Cultivators, tillers and rotavators are usually four-stroke machines and you should therefore ideally use SAE 30 Oil, which is used and sold by most manufacturers, including Briggs and Stratton. *
You can use 10w/30 oil, but this is thinner than the SAE 30, and therefore flows more easily in cold weather. However, some experts say it is too thin and the SAE 30 lubricates better, being more viscose.
SAE 30 does a better job of lubricating the parts in a hot engine and 10w/30 usually costs more, but flows easily when cold (so makes it possibly easier to start).
*N.B. A few machines are fitted with 2-stroke engines and will, obviously, require a mix of 2-stroke oil and fuel. Check your manual, which should give more information on this and see our article Basics of the 2-Stroke Engine in our maintenance section.