Archive | 2 October 2013

Propagating Cane Begonias

Betty Vander Poorten (10)
Doing it my way!

I take tip cutting about 12-13cm (5in.) in length. Always go to a node which has not flowered. This hopefully will give you a nicely shaped plant. If you cut at a node which has flowered, the plant will not branch.

My propagating mix for canes is potting mix 80%, perlite 20%. I have also used straight vermiculite with great success. I always use striking powder, a habit from nursery days in Victoria because I believe it to be beneficial. Lots of growers do not use this powder.

August for me is the best time to do cuttings, but I have had success in autumn before the cold weather sets in. On an east facing wall I have large terracotta pots filled with lovely canes which get sun till midday in summer – the more sun, the better the flowering.

In August I cut back to four nodes in the centre of the plant and three around the edge. This gives a lovely flowering plant by the end of November/December. Fertilise with Osmocote Plus. If things are working your way …. Don’t change!


Pot Sizes

Angelwing Begonia in a pot

A potted angel wing begonia (Begonia aconitifolia × B. coccinea).

We have always been told that begonias like to have their root system fairly contained and it is disastrous to ‘overpot’ them. Most of the experienced growers who have written books or articles on begonia culture have stressed this point. I have often recommended using a smaller pot for growing a begonia in than one would see for an ordinary pot plant. Why? Because everyone says so and it has always been the rule. This is understandable in cool and or wet climates, or in glass houses which have a controlled atmosphere. Under such conditions the transpiration from the leaves and evaporation from the soil is greatly reduced.

The potting mix will hold its moisture for a longer period, and unless there is a large root system in relation to amount of soil, the water contained in the soil will become stagnant and the soil “sour”. I have found that it is important to pot newly rooted cuttings and small seedlings into very small pots because they usually have limited root systems and require oxygen (air pockets) to grow. It would be unwise to repot a begonia into a large pot at the beginning of winter when the growth rate is going to slow down and the plant will require very little moisture.

Excepting the previously mentioned conditions, I believe that in our hot, dry summers we can use larger pots than those we have been using. At the beginning of last spring my rexes in 12cm pots needed repotting. I know if they were put into 15cm pots that they would soon need larger ones and didn’t relish the thought of doing the job twice, so I rashly potted them into 20cm squat pots. I could hardly believe how rapidly they grew and they are still growing and looking lovely.

Over the years, I have always allowed seedlings and cuttings to grow quite large in 6cm pots before placing them in 12cm pots. Last season quite a few were potted on which I didn’t think were really large enough. The same results occurred – before I knew it they had to go into larger pots. Naturally if plants are going to grow larger and faster they will require more nourishment and I know that I do fertilise my plants more than the experts recommend. It has often puzzled me why they advise using liquid fertiliser at ½ to ¼ or even 1/8 strength. Even on tiny seedlings I use Phostrogen at full strength and they GROW.

Maybe compared to the USA we can use larger pots because of evaporation and stronger fertiliser because of more frequent watering and more rapid plant growth. Another contradiction I have discovered is in the depth of containers.

I had some pots delivered and it wasn’t until the carton was opened that I discovered that they were deep 12cm pots – not squat. They were used and the plants did well, soon sending their roots out through the bottom drainage holes. The roots of our plants may develop more quickly because they have to forage when our mix becomes drier between waterings. I was amazed to receive a letter from a grower who was lamenting the fact that she had pruned her canes right back at the beginning of LAST season and needed to have them looking good for a special event at the end of NEXT season. I always severely prune my canes in early spring and they are usually lovely by autumn. Sometimes they need to be trimmed in between. It must indicate that our plants do grow more rapidly.

Please do not start putting all your plants into huge containers. I would suggest that you experiment with a couple of plants that can be easily replaced.


Understanding Mildews

Powdery mildew, species Podosphaera fusca

Powdery mildew, species Podosphaera fusca

Fungus and mildews are always a problem during humid weather. Understanding how they grow can help when you are trying to control them. Fungi are often visible to the naked eye and are often named for their appearance.Powdery mildew is a group of related fungi, usually showing as whitish spots on leaves or new shoots. They live on the surface and send hollow tubes into the plant to suck out nutrients. Some powdery mildews attack a range of plants – some only attack one plant, or at the most, two or three. Powdery mildew is worse in humid weather, and once it has got a hold, it will keep growing, even in dry weather.

Downy mildew is also a group of related fungi, also worse in humid weather. The infected patches appear first UNDER the leaves. Downy mildew grows within a plant and sends out branches through the victim’s stomata (the microscopic openings in the leaves) to create pale patches on the leaves. The problem usually disappears in dry weather, or sometimes if you improve air circulation or stop overhead watering.

Spacing plants to allow good air circulation will help to control some fungal diseases. Environmental problems such as heavy rain, very hot sunshine, strong winds and consistently high night temperatures can also lead to the development of these diseases. The soil should be kept rich in soil organisms to provide conditions that are favourable for the vigorous growth of beneficial fungi and bacteria that will feed on other more destructive types.