Cymbidium Culture

by Noe Smith

Getting your culture right is never easy, especially if you are relatively new to this Cymbidium growing game. Who and what do you believe from all the varied culture tips, views and opinions out there? The fact that every experienced and successful grower seems to do things completely differently from each other doesn’t help the new grower.

What often confuses beginners is that "experts" often only give part of the story when it comes to describing their cultures. This is not a deliberate attempt to confuse, just that they have been growing Cymbidiums for so long they tend to gloss over or omit the basics and concentrate on their results from a new fertiliser, potting mix, or similar. This tends to make newer growers think that all they need to do is copy so-and-so's fertilising or use their potting mix, to achieve the same results; of course, this is seldom the case. The truth is that successful Cymbidium culture relies on getting a combination of cultural factors right; miracle fertilisers, secret potting mixes, or any single factor won't give you success if one or more critical factors have been overlooked.

So what are the basic and critical factors which are required to grow Cymbidiums well? Just like any other plant, Cymbidiums require light, air, water and food to grow; get the basic combination right and you will be well on your way. Once you get the basics sorted, then you can fine-tune various aspects to improve (hopefully) the results you are getting.

Now Cymbidiums are pretty tough (as are most orchids despite what we have been led to believe); they generally won't die on you unless you get things seriously wrong, so let's look at the basics, one thing at a time.

A question worth asking before we start is what does a healthy Cymbidium look like? It is often the case that looking at your plants will give you some important clues as to what, if anything, might be wrong with your culture. A healthy Cymbidium should have mid-green coloured foliage, not dark green, or yellowish; the leaves should be more-or-less erect, not floppy; and the plant's bulbs should be plump and smooth, not wrinkled or shrivelled. The leaves should not have brown/black tips (if you live in South Australia this may be a common sight and is very hard to avoid due to the water quality supplied in that state), or brownish/bleached-looking areas where they curve out. There will be a little variation, particularly where the parentage of some plants includes Cymbidiums which naturally have long, wide, floppy leaves, or those that are naturally more light-sensitive or prone to leaf markings, but in general, if most of your plants look a certain way, the odd one out may just look different due to it's genetic make up.

The part of a Cymbidium we can't see (without knocking the plant out from its pot) is the root system. A poor root system can be the cause of a range of problems and can contribute to poor plant growth. Root systems usually end up in poor condition due to a number of factors: too little water, too much water, poor or broken-down potting mix leading to poor drainage, excessive fertilising, or incorrect pH (the ideal pH level for most Cymbidiums is around 5.5 if you want to check). A process of elimination should help in identifying which issues may be causing any problems you have and hopefully by the end of this article we will have covered all of the cultural factors necessary to help you adjust your culture if needed.

Light

Too often we concentrate on subjects such as fertilisers (which we will look at later) but ignore the issue of providing our Cymbidiums with the correct amount of light. Without adequate light, plant growth can be restricted and your plants may not flower, or will only flower poorly. Too much light can lead to sun damage to the leaves, which can in extreme cases leads to large areas of leaf tissue dying. Generally around 50% shade is considered ideal for Cymbidiums, though in some areas where summers are long, sunny and very hot, 70% or even 80% shade may be required.

Another aspect is the duration over which your plants are receiving light. Plants which are in heavy shade for a significant part of the day will not do as well as those which receive filtered light for the majority of the time the sun is up. Daylight hours of exposure are important and growing your Cymbidiums where they receive hours of heavy shade from buildings, or dense tree cover, should be avoided if possible. If you face these problems try to reposition your plants to minimise the effect of neighbouring buildings, etc. Remember, if your plants have leaves of a nice mid-green colour without any of the problems mentioned earlier, you are doing alright in the terms of light level.

Another possible problem which can reduce light exposure for your plants is overcrowding, leading to your plants shading each other. Ideally Cymbidiums should be grown far enough apart so that their leaves are not touching, but in the real world virtually no one achieves that! Remember, the more tightly you squeeze your plants, the less successful your flowering may be and of course cramming plants closely together can lead to other problems, such as disease transmission and lack of air circulation, which brings us to our next subject.

Air Movement

While we can't see it, air is no less important for good culture. Air, or more precisely, air movement and exchange, are as critical to good plant growth as any other factor we will look at. Cymbidiums grown under shade cloth will receive whatever air movement nature provides and in nearly all cases that will be adequate, but plants grown in houses or enclosures covered with a solid material can suffer from lack of air movement and exchange. Just like us, plants breathe and require that the air in their growing area be regularly changed.

If you grow Cymbidiums in an enclosed hard cover house, ensure that adequate ventilation is provided. If necessary, install some sort of fan which stirs the air or draws fresh air into the house, though fans should not be aimed directly at the plants. The plants closest to the fans could become dried out if the full force of a fan is continually blowing on them.

Stagnant air can lead to poor air quality, which in severe cases can be detrimental to plant growth and will certainly increase the risk of fungal infections and insect infestations. Even when plants are under shade cloth, air movement can be seriously restricted if your growing area is sited close to high walls or buildings or between similar obstructions.

Watering

Watering our plants can be a difficult thing to get right; just what is too much or too little when it comes to watering? Unfortunately there is no easy answer. Where you live combined with all the other factors related to plant growth will play a part, but there are some guidelines and some simple observations which will help in getting it right. If you live in a hot area with a climate with naturally low humidity, or an area prone to strong and regular winds, then your plants may well need watering more often than plants grown in an area where those factors aren't as extreme. We used to live and grow Cymbidiums in an area where all of those conditions applied and we needed to water more frequently than we do now living in coastal Victoria.

As a general rule, watering every couple of days in summer, every four days in spring and autumn and once a week in winter will give you a reliable starting point. Make sure you water well at each watering – until water runs out of the drainage holes in your pots – this not only ensures that your potting mix is wet right through, but also draws air into the root system which is necessary for good Cymbidium growth.

The Cymbidium species which are in the background of the majority of our modern hybrids are semi-terrestrial in the main; in the wild they grow in leaf litter, rotting plant matter, etc., often built up in rock crevices, between tree roots and similar places. They do not grow in the ground in soil.

How often you need to water will be influenced by factors such as temperature, time of the year, size of plant in relation to the pot it is in and potting mix/media. Plant growth slows in winter, humidity is usually higher and temperatures are lower; therefore your plants will require less frequent watering. A plant which is in active growth and has filled its pot will need watering again before a plant in a bigger pot which it hasn't filled, as there will be more mix to hold water around the roots in that pot. It's a matter of learning how quickly your plants dry out. Look at them and if you like, test their weight. How heavy does a particular plant feel just after you've watered it? How heavy does it feel a couple of days later? Look at the potting mix; it will probably be dry on the surface a day or two after watering, but is the mix visible through the drain holes still wet?

Ideally Cymbidiums should be kept moist and never allowed to dry out completely. Many potting mixes such as pine bark can be very difficult to re-wet once they become dry. If you water your plants and the water rushes straight out of the pots drain holes, it is a fair indication that the mix has dried out. If you need to re-wet a plant, placing it in a bucket and filling the bucket with water almost to the top of the pot will work. Leaving the plant in the bucket of water for an hour or two should do the trick.

While it is important to keep Cymbidiums moist, avoid over watering – moist means moist, not sodden. A mix kept overly wet for an extended period will almost certainly lead to a break down of the plant's root system. Like any other plant, Cymbidiums can't grow without roots. While Cymbidiums will grow new roots if the problem is rectified, the plant will be retarded for a season or two. Overly wet potting mix and loss of the plants roots can lead to the eventual loss of the plant due to various rots spreading through the plant's bulbs.

Fertilisers

Now we come to possibly the most misunderstood area of Cymbidium growing and certainly the one that can be most confusing to a newer grower – fertilisers. Cymbidiums need a certain range of nutrients and minerals to grow well, just like any other plant, animal, or human. Most commercial fertilisers will provide the basics needed for adequate Cymbidium growth, leaving aside specialist mixtures designed for particular plants (eg. Australian native plants). Any of the commercial balanced fertilisers commonly available at garden centres, hardware stores and supermarkets will provide everything a Cymbidium needs in most situations.

How much fertiliser you give your plants is just as important as what type you use. Cymbidiums are not gross feeders like quick-growing bedding plants or vegetables; they don't need to be fertilised at the rates you would use for tomatoes. Unlike your veggie patch, where "if a little fertiliser is good, more is better" DOES NOT apply to Cymbidiums. In fact, it is advisable to halve the recommended rates given on commercial fertilisers when using them on Cymbidiums. As a starting point, there's an old saying: "fertilise weakly, weekly" and it is pretty good advice.

Some growers prefer to vary the fertilisers they use rather than sticking to just one brand and formula. The logic behind this method is that slightly different formulas may better cover the needs of the plants. Some growers like to alternate between mineral-based fertilisers and organic-based ones (such as fertilisers based on fish, sea weed, chook poo, or combination of these types).

Some growers opt for slow-release fertilisers in pellet form; these fertilisers have the advantage of supplying a little fertiliser each time you water your plants and provide a good safety net if used at the correct rate. If you fancy this type, go for a nine-month slow-release applied in early spring to keep up the supply of food through the peak growing period. Application for this type would be about a heaped table spoon applied to a 200 to 250mm pot with the amount varied either up or down for larger or smaller pots. Stir the pellets into the top couple of centimetres of the mix when you apply it, as this seems to give a more reliable and consistent release of nutrients.

Sooner or later you will hear someone talk in glowing terms about some almost magical fertiliser, whether commercially made or some special brew. Change to any of these types if you wish, but remember to find out what other cultural practices the person advocating it uses. Did they have to change some aspect of their culture to accommodate their special fertiliser? What rate do they apply it at? Always remember that no fertiliser by itself will magically solve your growing problems or turn you into a top grower overnight. If you aren't sure about making a wholesale change, select a few plants and test the new fertiliser on them just to see if it gives results which are better than what you are currently getting.

You will have noticed that no mention has been made about N.P.K. ratios or trace elements. For those who don't know, N.P.K. stands for nitrogen, phosphorous and potassium, some main components of most fertilisers. Some growers prefer to use a fertiliser high in nitrogen while plants are in active growth and one high in potassium when flowers are developing. Others believe that using those two types the other way around is preferable. You can do either, or use a more balanced type and probably achieve about the same results, IF you use them at the right rates. If you want to research the effects of various N.P.K. rates you will find plenty of information is available, but a good starting point will always be a good quality balanced mix. One word of caution – high nitrogen fertilisers can be too much of a good thing, as they will encourage rapid growth but can also cause soft growth both of foliage and flower stems and even retard flower development. Personally I prefer shorter but tougher leaves and more flowers on strong stems. A good all round N.P.K. rate would be around 15-10-10 (one we have used for several years is 15-13-12, which we alternate with an organic type at 8-2-5).

Potting

When we began growing orchids, the common Cymbidium mix was known as UC mix (developed by the University of California). It consisted basically of peat moss, rice hulls, isolite and a small amount of pine bark. Composted pine bark was unavailable at that time and people composted their own – a long, boring and messy process. As composted and graded bark became available, more Cymbidium growers changed to it, either on its own or combined with other materials. Pine bark had the advantages of being reasonably consistent, easy to use, free-draining, relatively long-lasting and commonly available. It is still a good medium for potting Cymbidiums, but make sure it is composted – raw pine bark contains a lot of tannin and will kill root tips if not treated. The process of treating bark requires soaking it to remove the tannin (usually with the addition of lime) or weathering it in piles for lengthy periods.

In recent years, coco fibre has become a popular medium, either on its own or combined with bark, perlite, or both. We currently use a mix of 60% coco fibre in chip form with 30% composted pine bark and 10% canunda shell. This mix seems to combine the greater water holding quality and long life of coco fibre with the good drainage of bark at a level which suits our culture and local climate.

Those last few words are the important part – a potting medium is only one part of an overall culture program. The same mix in a more humid environment may remain too wet; if we watered more heavily or more often, it may not work as well as it does. Whatever medium you choose, make sure you watch how it behaves and, if necessary, adjust your watering to suit. Most potting mediums offer little, if anything, in the way of nutrients; they are primarily intended to hold the plant firmly in the pot and retain sufficient moisture and nutrients from fertiliser to assist plant growth, while providing air space within the mix and adequate drainage.

Remember: Light, Air, Water, Fertiliser and Potting Medium – they all work together.

Noe Smith