Clay soil is classified as a heavy soil and one of the most difficult garden soils. Due to its compact nature, clay is slow to absorb water and absorbs the least amount of water of all six soil types. It's hard when dry, sticky when wet, drains poorly and warms slowly in the spring. It holds the most nutrients of any soil, due to the poor drainage. Some plants thrive in clay soil, while others can thrive with generous amending.