In 2011, dry and hot conditions in July resulted in ginseng berry abortion in fields not irrigated at the onset of moisture stress. To prevent the same issue from occurring this year, it is important to time irrigation properly, especially in those gardens intended for seed production. Recent rainfall has resulted in good soil moisture in most gardens, but this can rapidly change with an extended hot and dry period. In 2011, most gardens had excessive moisture to the middle of June but had moisture stress by early to mid-July.
No studies have been conducted to identify critical times for irrigating ginseng for seed production, but some principles from other crops likely apply to ginseng. The most critical time to irrigate any crop for seed production is at bloom. Because ginseng flowers do not all open at once, there is an extended period in which adequate moisture is important. Lack of moisture at bloom will result in poor or no pollination and minimal seed production.
Once pollinated, a viable seed can still develop with mild moisture stress. However, moisture stress can lead to smaller seeds, which will affect the vigour of the resulting seedlings later on. Anything beyond a mild moisture stress will result in berry abortion. This is likely a response of the plant to ensure survival of the root at the expense of seed production.
In gardens not intended for seed production, moisture stress results in poor root growth and potentially increased susceptibility to disease. When the plant does not have adequate moisture, the stomates (small openings on the leaf) are closed, which prevents moisture loss from the plant. This also prevents the air exchange required for photosynthesis. This can also occur under heat stress. As a result of a shut-down in photosynthesis, very little root growth occurs under moisture stress. Initially this occurs only in the afternoon when transpiration is at its highest, but eventually can occur for most of the day.
Always monitor soils in ginseng gardens for moisture content and ensure consistent and adequate moisture for both root and seed development.