Container gardening Potting Mix and Fertilisers for GreenSmart Pots


Most garden soils are too heavy and are unsuitable for container gardening. Soil-less organic potting mix works best and should be both lightweight and moisture retentive.

A good quality organic potting mix should have an air-filled porosity of at least 15% with a pH reading between 5.0 and 6.5 which is satisfactory for most plants, whereas the desired pH range is 6.5 – 7.0 for most vegetable plants.

Porosity is one of the most important properties of a potting mix when container gardening. It is the space available within a mix for water, air or root growth. Small pores contribute to water retention whereas large pores promote aeration.

Add dolomite and lime to the potting mix to neutralise the acidity and maintain a balance between Calcium and Magnesium. A mix of balanced fertilisers needs to be added to the potting mix before planting. Periodic applications of fertilizers are recommended throughout the growing period. Note: Reproductive crops do not need high levels of calcium and low levels of phosphate. I find that Yates Dynamic lifter is a great organic fertiliser to add when container gardening. It is based on chicken manure and seaweed.



Acidity and alkalinity of soil is measured by what is known as the pH level, which measures from 0-14.  It is also a measure of the capacity of the soil to retain positively charged nutrient ions

The Neutral point on the scale is pH 7.  Any reading below 7 indicates that the soil is acid. Readings higher than 7 show that the soil is alkaline. Soil pH levels specifically affect plant nutrient availability by controlling the chemical forms of the nutrient.

Preferred acidic or alkaline level in the growing medium varies according to the type of plant. Incompatible pH levels affect the ability of nutrients to be plant available in the growing medium. Adjust the pH level to suit the requirement of the plant to makes the minerals and the nutrients plant available. Soil pH and moisture can affect the solubility of nutrients and the ability of plant roots to absorb nutrients.

A pH test of your growing medium is important to adjust the compatible pH range for the plants you intend to grow. Although most vegetables do best in a slightly acid soil, there are some vegetables that prefer alkaline conditions. The ideal pH level, controls root activity and fertiliser availability. For instance increasing pH reduces availability of phosphorus and certain micronutrients for vegetable production. With the desired pH level, right temperature and moisture, the nutrients will be readily available for the plants, with increase activity of the microbial populations in the soil.


Container gardening

Container gardening

Container gardening 

Raise pH with dolomite or lime: Add 1 to 1.5 grams of dolomite per litre of potting mix to raise pH of the top 10cm by about 1 unit.

Lower pH with sulphur: Add 0.3 grams of sulphur per litre of potting mix to lower pH of the top 10cm by about 1 unit.

Readings higher than 7 show that the soil is alkaline and lower reading indicates that the soil is acid. The higher the pH reading, the more alkaline and oxygen rich the fluid is. The lower the pH reading, the more acidic and oxygen is deprived in the fluid.

Most vegetables grow best in container garden media that have a pH range of between 6.0 and 7.0. At this pH range most nutrients that plants need are readily available. Excess acidity the common problem confronted by many home gardeners. This imbalance is remedied by liming. It is advisable to invest in an inexpensive pH testing kit. These kits (not the probe) can be purchased from most garden centres.

Dolomite and lime is applied to soil in order to change the soil from an acid to a near neutral condition. The amount of dolomite or lime added to the potting mix is only one of factors that affect the growing medium, as the crop is grown. However, fertiliser that contains ammonium or urea has an acidifying effect, causing a decrease in pH after repeated use. When a crop requires an acidic condition, Elemental sulphur and organic material can be used to lower soil ph. As pH levels in the soil begin to drop below 5.0, toxic elements such as aluminium and manganese become more available to plants. Essential elements such as nitrogen, potassium, phosphorus, and others become less available to plants. Beneficial biological activity is hindered as well. As pH levels rise above 7.0, elements such as phosphorus, copper, and zinc are less available.

But before attempting to adjust the pH reading when container gardening, you should first conduct a test to determine your current ph. If your potting mix is alkaline, you can lower your potting medium pH or make it more acidic by using several products. These include sphagnum peat, elemental sulphur, aluminium sulphate, iron sulphate, acidifying nitrogen, and organic mulches some types of fertilizers can help to acidify the potting mix and most of them are safe to apply. Acidifying fertilisers include ammonium sulphate, phosphate, phosphate, urea, and ammonium nitrate.

What is the difference between lime and dolomite?















Container Gardening Seasonal Growing Chart (with optimum pH levels & temperature)


Type of Plant Optimum temperature range +/- 3°C Seed Germination pH in the range Season Days to Germination
Artichokes 15°C -25°C 15°C -25°C 6.5-7.5 Intermediate
Basil 18°C -30°C 18°C-25°C 6.0-7.0 Warm Season 7-15
Beans 20°C –24°C 15°C –26°C 6.0–6.8 Warm Season 7-10
Beetroot 15°C -23°C 10°C –26°C 6.5-7.5 Intermediate 7-10
Bitter gourd 24°C -27°C 18°C –27°C 6.0-7.0 Warm Season 5-7
Bok Choy 13°C -21°C 10°C -18°C 6.0-7.5 Cool Season 4-7
Broad beans 15°C -24°C 24°C –30°C 6.0-7.5 Cool Season 7-10
Broccoli 15°C -23°C 10°C –25°C 6.0-7.5 Cool Season 4-7*
Brussels Sprouts 15°C -21°C 20°C –25°C 6.0-7.5 Cool Season 5-7*
Cabbage 15°C -23°C 10°C –25°C 6.5-7.5 Cool Season 5-7
Capsicum 18°C–25°C 18°C –29°C 5.5-6.5 Warm Season 7-14*
Carrot 16°C -23°C 10°C -23°C 6.0-6.8 Intermediate 10-14
Cauliflower 15°C -23°C 10°C-25°C 6.0-7.5 Cool Season* 5-10
Celery 15°C -20°C 15°C-21°C 6.0-6.5 Intermediate 12-20
Chilli 15°C-29°C 18°C –29°C 6.0-7.5 Warm Season 4-7*
Chives 12°C -24°C 15°C -21°C 6.2-6.8 Cool Season 14-21
Climbing Beans 15°C -24°C 24°C –30°C 6.0-7.0 Warm Season 7-10
Coriander 16°C -20°C 20°C -25°C 4.5-8.0 Intermediate 7-14
Corn 15°C –29°C 10°C –20°C 6.0-6.8 Warm Season 4-6
Cucumber 18°C -24°C 15°C -29°C 6.0 -7.0 Warm Season 5-8
Eggplant 21°C –29°C 23°C –29°C 6.0. -6.8 Warm Season 6-13*
Endives 10°C -23°C 20°C –22°C 5.5-6.0 Intermediate 7-14
Garlic 12°C -24°C 13°C -24°C 6.2-6.8 Intermediate 7-10
Kale 8°C –24°C 10°C –24°C 6.2-6.8 Cool Season* 10+12
Kang Kung 23°C -30°C 25°C -30°C 6.0-7.0 Warm Season 14-21
Kohlrabi 15°C -24°C 15°C –26°C 6.0-7.5 Cool Season 7-14
Leeks 13°C -24°C 13°C -24°C 6.0-7.5 Intermediate 5-14
Lettuce 8°C -18°C 5°C –20°C 5.0-6.0 Intermediate 3-4
Malabar Spinach 15°C –24°C 23°C –30°C 6.0-6.7 Warm Season 7-10
Okra 21°C –29°C 21°C -29°C 6.0-6.5 Warm Season 7-14
Onion 10°C -24°C 10°C –24°C 6.2-6.8 Cool Season 5-14
Pak Choy 10°C -20°C 18°C –23°C 6.0-7.5 Cool Season 7-14
Parsley 10°C -24°C 10°C -24°C 6.0-7.0 Intermediate 14-17
Parsnip 12°C -21°C 10°C –21°C 6.5-7.0 Intermediate 10-15
Peas 10°C -23°C 5°C -23°C 6.0-7.0 Cool Season n* 7-10
Potato 12°C -24°C 22°C –24°C 5.2-5.5 Cool Season 5-7
Pumpkin 18°C –24°C 21°C -26°C 5.8-6.8 Warm Season 10-14*
Radish 10°C -23°C 10°C –23°C 5.0-6.0 Intermediate 4-6
Rhubarb 15°C -30°C 20°C –25°C 5.5-6.5 Intermediate  (Crowns)
Shallots 12°C -24°C 13°C -24°C 6.2-6.8 Cool Season 5-14
Silver beet 12°C -23°C 10°C –26°C 6.0-7.0 Intermediate 10-14*
Snow Peas 10°C -21°C 12°C –21°C 6.5-7.0 Cool Season * 7-10
Spinach 15°C -18°C 10°C –21°C 6.5-7.0 Cool Season 12-15
Spring onions 10°C -23°C 15°C –23°C 6.0-7.0 Cool Season 5-14
Strawberry 15°C -30°C 18°C –23°C 5.8-6.5 Intermediate Bare root
Tomato 18°C–26°C 18°C –29°C 6.0-6.8 Warm Season 6-10
Turnip 10°C -23°C 10°C -23°C 6.0-7.5 Cool Season 3-7
Water Melon 21°C –30°C 26°C -30°C 6.5-7.5 Warm Season 3-5*
Zucchini 18°C–29°C 21°C–30°C 5.8-6.8 Warm Season 6-10


Please note table references:

 = Cold hardy and frost hardy

* = Vegetables that tolerate frost when the plants are in their early stages but are damaged by it when near maturity.

= Vegetables that are frost tolerant and cope with a higher temperature range of 13 – 24°C



Organic fertilisers are “natural” derived from decaying matter – decomposing plants or the food that have been digested by animals. Organic manures feed the microorganisms in the growing medium which convert organic nutrients into a form which can be absorbed by the roots of plants. They are slow acting and improve the soil’s condition by releasing plant nutrients slowly. For organic fertilisers, use processed materials such as bone meal and dried blood, animal or poultry manure and seaweed. Some liquid fertilisers are derived from seaweed and humus extracts. Organic fertilisers will contain everything your plants require for container growing.

The function of the three main elements:

Plant life depends on Macro nutrient elements. The primary Macronutrients -commonly known by the abbreviations NPK, which are essential in large quantities for plant growth, are: Nitrogen, Phosphorous and Potassium and the secondary Macronutrients are Calcium, Magnesium and Sulphur.

(N) Nitrogen   

Nitrogen is an important nutrient for the plants. It promotes the growth of leaves and  stems.

(P) Phosphorus

Phosphate is necessary to carry nutrients into young plants for vigorous root development and also plays a part in the growth of plants and the production of flowers and seeds. Too little phosphorus can result in stunting, but too much can cause bitter flavour in crops.

(K) Potassium

Potassium or potash is vital for maintaining growth and for providing plants with resistance to disease. It contributes to the building up of starches and sugars in vegetables.  Severe deficiencies in vegetables can appear as deformed, stunted or yellow leaves, weak stems and premature fruit drop.

The other trace elements which are taken up by plants in small quantities are:

Magnesium, Manganese, Calcium, Iron, Boron, Zinc, Molybdenum and Copper. Organic growing often focuses on the practices that are allowed or prohibited by organic certification standards. However trace elements such as copper, iron and zinc are generally permitted to be applied as chelates if needed. Boron can be applied as borax or solubor. Commercially available garden lime often contains quantities of some trace elements. The uptake of trace elements to the plants requires a high level of calcium and phosphates.


Using organic or inorganic fertilisers for growing vegetables is an individual choice. Most inorganic fertilisers are chemicals or manufactured and concentrated. Some are derived from mineral deposits. They are used in much smaller quantities, and the release of nutrients to plants is more rapid. However they are pollutants which can cause a die off of and population change of soil microbes. Concentrated fertilisers are usually applied before or at time of planting and should be thoroughly incorporated into the top 10cm of the soil or potting mix. Side dressings of additional fertiliser or the application of supplementary foliar fertilisers which also contain trace elements needed by the plant, may be required during the growing period. Concentrated fertilisers are sold in both solid and liquid form and this must be diluted before use. It is advisable to follow manufacturer’s instructions.


The mix of fertiliser combination and additive that can be used with the organic potting mix for a large 40L capacity pot is:

  • 40L of Organic potting mix
  •  1 handful of lime
  •  1 handful of Dolomite  (Contains calcium and magnesium)

            Organic potting mix can be acidic with a pH reading of 5.0-5.5. Dolomite and Lime  neutralise acidity to a desired pH range of 6.5 – 7.0 to grow most vegetables.  (Do not add dolomite or Lime for those vegetables which need acid conditions).  

  • 3 handfuls of processed Chicken manure/Dynamic lifter                                                       Extremely high in nitrogen and should be used sparingly. . Nitrogen is used as an accelerator to control growth and ensure a good balance between leaves and fruiting
  • 1 handful of Blood and Bone ….               slow releasing nitrogenous manure along with phosphorus and calcium.


There are no comments

Your email address will not be published.