Fertilisers

Trees and shrubs will survive satisfactorily with little or no feeding. However, if they are fed, especially in the first year or two, they will thrive. Fruits, vegetables and flowers definitely respond to feeding, resulting in much more pleasure and satisfaction from your efforts.

Nutrients required for growth

To be healthy and thriving plants require a balance of nutrients. (Although members of the protea family and some NZ natives require only small amounts). Some soils, in particular sandy soils, require more fertiliser than clay soils

The major elements required for plant growth are Nitrogen (N), Phosphorus (P) and Potassium (K). These are required in large amounts. Fertilisers which contain these three are sometimes referred to as NPK fertilisers (or complete fertilisers) and the percentage of each is referred to as the NPK content. A good NPK or complete fertiliser for plants in pots is likely to contain a ratio of 10%N 4%P and 8%K, while one for application to soils may contain a ratio of 6%N, 5%P, 5%K.

In addition to the major elements, minor and trace elements are required. These trace elements are required by plants in very small amounts. In most soils these are available naturally in adequate amounts. However, they could be deficient in pot or container plants after a year or so.

Occasionally minor or trace element deficiencies show up in plants. Where this is suspected, bring a sample in to our garden adviser.

Soil Acidity

The acidity of soil has an effect on availability of elements required for growth. Plants grow best in soils that are slightly acid. Fortunately most soils naturally fall in this band. Organic soils high in compost may be more acid and some chalk soils or clays may be too alkaline. If most of your plants fail to thrive and acidity is suspected seek advice from our garden adviser.

There are a few plants such as azaleas, camellias, rhododendron, daphne and boronia, along with lawns, which prefer an acid soil.

Very acid soils are improved by adding Lime. Alkaline soils are improved by adding compost, sulphate of iron or sulphur.

Which Fertiliser to Use

Which fertiliser to use depends mostly on where the plant is growing, (in the soil or in a pot) and whether the application is at planting time or a top dressing later to established plants.

At Planting Time - Trees, Shrubs, Roses, etc. 

• Ican Slow Food 24 Month Fertiliser - up to two years of balanced feeding.
• Tree and Shrub Planting Tablets – up to 24 months of Feeding
• Tui Sheep Pellets – a fertiliser and soil conditioner 

When applied at planting time, these fertilisers release the nutrients over a 3 – 24 month period, which gives plants a very good start. Because they release slowly, they are safe to use around the roots at planting time.

Top Dressing Existing Gardens Trees, Shrubs, Roses, and Fruit Trees 

• Use Tui General Garden Fertiliser, Rose, Citrus, Acid, or Lawn as appropriate.
• Ican Real Blood and Bone
• An alternative is Tui Sheep Pellets

For Vegetable Garden and Flower Beds

• Use Ican 100% Organic Vegetable Food – the perfect blend of nutrients for fruiting and flowering. Mix this into the soil prior to planting.
• Or liquid fertiliser such as Ican OceanGrow Organic or Ican Fast Food.
• An alternative and also very good as a top dressing is Novatec. Novatec is approximately 2.5 times more concentrated and can therefore be used more sparingly. 

Pots and Containers - All plants

• Use Osmocote once or twice a year.
• Liquid feed with Ican Fast Food.

Lawns

• Apply Tui Lawn Food three or four times a year. Be careful to apply evenly to avoid burning and temporary brown patches.
• Use Scotts Lawn Builder for a controlled release feeding over a longer period of time. Great for sandy soils from which a soluble fertiliser could be quickly leached.

House Plants - All plants

• Use Osmocote once or twice a year.
• Use soluble or liquid foods as a boost as required - iCan Fast Food is a great food for House Plants.

Liquid Feeding

Liquid feeding of plants is useful for giving plants an extra boost. It is particularly effective for plants which are lacking thrift or recovering from a shock eg. at transplanting time for seedlings, or for boosting yields eg tomatoes. Liquid feeding should be repeated 4 or 5 times at 2 weekly intervals. Good liquid feeds are ican Fast Food (for all plants) and ican Oceangrow which is a fish based feed particularly good for Roses, but it is too smelly to use indoors. 

Organic Manures

These are usually based on animal manure and in addition to supplying nutrients, they have a beneficial effect on soil structure, as well as supplying nutrients. Examples are ican 100% Organic Vegetable Food or Tui Sheep Pellets.

Lime

There are three types of lime

• Garden Lime contains Calcium carbonate
• Dolomite Lime contains a mix of Calcium carbonate and Magnesium carbonate
• Gypsum is Calcium sulphate.

Garden Lime and Dolomite lime are both alkaline and are used to

• Condition clay soils
• Reduce acidity
• Provide calcium
• Improve the availability of phosphate in the soil.

Gypsum is neutral and is used to

• Condition clay soils
• Provide calcium
• Improve the availability of phosphate in the soil.
• Being neutral it does not affect acidity

Gardens benefit from an annual dressing of Lime Dolomite or Gypsum. It improves the condition of clay soils and improves the availability of phosphate. This means that the other fertilisers applied will work better. However don’t over apply. Excess Dolomite application can lead to an over alkaline soil which suppresses potassium and other nutrients.

Use Gypsum rather than Lime or Dolomite on acid loving plants such as azalea, camellias and rhododendrons, and lawns.

Gypsum is a better, safer alternative unless the soil is known to be acid.