Saturday, January 22, 2011

How to grow Sarracenia to perfection - pots and soil

***Photos to come after the next repotting***

Summary - Healthy roots and rhizomes make a healthy plant. Make sure you give your Sarracenia an acid soil able to hold both water and oxygen, and also enough soil in the right type of container to promote oxygen exchange and room to grow for as long as possible.

Because we grow Sarracenia for their leaves and foliage, we tend to overlook or even forget the roots and rhizomes. Many people see them as boring, esoteric things that get a quick glance at repotting, and never again. The reality is that giving Sarracenia roots the conditions they need to grow well will give you a much healthier, hardy and beautiful looking plant. Because root care is probably the most complex topic I'll cover, I've split it into sections:
  • About Sarracenia roots and rhizomes...
  • Root health
  • Soil media
  • Container choice
  • Repotting
  • Rhizome health
About Sarracenia roots and rhizomes...

The difference between roots and rhizomes is something not often touched on in the CP literature. In short, a rhizome is a branch modified to grow on or through the soil. This branch, just like a conventional one above ground, has growth points or nodes from which foliage or roots grow. Which is produced depends on a complex set of interactions between plant hormones.
As for the roots themselves - their purpose is to anchor plants in the soil and to absorb water and minerals dissolved in the water. Sarracenia produce roots that branch multiple times, eventually dividing into very fine hair-like structures (appropriately named root hairs!) that do most of the roots' work. Unlike other carnivorous plants, Sarracenia have relatively large root systems that can cover a lot of soil. They also appear to be quite efficient at absorbing nutrients - plants treated with dilute osmocote as seedlings can be grown to flowering size in as little as 3 years, while unfertilised plants need 5 years or more! Messing with roots of long-lived plants like Sarracenia too often can stunt their growth and set them back many years, so it is important to treat them well from the onset. The root hairs in particular are very fragile and can take some time to regenerate, time in which the plant cannot access water efficiently and is therefore stressed.

Root health

To be truly happy, Sarracenia roots need to be kept in an acidic environment that is both wet and well oxygenated at the same time. To achieve these conditions, care needs to be taken in choosing appropriate soil media and pots - things that need to be considered in tandem for reasons outlined below. Provision of water is a separate condition that will be treated separately.

Soil media

Getting the soil media right for Sarracenia is half the battle as far as looking after their root systems is concerned. A good media is something that is acidic, holds water but is also well drained and allows good penetration and exchange of oxygen from the atmosphere. The media suggested by most CP books achieve these to varying degrees, but all have either of two things in common - they are based on either peat or Sphagnum moss.

Peat and Sphagnum are closely related - peat is merely the substance produced when live Sphagnum moss gets buried by new growth and rots in an oxygen poor environment. Sphagnum moss itself generates very acid conditions because it continually releases hydrogen ions into the environment while living. The hydrogen ions then turn the surrounding environment very acid. They are both great for use as growing media components because many Sarracenia naturally occur in Sphagnum-dominated habitats.
There are pros and cons to using both peat and Sphagnum. They are:

As you can see, Sphagnum has some great pros, but also some very prohibotive cons. It is somewhat fussy in its requirements, dieing easily if the humidity is low or the pot dries out briefly. Hard water also kills it when minerals in the water react with the acid and form a buildup on the moss' surface. This buildup eventually smothers the moss and kills it. Dead Sphagnum can also decay into a slimy mess that prevents oxygen reaching the roots and can promote pests like nematodes.

The problems with Sphagnum can be overcome if you are prepared to use shallow orchid or waterlilly basket pots with mesh sides, and keep the pots sitting permanantly in relatively deep water in cool, humid conditions. Unfortunately, these conditions can be hard to provide in some parts of Australia. But the true disadvantage of Sphagnum is that it makes it very hard to see pests such as scale insects and mealybugs (especially the latter, which can get into the Sphagnum itself!), and treating them chemically can kill the moss. Weeding is also nigh on impossible, especially if you get a herb that spreads via rhizomes or stolons. Fertilisers with high phosphorous ratios will also kill Sphagnum by smothering them in algal growth, although a low phosphoroust fertiliser will not affect Sphagnum noticeably. In short - if you can grow Sphagnum well, it is a great medium to use. But if you can't, it is generally wasteful to rely on it.

In comparison, peat moss is easier to deal with, mostly because it is a dead medium. It is cheaper than Sphagnum, but some of the lower cost is absorbed by the cost of sand and perlite needed to maximise soil aeration and root penetration properties. Peat used on its own can compact too much to allow adequate aeration and can also disrupt good root growth. It provides most of the properties of Sphagnum (water retention and acidity), but it does tend to leach acidity over time, especially if hard water is used to water the Sarracenia. In such a situation, you don't really have much of a choice but to repot as frequently as needed to keep the soil in good condition.

In making up a peat mix, you also need to consider the type and amount of sand and perlite needs to be mixed in. Sand should be as coarse as possible and not alkaline - test this by filling a glass with vinegar and sprinkling in a small amount of sand. Alkaline sand will produce bubbles for some minutes as it reacts with the vinegar, whereas inert sand will not fizz at all (but may release air bubbles trapped between grains). Perlite should also be as coarse as possible - it is simply inert volcanic ash that is superheated until it pops like popcorn. If you have hard water where you live, I'd suggest using more peat and sand than perlite to get as much acid from the peat as possible. If water hardness is no issue for you, then equal parts of peat, sand and perlite will give you a fluffy, acid mix that holds lots of water but is also aerated. Such a medium is perfect for promoting fine root growth, and will do much for creating a hardy, beautiful plant.

Container choice

Pot choice is something that has been touched on by only a few CP books (The Savage Garden being the best - forget everything Slack says about pots for Sarracenia in his Carnivorous Plants, his text in Carnivorous Plants and How to Grow Them is more reliable!). Despite this lack of attention, pot choice is something that will pre-determine how well your plants grow. The type of medium you use for your plants will also largely determine what type of pot you should use for your plants.

Pot type is the first consideration. If you use Sphagnum, I'd strongly recommend using waterlilly baskets or orchid pots with mesh sides. Because Sphagnum needs high water availability if it is to do well as a medium, choose squat pots - because the mesh sides allow air penetration, deeper water can be used without affecting root growth. Only the top layer of Sphagnum will grow if you use a conventional pot, making it more susceptible to being killed by low humidity or hard water.

If you use a peat medium, conventional solid-walled pots are perfectly fine. Unless you use solid-walled foam boxes as water trays, use a light coloured pot - foam boxes are great for water trays because they insulate the pots against the sun. Standard height pots are fine for pots up to about 200 mm (8") in diameter. Anything larger will need to be a half-height or squat type pot to keep an acceptable water table.

Pot size is also important. Adrian Slack's first book (Carnivorous Plants) suggested using a maximum pot size of 140 mm, advice that has somehow ingrained itself into many long-time growers. This is likely because, for many growers at least, 120-140 mm pots work well for the most part. For one, they don't let plants get so large that their rhizomes start to rot out. Second, for some strange reason, tightly potted plants seem to do very well, despite their large root systems.

Although Adrian later recommended much larger pots, this later advice never really stuck. The advantages of using a larger pot are more room for root and rhizome growth, more stable soil temperatures (small pots heat up fast), better water availability and better ozygen penetration to the root zone. Unfortunately, how big a pot you can safely use is not something I can tell you. It is something you need to find out for yourself under your own growing conditions. Start off with a 120 mm pot - 140 mm if it is a bigger plant - and see how big it grows before it needs to be divided. You can generally tell a plant needs to be repotted and divided when parts of the rhizome start to die off. Just make sure you don't let your plant rot out!

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