plants are approx 300mm (12") tall.
Lettuce: Two/Three weeks after transplanting or emergence from soil.
Melons: At planting out time.
Onions: When bulbs begin to swell.
Peas: Once established and when pods set.
Peppers: After fruit sets.
Potatoes: When in flower.
Rhubarb: Before planting out.
Runner beans: After pod set.
Spinach: When plants are approx 300mm (12") tall.
Sweet corn: When 200mm (8") and again when silks appear.
Tomatoes: After fruit set then weekly.
Water melon: When plants are approx 300mm (12") tall.