Ruud Kleinpaste: Feeding plants

Three reactions to the concept of “feeding your plants”:  

1. Plants feed themselves through Photosynthesis (you don’t need to feed your plants!)  
2. They’ll pick up elements in the soil that they need for growth and development – nobody feeds the plants in a native forest. 
3. What’s scientifically needed for our gardens is a soil test that indicates which chemical elements are lacking in soil. 

This is about the Science of Fertilisers. 

This is the time of the year when soil temperatures are the best for plant growth. Roots work over time to extract minerals, dissolve them in water, and transport them through the phloem bundles to the leaves of plants, where photosynthesis puts it all together and creates carbohydrates and chemicals that allow cell-elongation (growth).  

Plants use three main elements for bulk growth “food”: Nitrogen, Phosphorous and Potassium (K), which are generally known as NPK (their chemical symbols).  

N is used to make green stuff: leaves and Chlorophyll (LAWNS, LETTUCE, SPINACH, HEDGES). 

P is good for root development and plant health (CARROTS, PARSNIPS, POTATOES, etc). 

K (potash) is for sex: flowers and fruits (TOMATOES, APPLES, STRAWBERRIES, FLOWERING PLANTS). 

Other elements needed for a plant to function are needed in much smaller quantities:  

Mg (Magnesium), S (Sulphur), Ca (Calcium), Cu (Copper), Fe (Iron), Zn (Zinc), Mn (Manganese), and a heap more of those minor “trace elements”. 

There are a few different types of fertilisers:  

1. “General” Fertiliser – for general growth. Usually something like N-P-K 7-3-6 or 12-4-13 (note how Phosphorus is usually less than the N and K). 
2. Potato fertiliser: N-P-K 3-9-6 also good for carrots and parsnips. 
3. Tomato or rose fertiliser, which is usually higher in potash (K): N-P-K  3-4-9. This helps to stimulate flower and fruit growth. 

Of course you can always use the general fertiliser (which tends to be highest in Nitrogen) and simply add a few handfuls of Superphosphate (P) if you grow root crops, or handfuls of Sulphate of Potash (K) if you want to up the dose of K (potash) for flowers and fruit.  

Organic fertilisers usually have lower concentrations of elements, and they are often less prone to fertiliser run-off into water courses. Chicken poo (a “natural” organic fertiliser) has a high content of Nitrogen which can burn plants – I would always send it through a cycle of composting before use. 

I use General fertiliser on my young tomatoes to get them growing up and create a strong climbing vine before the flower buds are formed. Once they start flowering, I assist the plants with more potash to keep on making fruit – I just switch to a higher potash fertiliser such as Wet&Forget’s Seaweed Tea.  

Seaweed Tea and Seafood Soup were designed to quickly fertilise lawns and large amounts of vegetables. It has this clever system of watering your plants and enriching the soil. I use the contents of Soup and Tea in watering cans – often in a very mild (or “weak”) solution. In the tunnel house I do this almost every day to water the tomatoes; with small amounts of tea or soup I add a little bit of fertiliser with every watering -  works brilliantly! 

 

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Episode Transcript

Speaker 1 (00:07):
You're listening to the Saturday Morning with Jack Tame podcast
from News Talks at be.

Speaker 2 (00:13):
A Man in the Garden is rude? Climing passed? Rude?
I started the show this morning by explaining that I've
just been jiggling my strawberries because the strawberries are my
place are looking excellent right now. But I've been going
out each morning just as I leave the house, and
you know, just repositioning them so that they don't get
too much contact with the ground or anything. I've got
straw underneath them, but just in case there's any moisture

(00:33):
or anything like that. So I've been looking for a
new term because I think jiggling strawberries doesn't quite work.
So Vicky, you sent me a note. She said it
could be strawberry jostling, which I quite like. Joscelyn, yeah,
or just turning your strawberries. Do we say? Is there
an official term in the gardening world, Not that I.

Speaker 3 (00:52):
Know of, but you've got it right. What I would
say is I would put it on too on dry
what do you call it, grass clippings or something like that,
so to not have to me in contact with a
moist soil.

Speaker 2 (01:06):
No, So I've got I've got pea straw underneath it.
I've put straw yes, yes, but it's still I just
am kind of paranoid about it. So I still go
out there and just you know, just turn the never
so slightly, you know.

Speaker 3 (01:18):
Well, then your word would be peace strawing.

Speaker 2 (01:21):
Yes, maybe peace strawing, peace drawing my strawberries, yeah, peas strawberry.
I don't know. Anyway, it is nice to see them.
I'm not sure how they are your places yet, but
we've had such hot weather in Auckland over the last
couple of weeks that I think they're just just the
first strawberries of the season, just coming through.

Speaker 3 (01:40):
Yeah, be careful though, don't get too hot, you know
what I mean, if you can handle that. But also
the point is that you need to have them literally
in a drier condition then yeah, so the peace strawing
is not a bad idea.

Speaker 2 (01:53):
Yeah, very good. Anyway, you're focusing on feeding plants the
right stuff at this time of year, because.

Speaker 3 (01:59):
Yeah, yeah, first of all, I don't like the word
feeding because you don't feed your plants. I mean, gosh,
who goes out into the forest and feeds the trees?
You know? Yeah, that's the whole point. So the point.
But then again I get a lot of people on
talk back too that are complaining that there's not enough
fruits on the trees and all that, and how many
breakfasts do you have every springtime? And and it's exactly

(02:23):
like that. So so let's let's get into that. The
plants a feed themselves. That's what they do through photosynthesis,
as we all know, that's theme. But what they do
is they pick up all the elements that the soil has.
So yes, sometimes you need to put some NPK into
the soil, depending on what you're growing, of course, And

(02:45):
and basically what you're doing is you make sure that
there is enough of this stuff that the roots can
pick up. That's what it's about. That's the guts. So
there's three types of fertilizers that I could talk about.
You know, generally speaking, we talk about general fertilizer, which
is NPK and more or less the same sort of

(03:07):
matter of numbers NPK seven three, six or twelve, four thirteen, whatever,
But it's always to do with a nice balance. But
if you talk about n P and K, the n
is for making grass or green, you know, green material.
The PA is for the root zone and health of

(03:29):
the plant, and the K is for potash, which is
basically for your flowers and your fruit. So all these
three different things need a slightly different NPK ratio. I've
written it down on Libby's email thing. You can find

(03:49):
it in there. Potatoes has more K, so more in
the middle, tomatoes mirror at the end. It's a rose. Fertilizers,
all that sort of stuff, and this is how you
go on. But what I tend to do is I
go for general fertilizer. Quite often. I use seaweed or
sea footstoop some that when forgod stuff, but I use

(04:09):
it in a really light manner when I water the
plants in the tunnel house. And then what you do
is you add a little bit of pottash. If you
want fruit, you add a little bit of K. If
you want roots, and you a little bit of and
if you want green material. You know, yeah, that is

(04:29):
It's a very simple technique.

Speaker 2 (04:31):
It is.

Speaker 3 (04:32):
And ye that helps you out.

Speaker 1 (04:34):
Yeah that sounds.

Speaker 2 (04:35):
That sounds great. So I've been using a lot of
a lot of seaweed at home.

Speaker 3 (04:39):
Yeah, not a lot.

Speaker 2 (04:40):
You know, you've got to be pretty potent. That stuff,
but you.

Speaker 3 (04:43):
Know, absolutely it is.

Speaker 2 (04:45):
Don't go for the top, I know, but it's it
is tempting to. I still have that. I still a
kind of like a child, you know, I'm like more
and more, but yeah, yeah no, but I think it's
already made quite a big difference at our place. So
thank you very much for that, rude. We'll make sure
all of your tips are up on the news stories
you'd be website and you can access those very shortly.

Speaker 1 (05:04):
For more from Saturday Morning, Jack Tame, listen live to
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