Garlic grows best with a moderate level of nitrogen and potassium but it will also need phosphorus, magnesium, and sulfur as well – just in smaller quantities than the first two, and the nitrogen and potassium are the most important. Now that you know, just be sure that your chosen companions won’t be competing for these same resources or if they will, be sure that the companion is a light feeder so that you can supplement the soil accordingly to make sure that both plants get what they need.