The problem with your soil resisting hydration is not uncommon. It usually begins with the soil being watered incompletely and then drying more than it should. After that it can become hydrophobic and actually repel water! The ingredient in the soil that is causing that problem is peat. It is a great addition to potting soil because, under normal circ*mstances, it retains moisture well and decomposes slowly.
The best technique to force the soil to rehydrate is watering from the bottom. For a smaller plant, you can do that in the sink. For a tree, you can place the pot into a tub or bucket of tepid water and allow the water to be absorbed up through the drain hole. There will be so much air in the soil at first that the pot will float and you will have to hold it down. Once the air bubbles stop rising it means that water has saturated the soil and you can remove the pot. Let it drain into its run-off dish and then empty the run-off water.
Once your soil has been reconditioned, you should be able to follow the standard watering technique for your plant. Thoroughly hydrating should be easier going forward.
Courtesy of NYBG Plant Information Service
