You mention 'Heavy Clay' as the soil type. Maybe you would be better digging in planty of Garden Compost and in the Autumn a dressing of lime to help break up the clay. Clay in its self is fertile but just in the wrong form for plants to access it efficiently. Plenty of organic matter will do the job and build up good water retention like a sponge so watering systems shouldnt be necessary. Might take two or three years but you will bet the desired result.