Garlic seeds or bulbletts can be sown in pots to get them going and then you can plant them out later. Also when planting them in pots use a soil based potting compost such as John Iness seed compost. This is available from most garden centres. Using this type of compost tend to help when it come to transplanting as it tends not to break up when you remove the plant from the pot and so has less of a shocking effect on the plant.