One of the most common mistakes people make is not watering properly. It’s an easy mistake to make since you can water a plant quite heavily and should be able to assume it has been watered. Unfortunately some soils & potting mixes can become water repellent so you can water for a long time until water is actually running off the surface but it doesn’t actually penetrate the soil.
An easy way to find out if you have watered adequately is to scrape away the top layers of soil/potting mix and check how far the water has actually gone into it.
If it hasn’t gone very far Don suggested two options:
Buy a wetting agent – there are several available at nurseries, Bunnings and other stores that sell gardening products. Two of the most popular brands are Seasol Super Soil Wetter and Wettasoil. Work out from the directions how much of the product you’ll need and use a watering can to apply it. It could still take some weeks or even months to get the soil to re-wet but it’s worth persisting with this.
The other option is to use a watering probe. This is a very useful tool for watering plants. The end is poked into the ground and when the water is turned on it actually waters the area underground but even then it can still take weeks for the soil to wet evenly.
Wetting agents are available at nurseries, Bunnings and other stores that sell gardening products.