Proteas and Phosphate; a plant rant.

That’s it! I have had enough!! This has gone on for far too long!!!

I can’t cope any longer with seeing dead and dying members of the Proteaceae in garden centres. There is no need for these plants to be in this state.

‘What on earth are you talking about?’ I hear you ask.

Well, the answer is simple. There is a huge problem in British garden centres with the way plants such as Grevillea, Lomatia, Banksias and Proteas are looked after and it could be changed very easily.

Really strong, otherwise heathy plants are bought in from wholesalers, to be sold on by the garden centres and DIY stores, with every good intention of being able to sell something a little unusual. The plants last long enough in the garden centre to be sold to an unsuspecting customer who then plants them, proud of their purchase, only to find that weeks or months later their plant DIES.

What’s going on?

When the plants arrive at the garden centre in their liner pots the, unknowing, horticultural staff treat them the same as all the other plants. They pot them up or top dress them with a mix of whatever the preferred compost is and add a good helping of their proprietary granulated, slow release fertiliser.

Here lies the problem. Proteaceae, you see, are ‘allergic’ to Phosphates.

The wonder ‘slow release’ fertiliser is, more often than not, a thing called ‘Osmocote Exact – Standard 12-14 Months’ it contains a long lasting supply of all the ‘essential trace elements’ required (although I tend to disagree) for good plant growth. With an N-P-K (Nitrogen-Phosphate-Potassium) value of 15-9-11 (15% Nitrate – 9% Phosphate – 11% Potassium) essentially what the well-meaning horticulturists are doing is giving the poor plant a good helping of poison.

Proteaceae have evolved over their 100 million years on this planet to cope very well with the nutrient leached, old and often acidic soils of the Southern Hemisphere. These soils are low in N-P-K (some South American soils are high in Phosphate but its locked away from them by a chemical process caused by the soil being acid) and high in other minerals and the plants have adapted as such.

Their hard leaves have a high percentage of Lignin so that they don’t wilt and can grow even with the lack of sufficient Phosphorous for good cell growth. They have annual root systems, called Proteoid roots, that sit just under the surface of the leaf litter layer accessing the scant nutrients during the short periods of wet (and subsequent leaf litter breakdown) and they don’t have Mycorrhizal (fungi) relationships providing their mineral nutrients in a format that is easy for them to use. Many Fynbos/Mallee/Sclerophyll plants can fix atmospheric Nitrogen and out of them all the Proteaceae are the most uniquely and inextricably adapted to their environments.

In short they don’t need or want N-P-K.

Phosphate necrosis in Lomatia ferruginea

Phosphate necrosis in Lomatia ferruginea

A happy and very healthy Lomatia ferruginea

A happy and very healthy Lomatia ferruginea

So what happens to them?

The first sign that they are getting too much Phosphate is that they start to get a greyish/redish hue to their leaves. The leaves and flower buds eventually turn black and start to fall off. Sometimes the plant puts up last ditch fight for life, sprouting from the base, desperately clinging on. This is however to no avail. Other symptoms include a lack of growth, leaf tip necrosis, inter veinal chlorosis and eventually succumbing to Phytopthera. What a horrific end for a plant.

It’s not as simple as just the Phosphate either. High levels of Nitrate (15% is too high) fed to the plant to quickly in the presence of the Phosphate exasperates the problem. High levels of Calcium in the compost (most potting composts contain quite a lot of it which makes them alkaline; which, in turn, makes the Phosphate even more accessible to them) can also lead to Phosphate toxicity.

Why doesn’t it happen as soon as the plant receives the fertiliser?

Proteaceae have got a bit clever in their millions of years of evolution. They go through dormant and active growth phases. They grow when the going is good and remain dormant when life is tough. When in active growth they put on massive amounts of special annual roots called Proteoid or cluster roots. These roots are specially adapted to extract as much nutrition from the poor soils and leaf litter they are growing in as possible. It’s generally not until they start to put out these annual roots, sometimes months after they have been bought and planted, that they start to suck up all those noxious Phosphates, show symptoms and die.

Now it’s kind of alright for someone like me that would buy a plant and remove any fertiliser top dress from the pot before planting the plant. However, someone buying a Grevillea for the first time and suffering this problem would be put off growing a Grevillea ever again.

I just don’t think it’s fair that hardy, easy plants like Lomatia ferruginea, Grevillea rosmarinifolia and Embothrium coccineum should be dubbed difficult or even ungrowable just because of a mistake on the part of a garden centre staff member that is not paid enough to THINK. It’s not just Proteaceae that have this problem either. Some Acacias, Callistemon and Boronias suffer too. In fact it’s one of the reasons that Australasian plants are deemed difficult in British cultivation.

I have seen so many garden centres selling plants doomed to Phosphate necrosis, even one plant centre in a well renowned botanic garden had Grevillea plants suffering this problem. All it would take is a little information, a warning label on the plant saying something like ‘DON’T FEED ME!’ or a factsheet produced by someone like the HTA wouldn’t go amiss. For now though I think it wouldn’t hurt if everyone that knows about this problem could just tell their local garden centre staff about it and that way, just maybe, a few fewer plants will die needlessly.

Rant over!

Ps. Phosphate is also no good for many trees, native grassland plants and bulbs.

Pps. The mining of Phosphate causes massive environmental damage. Check out what happened to the island of Nauru.