The Best Tomato Fertiliser in Australia (and How to Use it)

Avid gardeners know that there’s nothing better than ripe, juicy, home-grown tomatoes.

Spring has finally arrived and it’s tomato-growing season here in Australia.

Apart from ensuring that your tomatoes get plenty of sunlight and water, you also need to feed them if you want to get the most prolific crop.

Which fertiliser is best for tomatoes?

fertiliser in garden | Fruit & Vegetables

For good fruit production, you want a fairly balanced fertiliser that contains good amounts of potassium.

Avoid fertilisers that are high in nitrogen and with little potassium because this will create plenty of green growth but not enough flowering and fruits.

In fact, if you’ve prepared the soil well beforehand and applied a good amount of organic matter such as matured compost, your tomato plants really shouldn’t need any further application of nitrogen.

For a natural approach, a small application of chicken manure once a month will ensure that your tomatoes grow well and produce plenty of fruit.

Alternatively, there are plenty of good commercial fertilisers available designed especially for tomatoes that you can buy at Bunnings or your local garden centre. 

Some examples include:

As you can see, there’s a wide range of fertilisers available with varying N:P:K ratios. All of the above fertilisers are perfectly adequate for growing good tomatoes.

But if I was to choose the best according to the N:P:K ratios, I would recommend either the Thrive liquid plant food or the Searles 5 in 1.

With these two products, you’ll notice that the ratio of potassium to nitrogen is equal or higher. This means that they’ll be much better for promoting good fruit production.

A brief guide to N:P:K ratios

N – The first number represents the amount of nitrogen in the product. Nitrogen promotes vigorous leaf growth and deep greening of plants, but too much can cause burning of foliage.

P – The second number represents the amount of phosphorus in the product. Phosphorus promotes root growth and flowering.

K – The third number represents the amount of potassium in the product. Potassium helps plants withstand stress and promotes overall hardiness and disease resistance. It can also help with flowering and fruiting.

What fertiliser makes tomatoes bigger?

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The secret to large tomatoes is potassium. This is why I recommend a fertiliser high in this nutrient and lower in nitrogen.

However, you can actually purchase sulphate of potash separately and add it as a supplement. This nutrient has the added benefit of increasing the disease resistance of your tomato plants.

But, remember that you only need to use a small amount so follow the directions on the pack carefully.

How to use fertiliser on tomatoes

fertiliser | Fruit & Vegetables

If you’re using a granular or pelleted fertiliser, you’ll only need to apply this once during the growing season as most of these are slow-release.

This means that they’ll release the nutrients to the roots of the plants as they need them.

Generally, you want to spread a small amount of granular or pelleted slow-release fertiliser on the soil around the base of each plant.

You can fork this in but do this gently so as not to disturb the roots of the plants. Alternatively, it’s better to just water it in with a good soaking.

However, if you prefer to use a liquid fertiliser, then you can apply this every 2 to 3 weeks by mixing it with water in a watering can and applying it to the plants. Liquid fertilisers tend to be used by plants almost immediately.

Homemade tomato fertiliser

banana skins | Fruit & Vegetables

If you prefer to steer away from commercial fertilisers and give your tomatoes a natural boost then there are various things you can do.

One of my favourite ways to give my tomatoes a boost is by using banana skins. These are naturally high in potassium and will break down in the soil to feed the plants.

You can place a piece of banana skin in the bottom of the hole when planting your tomatoes. I usually do this when planting roses as well.

You can also make banana tea liquid fertiliser by steeping the banana skins in water for a week or so and then using the liquid to feed your plants.


Is Seasol good for tomatoes?

Yes, Seasol can be beneficial for your tomato plants, especially when the plants are young. This is because Seasol will promote excellent root development and help to strengthen the cells in the growing plant.

Can tomato fertiliser be used for other plants?

Tomato fertiliser can be used successfully for all fruiting and flowering plants because it is higher in potassium which promotes both fruiting and flowering. Therefore, you can use this on other fruiting crops such as capsicum, cucumbers, and squash, and flowering plants such as roses, azaleas, and camellias.

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Annette Hird

Annette Hird is a gardening expert with many years of experience in a range of gardening related positions. She has an Associate Diploma of Applied Science in Horticulture and has worked in a variety of production nurseries, primarily as a propagator. She has also been responsible for a large homestead garden that included lawn care, fruit trees, roses and many other ornamental plants. More recently, Annette has concentrated on improving the garden landscape of the homes that she has lived in and focused a lot of energy on growing edible plants as well. She now enjoys sharing her experience and knowledge with others by writing articles about all facets of gardening and growing plants.


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