How to Fertilize Your Garlic Properly

Piles of compost in garlic field
Piles of composted manure being applied to a field before planting garlic.

Heavy Feeder

Garlic is a heavy feeder and requires high soil fertility to perform at its best. When nutrients are at optimum levels, plant growth is healthy and bulb size is maximized. Poor soil fertility is one of the most overlooked factors affecting garlic bulb size at harvest and can be easily avoided with proper planning.

Many inexperienced growers believe that adding a thin layer of amendments such as compost is enough to meet the fertility needs of their garlic. They sometimes also believe that a “healthy application” of manure several years prior is adequate. Although it is true that soils benefit greatly from adding organic matter, it does not necessarily mean that nutrient levels will be high enough for the garlic to reach its full potential.


Soil Testing

The best way to measure fertility is to take a soil sample and send it in to be tested. Soil testing is always recommended no matter how large or small the growing area. This is not hard to do and there are many labs across Canada and the United States that growers can submit soil samples to.

Often growers who use organic or natural methods feel that they don't need soil tests. This is not a good practice and can often lead to deficiencies in certain nutrients or even over-fertilization without realizing it.

If you don’t have a soil test to tell you how much fertilization is required, assume that your soil has very low fertility (close to zero). Although this is not ideal and may provide your garlic with more nutrients than required, it will prevent any deficiencies. 

One exception to this is for soils that have been heavily amended for many years such as well-managed gardens or highly fertile planting areas like old manure piles and livestock pens. These soils are very unlikely to require any additional fertility and adding fertilizer or manure will have no benefit.


Fertility Rates

Most soils are naturally low in Nitrogen and depending on the locations, other nutrients as well. They also have often been depleted from years of farming. Even the soils in many urban yards were once heavily farmed until ultimately finding their way to someone’s garden. This means that they need some additional care to improve their fertility and grow the healthiest garlic plants.

These are general fertility guidelines that can be used for most locations. They could be lower or higher for you depending on where you live and the type of soils you have, but they can serve as a good starting point. The following amounts are the recommended levels of nutrients in the 0 to 24-inch depth portion of the soil:

Nutrient

Pounds per Acre

Pounds per 1000 ft2

Nitrogen

120 lbs (55 kg)

3 lbs (1.3 kg)

Phosphorus

160 lbs (73 kg)

4 lbs (1.8 kg)

Potassium

150 lbs (68 kg)

4 lbs (1.8 kg)

Sulphur

30 lbs (14 kg)

1 lb (0.5 kg)

Fertility recommendations for growing garlic. 


Timing of Applications

Phosphorus, potassium and sulphur should be applied and incorporated before planting. Nitrogen should be split into several applications with 1/3 being applied at planting and 2/3 during the growing season starting in spring. After the first spring application, nitrogen should be applied every 2 to 3 weeks until the scapes emerge.


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Over Fertilization

It is important to not over-fertilize the garlic with Nitrogen as this can cause excessive top growth. Similar to other vegetable crops, too much top growth often leads to small bulbs because the plants are too focused on producing leaves and not storing energy below ground. The goal of fertilizing is to apply just enough nutrients to grow healthy plants without causing excess leaf production.

Overfertilization can also cause damage such as burning to the garlic plants, especially when they are young. This can happen with either synthetic sources of fertilizer such as urea or organic fertilizer sources such as fresh chicken manure.

Growing conditions such as hot weather or drought can increase the sensitivity of the plants to fertilizers. Watering the garlic after fertilizing is recommended to help prevent any issues and move the nutrients down into the soil where the roots are.


Nutrient Sources

Soils that have low nutrient levels can have their fertility increased by adding either organic amendments such as manure or with commercial fertilizer such as granular and liquid soluble products (for example, Miracle Grow). No matter what the method of fertilizing is (organic or synthetic), the overall goal of trying to feed the garlic with optimum nutrient levels is the same.

When using organic sources to fertilize your garlic, they should be added in the late summer or early fall before planting the garlic cloves. This will ensure that the organic materials will have a chance to be incorporated into the soil and begin releasing their nutrients before the garlic starts growing.

As a general rule, compost and manure that has been incorporated into the soil will release most of their nutrients over three growing seasons. Some growers apply a large amount every three years, while others apply a large amount the first year and then a smaller amount (1/3) every year after that.

Also, composts and manures tend to be low in Nitrogen and therefore require very large amounts to meet the complete needs of the garlic. There are some organic products such as pelletized manure or liquid fish fertilizer that are high in Nitrogen and can be used to supplement the other amendments if needed.

Benefits of Organic Matter

It's important to note that all soils, regardless of fertility levels, benefit from adding large amounts of organic matter such as compost. Garlic grows very well in soils with high organic matter and benefits more than most vegetable crops to the addition of amendments.

Organic matter holds onto excess nutrients and slowly releases them over a number of growing seasons. As well, it is extremely effective at improving soil structure and filth. These are all factors that help garlic plants reach their full potential for growth.


About the Author: John Côté owns and operates John Boy Farms with his family who have been farming the same land for over 140 years. As an agronomist and experienced farmer, he helps other growers learn how to grow garlic successfully. He has written many articles and is the author of The Master Guide to Growing Big Garlic.