Well, I'm late jumping in here but I don't see where the following was mentioned, so here goes> Don't dig under the concrete foundation of the a/c unit. The unit may settle lower there and throw the fan blade off balance, creating bigger problems and expensive service calls. However, if you have other stuff growing within a foot to 18" of the unit, you should try to transplant them or cut them back if they cannot be transplanted because the roots are too close to the foundation or something. The a/c unit needs to have good air circulation to properly function. Also, if you have cottonwood trees or other plants in the neighbourhood that produce downy seeds (milkweed), you'll need to clear those away from the sides, gently, as those radiator fins are delicate and bend easily.
Not exactly on topic but relevant, nonetheless. Getting off soapbox now.