Plant Fertilizer
Plant Fertilizer of some sort are needed by every gardener to get the best from their plants; we explain what plant fertilizer does, when it is applied and how to spot symptoms of low nutrient levels.
To get the best growth from your plants they will almost always need plant fertilizer at some stage. In any garden or
container, especially if the plants are packed tight together, a complete plant fertilizer or specific nutrients should be used. The secret of gardening success lies in keeping the soil in good condition by applying plenty of organic matter in the form of well-rotted farmyard manure, homemade garden compost or
leafmould; this feeds the vital creatures and microbes that live in the soil, which in turn break down the organic matter into nutrients that the roots and leaves can absorb. Healthy plants are better able to withstand pest and disease attack than sick ones.
The following chart shows which nutrients in plant fertilizer are needed.
Nutrients
| Nutrient |
Which Plants |
Which Soils |
Signs of Shortage |
| Nitrogen |
All.
Needed for flower production |
Most Soils
Poor Soils |
Pale leaves
Looks unhealthy |
| Phosphate |
All; needed for root development |
Most soils Sandy or poor soils |
Poor root development Stunted growth |
| Potash |
All.
Needed for flower and fruit growth |
All soils
Needed to balance high nitrogen fertiliser or manure |
Poor flowering; few fruits or berries.
Prone to frost damage |
| Magnesium |
All.
A major constituent of chlorophyll |
Sandy, acid, wet soils
Needed to balance high potassium content |
Yellow or brown patches around leaf edges and between leaf veins |
| Iron |
All.
Plants intolerant of alkaline soil e.g. Rhododendrons, Azaleas |
All soils
Balances high pH caused by chalk, limestone or lime |
Yellowing between leaf veins especially new growth |
| Other Nutrients |
Minor nutrients and trace elements required in small amounts |
Light soils
Heavile cropped areas |
General poor growth |
When and How to Apply Plant Fertilizer
There is a correct time to apply plant fertilizer. Feeding late in the season encourages new soft growth which is then susceptible to early frosts; late feeding can also lead to buds failing to open on ornamental shrubs such as camellias. Any concentrated plant fertilizer should be kept away from leaves, stems or flowers as it will cause leaf scorching. The exception is foliar feed applied at the correct concentration as per the manufacturers instructions.
There are hundreds of plant fertilizers available commercially with a wide variety of composition and form, from liquids, slow release pellets, sticks to push into soil, tablets, granules and powders. Choose a plant fertilizer that has been developed for the specific needs of your plants and apply at the correct time of year. Always keep a separate watering can or container to apply liquid and foliar feeds and never use the same vessel to apply chemical pesticides in your garden; label clearly to avoid costly errors!
Types of Plant Fertilizer
Manure
This is a particularly rich source of nitrogen and trace elements but it needs to be well rotted before applying. The most common source is farmyard manure, often sold in bags, but also available by the trailer load from local farms. Make sure you know where it came from - recent reports (June 2008) in the UK concerned contaminated manure originating from farms where the hormone-based herbicide aminopyralid had been sprayed on fields. The aminopyralid was present in only small amounts, however, even trace levels are enough to affect plants which are particularly sensitive to this substance. These include potatoes and tomatoes, peas and beans, carrots and lettuce, and related crops which fail to grow properly or, in some cases, may even fail to grow at all.
Apply as a mulch in the cut flower garden.
Mushroom Compost
Use to improve soil texture. It also contains a range of nutrients
Seaweed extract
Available as a liquid which can be used on the soil or as a foliar feed. It contains nitrogen, potash and phosphate.
Bonemeal is a good source of phosphate. Fish, blood and bonemeal is a good general plant fertilizer providing phosphorous, nitrogen and potassium.
Sulphates of Ammonium or Potash
Suphate of ammonium contains concentrated nitrogen; suphate of potash provides potassium.
Woodash
This contains a small amount of potassium.
Safety and Storage of Plant Fertilizers
Always wear goves when applying plant fertilizer and do not breathe in vapour or dust. Read instructions on commercially available plant fertilizers and use only the recommended quantities - you will not get better results by adding twice as much half as often!
Store plant fertilizers in a cool, dry, dark place such as in your
garden shed and check containers are tightly closed and out of the reach of children and animals.
