Tuesday, November 6, 2012

The pros and cons of fertilising Sarracenia–and what happens if you overfertilise them

You don’t have to fertilise to get lovely Sarracenia! This is a Sarracenia flava var. cuprea ex Gotcha! Plants. Fortunately, it survived the fertiliser carnage described later on this page.

Prologue - If you are an experienced CP grower and read only one article on my blog, it should be this one. I wrote it in response to questions people had asked me about fertiliser use in late 2012. By mid summer, I had lost significant numbers of plants to what I thought was a weird fungal rot. I later learned it was fertiliser burn.

Fertilising Sarracenia is a relatively new thing. It was not usually mentioned in the original texts on CPs (although I think Schwartz in his 1970s book did suggest it from memory), and even today opinions vary widely on how to fertilise and what the benefits are.

I have successfully (and unsuccessfully) used fertilisers on Sarracenia. It comes at a price that may or may not be acceptable depending on why you grow plants in the first place, and on your growing conditions. If you get the dosage wrong, you will loose plants – period.

A word up front – these are just my personal, anecdotal experiences. I have not conducted a rigorous, controlled study into fertilisation or considered variables like application and nutrition rates (although I would like to). But I have tried fertilisers over a few years now and have some experiences to share.

Types of fertilisers suitable for use on Sarracenia

Fertilisers suitable for use on Sarracenia fit into two groups – slow-release pellets and liquids. I have mainly used slow release pellets, having used liquids for just a few months at the end of a growing season at half the recommended rate. I would like more experience before I develop a firm position on them, although I did not notice any problems, including when I accidentally used one at double the recommended rate. They are, however, more work compared with slow release pellets, as they need to be mixed and manually sprayed unless you have a sophisticated irrigation setup.

Slow release pellets look like miniature peas and can be mixed into potting mixes or simply scattered over the tops of pots. I have always just scattered them onto the surface of my pots, but avoid dropping them onto sundews or into pitchers (Drosera leaves catching the pellets invariably shrivel up and die within days).

The rules for applying fertiliser – this information cost many Sarracenia their lives, so read it well.

If you follow these rules, you should be ok if you have healthy, robust plants – always experiment first to make sure they apply to your situation. If you break or abuse these rules, I guarantee that you will have dead plants in a year or two. Use no more than 4 pellets of fertiliser per 100 mm/4” full length pot. If you apply more, you will eventually loose your plants – if not this year, then certainly a year or so later. It just depends on how healthy they were to begin with, as it determines how long they can hold up. Don’t believe me, or think I’m misdirecting you away from my secret? See how many pellets I was putting into my plants in the photos below. Many of these plants died due to fertiliser burn, and it took two Plant Pathologist colleagues several years to arrive at that conclusion – the symptoms of fertiliser burn and the aftermath look superficially similar to a cryptic fungal infection.

Also, apply fertilisers only when plants have broken dormancy in spring – do not apply later in the season. Fertilisers can harm non-growing plants, so applying slow-release too late may cause problems at the last of the fertiliser leaches from the pellet after plants go dormant. Some slow-release formulations can last for 6 months, so be careful.

N:P:K ratios

The N:P:K ratio describes the amount of Nitrogen, Phosphorous and Potassium the fertiliser contains, in relative quantities. General-use fertilisers often have 7:7:7 ratios. More specialist formulations are available, and I always use a formulation for acid-loving plants (CPs in general grow in acid, nutrient-limiting soils). These fertilisers typically have reduced amounts of Phosphorous. For example, the current fertiliser I use (Scott’s Osmocote Slow Release for Australian Native Plants) has an N:P:K ratio of 17.9 : 0.8 : 7.3. Why use fertilisers with low phosphorous? Have a look at this graph:


As you can see, phosphorous is not always available to plants in high amounts. At low soil pH (< 3), very little is available. Between pH 3-4, there is a relatively high amount available, before it remains at medium levels. At pH 6, the amount again increases, reaching a maximum around pH neutral (7). If you put too much phosphorous into soils with pH 3-4 (about the pH of Sphagnum), then there can be an oversupply in the soil. Here is what happens if you oversupply phosphorous to acidic soils (note insane number of pellets – you have been warned!):


Yuck! Algal growth! The excess phosphorous is used by algae to grow, smothering out the live Sphagnum. Even if the Sphagnum is dead, algae will still grow all over it, just as it will grow over peat moss:


Although I overdid it here with the amount of fertiliser, algal growth seems to occur whenever people fertilise their Sarracenia even at acceptable rates. Every grower I know who use fertilisers ends up with algae growing on their pots. At the time when I thought I could get away with this level of fertilisation, I regularly flushed out the water trays to remove liberated phosphates. But when I realised something had gone very wrong here, I ended up hand picking out the fertiliser pellets in these very pots. By then, I was loosing plants.

Ironically, Juniper, Robbins and Joel in The Carnivorous Plants (1989) note that Sarracenia are both Nitrogen and Phosphorous limited by the conditions of their natural habitat, and that this is a reason why they catch insects. While the use of a Nitrogen- and Phosphorous-heavy fertiliser for carnivorous plants seems to make sense for this reason, it is obvious that an excess of Phosphorous can be a bad thing too.

Why did I use so much fertiliser – what was I thinking? Well, a certain, world-respected CP grower gave a talk at a certain Carnivorous Plant society meeting in Australia in Spring 2012 and just happened to claim that Sarracenia can take large amounts of fertiliser. As I has got away with 12+ pellets per pot the year before, I thought I’d double it based on what said grower had claimed. As did another member of the same society. The result - carnage.

Moral of the story – do not be tempted to overdo it with fertilisers, even if it is someone who is respected in the CP community.

See also this post for how to recognise and treat fertiliser burn – the symptoms are similar to fungal rots.

Acceptable use - fertilisers to increase pitcher size and seedling growth rates

Fertilisers do boost seedlings along. I have seen a grower in Australia use a 7:7:7 fertiliser with great success in this regard, growing all his plants from seedling to sale-ready plants in about 3 years. I have seen similar results with some seedling S. flava in my own collection as well with the native plant fertiliser. I will definitely use fertilisers to boost seedlings along in future.

I am not so convinced that fertilisers increase pitcher size in established plants when insects are available. My motivation for using fertiliser in the first place was because insects (especially flies) do not appear in large numbers until rain has fallen after the last frosts (this occurs around early to mid November). In contrast, plants in the greenhouse were up and growing by September. I thought using fertiliser would keep growth going until the flies appear, but now all my plants are outside, it is a moot point. I suspect that fertilising plants getting enough nutrients from insects may also cause problems – experiment needed here!

Affect of fertilisers on pitcher colour

Fertilisers do tend to wash reds from pitchers, especially the red forms of S. flava. The loss of pigment production is temporary, and I have usually seen a recovery begin by mid to late summer – the plants never get the same amount of pigment as they would otherwise have developed. If you are wanting to boost seedlings along to a reasonable size, it may not matter so much if the colour is not fully developed, but it may be a problem if you are wanting to select for more colourful clones (especially when space is limited). At the time this was written (late 2012), my plants were in a greenhouse whose cover was getting and old and blocking light, so I don’t have any plants to make a valid comparison between (the extra sunlight may also have increased their colouration).

Pros and cons of fertiliser use

So to conclude, here are my observations of the pros and cons of using fertilisers:

Fertiliser Pros Fertiliser cons
  • Can accelerate seedling growth by several years
  • May supplement nutrition for plants when few insects are available
  • Temporarily reduces red pigment production in pitchers
  • Causes algal growth on growth media surfaces at low pH
  • Kills live Sphagnum moss
  • Can and will kill your Sarracenia if you add too much.

So, are fertilisers for you? Hopefully, this page will help you make an informed choice, and if you do decide to use them, do so wisely.

Epilogue: the S. minor and S. flava var. cuprea at left died from fertiliser overdose, as did the S. leucophylla “Tarnok” at right. I also lost significant numbers of S. alata, S.flava var. atropurpurea and assorted other plants.