When is the best time to plant garlic?

            Garlic yields best when it is planted in the fall and has time to achieve some root growth before winter. Historically, planting around the date of the first fall frost has been hypothesized as being the best time to plant to reduce the chance of winterkill and get good root establishment before the ground freezes.

            The ability to plant weeks before the first fall frost would give a longer window for planting, which is an advantage when there is a large acreage to plant or in fields that have heavier soil and take time to dry before mechanical planters can be used.

            The concern with planting too early is that the plant emerges and produces multiple leaves before the ground freezes. These leaves may die from extreme temperatures and leave the clove with little resources to put a new sprout up in the spring. Without enough energy to push new leaves to the surface in the spring, the plant dies.

            Many growers planted way after the date of the first fall frost this year since the ground was too saturated from frequent rains, pushing many acreages to be planted into November and December. Lack of root growth resulting in frost heaving may also result in greater amounts of winterkill and decreased yields come harvest in July.

            To determine if planting earlier would result in winterkill or have negative impacts on yield, a planting date trial was set up in Dashwood, ON in 2022 with seven planting dates starting August 30^th and continuing roughly every three weeks until December 6^th, along with a single planting date in April 2023. Despite not missing any planting dates, several planting dates would have been too wet to plant mechanically if we were not planting by hand (Figure 1).

            Bulbs of a porcelain cultivar, similar to Music, were split into cloves immediately prior to planting every three weeks, from the same source of bulbs throughout the entire trial. All cloves were planted between 5-10 cm (2-4 in.) deep and covered with 2-5 cm (1-2 in.) of soil in a randomized, complete block design.

            The 2022 winter was relatively mild for Dashwood, but there was limited snow cover to provide some extra protective insulation. The middle of the trial (replicates 2 & 3) was flooded and underwater for a few days in the early spring. This likely explains why many of the cloves planted after October 27^th that did not have sufficient root development did not survive.

            These results are limited as they are only from one year, a single field site, in one soil type, with a relatively mild winter. The best performing planting date was September 14^th based on the number of plants that survived and their dry weight at harvest (Figures 2-3). The September 14^th planting date was not significantly different than the August 30^th or October 5^th planting. The largest bulbs came from those planted August 30^th, but it was not significantly different from the three following planting dates.

            The average date of the first fall frost in Dashwood is October 13^th based on the Average Frost-Free Period in Climatic Zones of Ontario (1975-2005). Planting August 30^th would be almost 6 weeks before this ‘ideal’ time to plant. Despite the plants from the August 30th planting having 3-4 leaves prior to the ground freezing, the results indicate that this did not negatively affect survival or yield (Figure 4). Planting this early gives a much larger window of opportunity to get the crop planted, especially in soils that take time to dry out.

            For those who have planted garlic earlier in the past and experienced winterkill, was the planting stock compromised or weakened in any way? Were there stem and bulb nematodes present? Were the bulbs cracked greater than 7 days prior to planting?

            Planting earlier in the season may still put the plants at a higher risk of winterkill if they bolt, so it is likely best to avoid taking this risk if you are planting compromised / weakened planting stock.

            Currently, this trial is being repeated and six out of the seven planting dates have already been planted in 2023. We also added additional treatments and intercropped oats at the same time as the garlic was planted for the August 30^th and October 3^rd plantings. Potentially the oats can help limit soil erosion over the winter and maybe the remaining plant material can provide some early season weed suppression in the spring.  

The full report can be downloaded here: 2022-2023 Planting Date Trial