Gardening is a great workout because it uses all the muscle groups in the musculoskeletal system, but all the squatting, crouching and bending over can be tough on your back. Here are six tips to ease the strain. Change your position The most important thing when gardening is a change of position every 20 minutes, says Andreas Sperber, a physiotherapist with Germany’s Healthy Back Campaign (AGR). “If you have been bending forward, stretch backwards to counteract shortened muscles.” Watch your posture Bending forwards while gardening can be particularly harmful to your back. Consider setting up…