Tuesday, 16 June 2015

Organic Fertiliser, Seaweed or Fish for the Garden?

I decided to write this post after visiting my local hardware and garden shop to buy some products to feed our vegetable garden and citrus trees. I think that our veggie garden needs more regular feeding since we often have yellowing or slow growing crops despite putting a lot of effort into building up an organic rich soil. I figured the only way to work out if it would help is to give it a go and see if it improves. Please note that I bought these products a couple of months ago but it has taken me some time to get around to researching and writing about it.

Clearly the need to feed plants is post worthy in itself. I am cautious about over feeding plants since I am aware that excess runs off (although our soil structure is good in the vegetable beds so it should retain quite a bit) and drains quickly through the sandy soils in Perth, straight into the waterways. The motivation for this post, however, came more from the terrible information that I was given when buying the products.

Our conversation went a little like this.

LL: "I think I need to feed my plants more regularly. I definitely want seaweed extract and I want to try a fish emulsion. Is this a fish emulsion? (holding product I was looking at out to show him). Can you recommend a fertiliser that would work well with them?"

The salesman pointed to an organic fertiliser product: "This is good to use and yes, that is a fish emulsion."

LL: "What are each of these products doing?"

The salesman sized me up holding my baby in my arms: "The seaweed and fish emulsion are like having a... (he paused to find the right word)... cup of tea. You could use them everyday and it would be fine. The directions say to use fortnightly but you can use them as often as you like. The fertiliser is stronger and you wouldn't want to use that more than fortnightly or it will be too much for the plants."

LL: "Really? But what is the difference?"

Salesman (clearly assuming I have no brain cells left since I was a mother): "You can use the fish emulsion and seaweed as much as you like and it will help the plants but don't use the fertiliser too often".

End of conversation. Hmm... I'm not sure that really gave me any new information. Like drinking tea for the plants? Are you kidding me? Why did I get the impression that if I was a guy he would have said it was like having a beer at the end of the day? (Note: I quite enjoy a beer at the end of a busy day but I am also a huge fan of tea too.)

Anyway, I decided I wanted to find out what these products actually do and thought that I might not be alone. After I started looking into it I realised I know so little about this topic. Here is a bit of basic information about liquid fertilisers to get into the right headspace:

What are the benefits of using organic liquid fertilisers?

Liquid fertilisers have dissolved nutrients in a solution (liquid!) that can be applied to a plant through spraying on their leaves or applying to the soil. Since the nutrients are already dissolved the plant can absorb them immediately. Here is a link to a great article I found on Organic Gardener that discusses liquid fertilisers in a lot more detail. Organic liquid fertilisers also improve the soil life and cycling of nutrients for plants.

The flip side of this is that if you use too much liquid fertiliser the plant will not absorb the nutrients and they are likely to flow out of the soil into the surrounding environment. The trick is to know when your plant needs to be fed. Unfortunately this varies depending on your soil type, soil structure, plant type, the time of year and other factors. Here is a helpful article I found on Sustainable Gardening Australia that talks about when to feed your plants. I'm sorry to say that there are no simple answers on this. All we can do is to try and learn what the plant is likely to need and then experiment to see what works in our own gardens.

As I said above, all of our productive plants were showing signs that they need some extra food, mainly due to yellowing leaves. They were also getting infested with aphids and other pests all of the time and I was aware that regular seaweed treatments could help them to become more resilient. Hence the trip to the shop to buy these products and see if I could improve our crops from their use.

Seaweed treatments

The research I have done on using seaweed extract in the garden suggests that it is beneficial for plants.  Seaweed concentrate has very low or no nitrogen and phosphorous in it so it is not a fertiliser. Benefits are believed to come from growth regulating hormones as well as other compounds that stimulate healthy soil and a positive immune response in plants. This helps them to stay healthy and withstand problems, such as extreme temperatures or pests.

Since seaweed isn't supplying nitrogen or phosphorous but it is helping the plant to remain healthy it is commonly referred to as a "plant tonic". I think Mr Salesman might have been comparing the plant tonic concept to having a cup of tea. I guess I can begrudgingly score him a point for that comment. I will just as quickly remove his point, however, for stating that the product can be applied as often as I want to without harm. Although the plant might not show negative effects from liberal and frequent application (with no regard for instructions) I frown upon it for these reasons:

1) It is waste of resources and money
2) It is unnecessary (see point 1)
3) What is not used will surely run off into waterways where it is not going to necessarily be beneficial

Fish Emulsion and Fish Fertiliser Treatments

Fish emulsion or fertiliser seems to be a highly variable product. Fish emulsion has natural ratios of nitrogen(N): phosphorous(P): potassium(K) of approximately 4:1:1. These ratios reflect a natural breakdown of fish materials which can be used as an organic fertiliser in the garden. There are other products marketed as fish emulsions or fertilisers but they have higher ratios of nutrients (e.g. 10: 2: 6), which suggests they have been chemically altered and hence are manmade or inorganic. As discussed in the Sustainable Gardening Australia article the nutrients provided through both processes are the same but the quantities and benefits to the soil vary between products. Manmade products are likely to have chemicals that could inhibit microbes in the soil and thus make it less healthy.

Fish emulsion has been described as both a fertiliser and a plant tonic. Nitrogen, phosphorous and potassium are all essential nutrients that plants need in large amounts to remain healthy and grow. Since fish emulsion contains these ingredients it is (as stated above) an organic fertiliser. The "plant tonic" relates to the organic nature of the product improving soil health and stimulating microbe activity. It is providing a service similar to the seaweed extract but with different minerals and compounds since it has originated from fish.

For fish emulsion Mr Salesman has a further three points subtracted. One because he called fish emulsion a plant tonic, which is only half right. It is also a fertiliser. Secondly he also loses a point because he advised to use it as often as I like (see the three points above as to why I frown upon this advice). Most importantly, however, he didn't let me know that the type of fish emulsion I was planning to buy (I specifically asked him if it was fish emulsion since the information wasn't clear from the labelling) had inorganic nutrients added, with a fertiliser ratio of 10: 2: 6. I have only found that out through doing my research. Had I bought the "organic" version of the product it would have had ratios similar to those listed above. Salesman is currently on minus 3.

As a side note, I came across an experiment comparing the benefits of seaweed and fish treatments on lettuces, conducted by Tino from Gardening Australia. Tino found fish emulsion to be the best choice for lettuces since it is high in nitrogen, which promotes leaf growth. Lettuces that received seaweed treatments were very healthy and pest free, however, so Tino concluded that he would like to try a combination of both fish emulsion and seaweed. To read about Tino's experiment follow this link.

Organic Fertilisers

The organic fertiliser that Mr Salesman recommended has a nutrient ratio of 3: 0.1: 3 for N: P: K. It is  made from a fish fertiliser and soil conditioner. Now that I have done my research I realise that this product is basically the same as what I should have expected from the fish emulsion that I bought. I think the elevated potassium is from the soil conditioner in the solution.  Here is a bit of information about organic sources of potassium in case you are interested.

It is good to know that this is a good product but annoying to find out that I didn't need the "fish fertiliser" that I bought as well. I guess I can once again begrudgingly appoint one point to Mr Salesman for recommending this product, putting him on a generous minus 2.


The main points that I am taking from this are:

1) Seaweed extract is really good for encouraging healthy soil and plants
2) Look at the nutrient ratio in any fertiliser that you are buying and remember if it is above approximately 4: 1: 1 then it is likely to have inorganic products in it
3) Don't expect to get good information from the salesman at my local hardware and garden shop

I am going to throw out the fish fertiliser since it has elevated levels of nutrients that are likely to be promoting lush growth that is more easily attacked by pests. It might also be damaging my soil health due to the artificial chemicals in it.

I am going to continue using a combination of the seaweed extract and organic fertiliser at below recommended dosage (about 20 ml instead of 30 ml) as close to fortnightly as I can manage.

Mr Salesman clearly did a hopeless job of addressing my concerns, most likely because he has no idea about all of the points that I have made above. I will do my best to research these things before going and buying products in future.

Have I helped you to decide whether you want to use organic fertiliser, seaweed or fish for the garden? Please share your experiences and thoughts

I have managed to just finish this in time to join IBOT with EssentiallyJess

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