The right mix

When you walk down the potting mix aisle of your local hardware store or garden centre, it will quickly become obvious that there's an enormous range from which to choose.

Not just different brands, like Osmocote or Debco, but a rainbow assortment of coloured bags, each one seemingly designed for a particular plant, group of plants or situation.

For example, there are mixes for:

  • Bulbs
  • Bonsai
  • Cacti
  • Orchids
  • Vertical Gardens
  • Vegetables

The list is endless! So which do you choose, and why?

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light-bulb-icon@2x.png Plants have differing needs

It's estimated there's close to half a million different plant species found on Earth. And that's not counting the hundreds of thousands of varieties that have been bred from them!

Plants occur naturally over an extraordinary range of climates and soils - from the frozen polar regions to the tropics - so it's important to recognise this when you're trying to grow plants in pots, baskets, barrels or vertical/wall gardens at home.

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For them to survive, you should naturally have or create environments that resemble those they come from.

A tropical hibiscus will happily grow outside in Brisbane, for example, but in Melbourne or Hobart you will almost certainly need a green house or glassed-in veranda to reproduce the warmth and humidity it requires.

The same principle applies to potting mixes - you need to provide plants with mixes that closely resemble the soils of their natural habitats - not only the texture of the mix, but the acidity/alkalinity (pH) and available nutrients.

light-bulb-icon@2x.png 'Horses for courses'

Potting mixes are usually formulated to reproduce as closely as possible the soil conditions that plants prefer. While there are all purpose mixes that will be quite suitable for a vast array of different plants, there are some plants that require special mixes to meet their very specific needs.

For example, cacti and succulents are most often (but not always) found in dry, arid regions. The soil of these habitats is often very sandy or gravelly with little organic material or nutriment in it. When it rains, water soaks in and quickly disappears deep into the soil.

horses-for-courses.jpg

A cacti and succulent potting mix should therefore:

  • have a high percentage of coarse sand or grit
  • be free draining
  • be relatively nutrient-deficient

The same applies to other plant groups:

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Top Tip

Take the time to look at the multitude of bagged potting mixes available from your retailer to see what they're designed and recommended for. Consider this information in relation to the plants you have and buy accordingly.

light-bulb-icon@2x.png What if I've bought the wrong mix?

In most instances, choosing the wrong mix probably won't have a major impact. That's because the variations in formulation between them are minimal - the major differences being in the type of fertiliser added and how well the mix holds water or drains.

You'll only run into trouble if you use a mix that is totally unsuited to the plant you have.

By way of example, you've potted up carnations (which prefer a soil pH of 6.75 - 7) into a rose and azalea mix with a pH of 5.2! The carnations will not grow well, may yellow and will certainly not produce the abundance of flowers you would expect.

If you pot a cactus into an all purpose mix that doesn't contain added grit and is high in organic content and nutrients, it's likely it will sulk. It may rot around the base and fail to flower - it certainly won't grow as you would like it to.

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Usually the best way to overcome these problems is to replace the mix with one that has been designed for the plants you have.

You could try one or more of the following:

  • add some coarse washed sand to 'open' the mix up so it drains more freely
  • add garden lime (at the label rate) to raise the pH if the mix is too acid
  • mix in compost to increase water-holding and organic content
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Top Tip 

If you've bought the wrong mix but only discovered your error when you're ready to use it, you may be able to adjust it to make it more suitable.

Tips, tricks & advice

Choosing the right pot

Pots come in all shapes, sizes and materials. On trend or functional, a pot needs to be the right size for the plant

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How to pot a plant

Gardening in pots can be fun and rewarding. The secret to success is knowing how to pot up a plant!

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