Bihrmann's   CAUDICIFORMS   

 Water   Watering   Nutrition  pH   Light   Ventilation  Temp.   Soil   Pots   Pruning   Rest

Besides from the already mentioned factors, there are a few more, more or less odd ones.
While we spoil out plants, we also create a good habitat for other organisms. Fungi and bacteria does not always keep to the dead tissue. In general, a healthy plant is able to fight them back, but not always.
There are a lot of chemicals, but also a line of other, less hazard ways to fight them back.

Fungi & bacteria thrive if the humidity is high. Some not so harmful-to-human chemicals like sulphur can fight them back.

Pests appreciate our misunderstood efforts to grow food for them. And they can really thrive in the paradise, we make for them: Plenty of food and no enemies.
Some like lies and spider-midgets are a real menace, and can be hard to get rite of. Chemicals solve it, but other ways work as well.
I've been using predator insects, nematodes and bacteria with huge success. A simple spray with cold water ruins the day for lies. A common homemade poison, made from tobacco, alcohol and soap, mixed in water works fine as well. But be careful: the nicotine is dangerous!

Others animals are, at least in the wild, a great help to the plants. Earthworms, bacteria and fungi make compost, while bees birds and mammals fertilizes, ants bring home nutrition and defend the ant-plants, insects feed the carnivorous plants and so on.

Age is just, like for another organisms, a deadly, sexual transmitted disease. You can fight it back with renewing your plants from seeds or cuttings.

Gravity! It may sound odd, but it is a factor, when you make cuttings of some species of plants. Some have to lie down to root.
We like our plants to stand straight, but they control their direction by light, not gravity.  

Love! Some people are just better at growing plants, than others. I have heard that talking to your plants make them thrive. I think it get down to "timely care". It is about having the time to observe your plants, water them often, pay attention to pests, dull leaves and so on.
No doubt: The plant collections that I have been taking care off, around the world, have thrived the most, when I got plenty of time to care for them.

Other factors, that still haven't been scientific discovered/documented might play a role as well, But I leave that to others to explain.

 Water   Watering  Nutrition   pH   Light   Ventilation  Temp.   Soil   Pots   Pruning   Rest