Complex sentence: Control of slugs is essentially done in the spring, as each surviving slug can result in about a hundred new slugs, the amount of slugs can also be greatly reduced by not keeping a compost heap too near the garden.
Split into simpler sentences: Control of slugs is generally done in the spring, as each surviving slug could result in about a hundred new slugs. The amount of slugs can also be greatly reduced by not keeping a compost heap too near the garden.