Growing Garlic on Clay Soil 4 Comments

Clay soils can be a challenge when growing almost any type of vegetable or crop. This is especially true when trying to grow garlic because it has some special requirements.

Clay soil takes a long time to warm up in spring, drains poorly, turns rock hard when dry, and makes big clumps if tilled when wet. This often means that vegetables have trouble growing in them without special care.

Benefits Of Growing On Clay

With all the challenges growers face with planting in clay soil, why would anyone decide to try and grow garlic on them? The fact is, most people don't get to choose where they garden or farm and they have to do the best they can with whatever soil they end up with.

Also, even though clay soils can be challenging to work with, garlic usually grows very well on them if conditions are managed properly. Due to their high fertility and consistent moisture availability, clay soils have the potential to grow some of the largest garlic bulbs possible. On our farm, the garlic grown on clay soil consistently yields better than the garlic grown on sandy soil.

Clays are formed from tiny sediments on the bottom of ancient lakes or on the floodplains of rivers. These extremely small particles have incredible adhesion to water, nutrients and each other. 

This is what makes clay soils highly fertile and gives them the ability to hold onto very high amounts of moisture, mitigating drought conditions during dry periods. In fact, clay is so good at holding moisture, that it holds onto and makes available to the crop almost 4 times as much water as sand. This is why crops grown on clay soils often do not require any additional water during the growing season.

Drainage & Water

All of this moisture-holding capacity and fertility comes at a cost though, as anyone who has worked with clay already knows. It can be very hard to manage and be unforgiving when conditions are too wet or too dry. This means that it is very important to plan ahead and be prepared for less than ideal weather conditions before they happen.

The biggest challenge with clay soils is dealing with wet conditions during  planting and harvest time. Prolonged wet periods at planting time can cause delays and in some extreme cases prevent planting all together. During the growing season, overly saturated soil can cause the garlic to become stunted or promote bacterial rots that can kill the plants. This is why it is very important to have good drainage before planting garlic in a new area.

Tasks such as weeding and harvesting can also be difficult when conditions are very dry. Moderately watering can help soften the ground and make working with the soil much easier. When watering clay soils, it is best to wait until the surface has dried to prevent compaction and damage to the soil structure.

Adding Organic Matter

Soil organic matter serves as a reservoir of nutrients for plants, helps with soil aggregation, increases nutrient levels, holds moisture, reduces compaction and minimizes surface crusting. These are all attributes that help improve clay soils and makes them easier to work with.

Even though clay soils tend to be naturally higher in organic matter than sandy soils, soil conditions can still be greatly improved by adding large amounts of organic amendments (peat moss, manure, compost, etc.). Overtime, organic matter will build up and enhance the soil conditions.

When using organic amendments such as manure or compost, be sure to add them to the soil in the summer or early fall, well before planting the garlic cloves. This will ensure that the organic materials have a chance to be incorporated into the soil and begin releasing their nutrients before the garlic starts growing.

Adding Fertilizer

Most soils have 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. Although clay soils tend to be naturally fertile, especially when organic amendments such as compost are added regularly, they are still usually low in Nitrogen and sometimes other nutrients as well.

The best way to determine your soil's fertility levels is to take a soil sample and see what the results show. If you your soil test shows low nutrient levels or you are unsure as to how fertile your soil is, you can add high nitrogen or general purpose organic fertilizer. This works best when used with additions of compost or manure.

For more information on fertility, see our How To Fertilizer Your Garlic page.

Using Raised Beds

Raised beds warm up the soil earlier in spring, help with drainage issues, improve the soil structure and allow the application of fewer amendments such as manure, compost or fertilizer. Also, raised beds allow you to have footpaths or wheel tracks between the growing rows. This helps minimize the soil compaction that occurs every time you have to do garden or fieldwork.

Beds should be made between 4 and 6 inches high and have between 2 and 4 rows planted per bed, depending on the width of the bed. In a garden, beds can be made by moving the soil from the footpaths into the center of the bed and then levelling the soil to make the top of the bed flat. For large areas tractor pulled equipment can make the beds

Planting Cover Crops

Growing crops that have extensive root systems such as deep-rooted sweet clove or fibrous annual rye prior to planting garlic can improve soil conditions tremendously. Deep rooted plants help with internal drainage and fibrous plants with massive root systems improve soil structure making the clay behave more like a loamy soil.

Since garlic is planted in fall, cover crops should be grown during spring and summer prior to the garlic being planted. This will allow enough time for the cover crop to full mature, adding large amounts of organic matter and then subsequently worked in before fall. 

For more information on growing garlic see our other blog articles or growing garlic guide page.

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.