Garlic Almanac and Phenotypic Plasticity

Silverwhite Silverskin garlic
Photo Southern Exposure Seed Exchange

Garlic Almanac and Phenotypic Plasticity

(How garlic adapts to its locality)

It’s garlic harvest season for many of us and I notice many growers are searching my site for information. Here are quick links.

Garlic signs of maturity from October 2020

Everything You Need to Know About Garlic includes all the links listed below here.

Much about garlic is to be found in my Alliums for the Month Series:

Garlic harvest.
Photo Twin Oaks Community
Other posts about garlic, starting with harvest:
Pulling garlic scapes.
Photo Wren Vile

Phenotypic Plasticity

Phenotypic plasticity of garlic refers to the changes to a garlic variety grown in a particular location. Genetically identical garlics can grow differently in different environments. Garlic reproduces asexually, the new cloves are all clones of the mother plant, with no new genetic material introduced. And yet, over time, garlic saved and regrown each year in a certain locality will adapt itself to that location, due to the particular soil type, water availability, local temperatures, latitude, altitude and cultural practices. For example, studies have shown that varieties grown in drought-prone areas can, over years, develop more drought-tolerance. Commercial cultivars can have the highest bulb yield under well-watered conditions, but drought will show up the adapted strains in a comparison trial.

Garlic Plants
Photo credit Kathryn Simmons

We have been growing our own strain of hardneck garlic for over 30 years, and it does really well here. Originally the seed stock was a bag of garlic from the wholesale vegetable market. This is the very thing we are told not to do, as it may introduce pests and diseases. Indeed, it may, but our original folly is now deep in the past, and we have fortunately seen no problem.

I was reminded about phenotypic plasticity, when a friend and neighboring grower reported that the seed garlic we had passed on to her was doing well and was mature a couple of weeks before the variety she normally grows.

From the 2004 work of Gayle Volk et al, Garlic Seed Foundation analyzing 211 garlic accessions, we have learned that there are many fewer genetically distinct varieties of garlic than there are named varieties. Of the 211 accessions in that trial, only 43 had unique genotypes. But garlic shows high biodiversity and ability to adapt to its environment. The same garlic genotypes in different environmental conditions can show different phenotypes. This demonstrates the high phenotypic plasticity of garlic, probably linked to its complicated genetics, which somehow compensate for lack of sexual reproduction.

Work done in 2009 by Gayle Volk and David Stern, Phenotypic Characteristics of Ten Garlic Cultivars Grown at Different North American Locations  addressed the observation that garlic varieties grown under diverse conditions have highly plastic environmental responses, particularly in skin color and yield. This is a very readable paper for non-academic readers. Ten garlic varieties were grown at twelve locations in the United States and Canada for two consecutive years to identify phenotypic traits of garlic that respond to environmental conditions. The purpose of the study was to determine which phenotypic traits are stable and which vary with location.

Inchelium Red softneck garlic – note the small cloves in the center.
Photo Southern Exposure Seed Exchange
  • Clove number, weight and arrangement, clove skin coloration, clove skin tightness and topset number, size and color stay true to variety independent of location.
  •  Mostly, varieties classified as hardneck types produced scapes and those classified as softnecks did not, but there were some exceptions.
  • Bulb size, bulb wrapper color and bulb elemental composition (flavor) are related to location, (the influence of the local environment, such as the weather in that production year and the soil mineral content), rather than variety. The intensity of the skin patterns is highly dependent on the location. Some general trends were noted, but no clear correlation was found. (Read the study for the details).
  • For good size, predictably colored and flavored garlic, buy seed garlic grown locally that yields well. When garlic is grown in similar conditions to those in which it was produced, yields can remain consistent or improve.

    Our softneck garlic in May.
    Photo Pam Dawling
  • Varieties that grow well thousands of miles away are not a guarantee of a good result in your garlic patch. They may not match the bulb size, shape, color and flavor listed in the catalogs.
  • When grown under the same environmental conditions, the leaf number before bolting, flowering date, the final stem length, the flower/topset ratio, and pollen viability vary from one variety to another.
  • Studies that compared bulb firmness, pH, soluble solids, moisture content and sugar content with appearance determined that many of these traits are independent of skin color across 14 garlic varieties.
  • Bulb size was highly dependent on growth location with northern sites producing larger bulbs overall than southern sites for at least half of the trial varieties. Regional differences between varieties with respect to bulb size were noted, but because the project had a limited number of sites, specific variety recommendations for different regions were not provided.
  • Bulb size and weight were positively correlated with soil potassium levels.
  • Bulb sulfur and manganese content (flavor) were correlated with soil sulfur and manganese levels.

    The famous Music garlic, a hardneck type – see the stem.
    Photo Southern Exposure Seed Exchange
  • The demand for high-quality fresh garlic is increasing as restaurants and consumers seek out local vegetables. Consumers are attracted to colorful, unique garlic varieties for different culinary uses. As variety name recognition in garlic increases, understanding which traits define particular varieties and which traits vary within cultivars, depending on environmental conditions, will be valuable for successful marketing of new garlic types.