This really depends on the model you buy, as every small garden tiller is different. The Earthquake 20015, for example, can till up to 11 inches down into the soil, whereas the TOYPOPOR Mini Twist Tiller can only go about 3.8 inches deep. The tilling depth of your model is an important factor to consider, and a lot of it depends on the type of tiller you buy. Rear tillers tend to be able to go about 10 inches down on average, and the same applies to front tillers, whereas mini manual tillers can only go around 6-8 inches deep. It is possible to find models that can go beyond 10 inches in depth, but you don't really need to go any further than this to provide good soil conditions for your vegetable garden.