When to water potted plants
Some time ago a client phoned me, he was having trouble with a Casuarina bonsai. Almost all problems with potted plants are related to watering techniques so this was my first question to him “has it dried out ?”. His response was “my trees never dry out they’re always moist”. So therein lies the problem. Potted plants must dry out between watering. The roots of plants take in water and nutrient as we all know but they also breathe. When a plant is watered the air pockets in its potting mix fill with water, as it dries out the water is replaced with air. This cycle of wet then dry is required for the roots to perform both functions.
I am always interested to read the instructions on plant labels, re watering they mostly advise to water when the surface dries out. I have an issue with this theory because the surface of course dries out first and a dry surface is no indication of whats happening in the rest of the pot. The very best way to test if a pot is dry is by weight. It doesn’t take long to teach yourself to gauge moisture levels by simply picking up the pot. For large containers you will need to use touch but be sure to dig your fingers well down into the pot, this is not ideal. I never pot plants directly into decorative pots but rather use inserts for this very reason.
The quality of potting mix can have a big influence on watering. A potting mixes particle size is so important, fines are the enemy, good quality potting mix should have minimum fine particles. With time fine particles will move down to the base of the pot where they often form a sludge and inhibit drainage. Its important for the plants roots to colonise the whole pot and a layer of wet potting mix at the pots base will prevent root development at that point.
Pot size is another important factor re watering. Its often thought that potting a plant in a very big container will speed up it’s development, this can be the case with very fast growing plants but in general its better to increase the pot size slowly, just one size up each time.The quicker the pot fills with roots the easier it is to control watering as a pot filled with roots will dry out evenly. Conversely a large pot with lots of empty space is difficult to water and more importantly difficult to dry out.
How often do I water my pot plants ?.
This is a question I get asked relentlessly and one thats impossible for me to answer. The correct response is “when it’s dry” but that comes across as a little condescending. There are so many variables it is impossible to give a short answer. Where is the plant situated ?, what climate/microclimate do you live in ?, is the plant exposed to sun/wind/rain ?. Watering is going to vary from season to season and generally it is better to keep plants a little dry during dormancy. So if you are growing indoor plants they are mostly tropical therefore over the winter months they prefer to be dry. For tropical plants dry and cold can be tolerated but wet and cold is almost certain death. On the other hand if you are growing spring flowering bulbs then the summer is when they like to be dry and watering commences in Autumn and ceases once the foliage begins to deteriorate. Evergreen plants such as Azalea or buxus will require less water in the cold weather but Australian natives are often opportunistic growers meaning they grow when the conditions are right so as potted plants they can grow all year round. So many variables. Learn to read the plants you grow, generally their appearance will tell you their requirements. Health issues almost always show up on the new growth so at the tips. All plants shed old foliage, the old leaves will yellow then drop. It is only when this happens to new growth that you need to be concerned about.
Of late I have noticed that plants produced by big production nurseries are potted in pure coco peat. This potting medium may be good for large scale production but I find from the home gardeners point of view its very difficult to control moisture levels. My advice would be to pot your new plants into a regular pine bark based mix as soon as possible.