Foliar Spray vs Slow-Release Fertiliser

There are two ways to feed plants and gardeners are often divided as to which method is the best. Some swear that foliage fertiliser sprays are the most efficient and effective method at delivering nutrients to a plant. Others, especially the permaculture set, are adamant that ground based fertilisers are the better of the two.

Well, it may just be that both are essential. In fact, using both foliar spray and slow-release fertilisers may be an even better outcome for you plants.

We’ve been re-indoctrinated to believe that the soil in which a plant grows is the most important element in our garden’s health. And quite rightly so. However, this has come at a cost because our perceptions of foliar spray fertilisers has become more negative.

We know and understand that plants receive most of their nutrients through their root system. If the soil is healthy and well nourished then the plant can feed well and grow with a minimum of fuss and problems. Even pests and disease are less likely to trouble our plants.

What we may not know is that using foliage fertilisers may actually increase that intake – and exponentially as well.

Here’s how the process works;

By applying a foliar fertiliser directly to the leaf, it increases the activity in the leaf, at the same time increasing chlorophyll and thus photosynthesis. Because of this increased activity, it increases the need for water by the leaf. In turn this increases water uptake by the plants vascular system, which in turn increases the uptake of nutrients from the soil.

So, in actual fact while we need to maintain the nutrients in the soil the use of foliage fertilisers can increase their effectiveness and the plants efficiency at using them.

How to use foliar spray fertilisers

Foliage fertilisers always retail in liquid form, or at least in powder form that requires them to be dissolved in water. This is the best way for your plants to draw their nutrients from the fertiliser.
Most plants will only require a slow-release fertiliser application once at the start of each growing season. However, foliage fertilisers can be applied much more often and this depends on the type of plant grown.

  • Perennials – should only require a foliar spray every 6-8 weeks during their flowering or growing season.
  • Annuals – are much heavier feeders because their whole growth needs to be completed from seedling to producing plant within one growing season. Therefore, their fertilising needs are heavier and they will require a foliage fertiliser every 3 weeks at a minimum.
  • Vegetables – on the other hand, vegies need even more and should be fed through their foliage every week during their production season. This will stave off any pest and disease problems and increase the yields of your vegetables.
  • Fruit – if you compare the speed of most fruit trees from flower to produce you will notice that it is considerably slower than say, a carrot crop which can be ready within 12 weeks. Therefore, there is less need for fruit trees to be fertilised and these should be treated the same as your annuals.

With foliar spray fertilisers, the key nutrients you want to impart are potassium and phosphorous – in that order. Nitrogen, which is responsible for leaf growth, is your least desired element as the foliage will grow well to the detriment of fruit and flowers.

One of the most popular foliar spray fertilisers is fish emulsion. However, it’s not the best as most fish emulsions usually have a ratio of 5:1:1 which is great for growth to the exclusion of blooms and fruit. You would be better finding a liquid fertiliser with an NPK ratio of 1:1:1.5.

So, the final outcome is that both are necessary. We need to feel our soils with slow-release fertilisers, compost and other organic materials but we should also be feeding our plants with foliar sprays to help them grow. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Additionally, we participates in various other affiliate programs, and we sometimes get a commission through purchases made through our links.