Hydroponic Strawberry Propagation


Types of transplants

There are various types of transplants available for strawberry production. Growers need to carefully decide the type to introduce in their growing systems. Many cultivars available in the US are proprietary, which requires an appropriate license agreement to propagate. Therefore, consult your local extension agents specialized for berries to find a nursery reasonably near your production site. Depending on the season, getting the best quality transplants is often challenging. Therefore, seed propagated cultivars are an attractive option for small, off-season operations. However, number of seed propagated cultivars is still limited and may not be the best performing cultivar in your production system. Small scale trials for cultivar selection are always recommended before expanding the production with any new cultivar.  

Rooted runner plugs. These plants are also called ‘misted runner plants’ grown from ‘misted runner tips’. These plants are typically propagated in summer and have not experienced any kind of storage process.  Mother plants are grown in a trough placed high (2 meter) above the ground and the runners allowed to grow and hang down. After enough daughter plants are produced, daughter plants with root initials are excised and rooted in fresh substrate in a cell tray or small pot under frequent misting. When plants are excised from the runner, Japanese growers typical cut the proximal side runner (stolon) longer than distal side runner, so that it will serve as a guide to plant them tilted outwards in the trough (Nobunkyo, 2008). Under frequent misting, rooting will occur within 5-10 days. Grow them out to have 3-5 true leaves and 1 cm or greater crown diameter before planting into your production system. 

Conditioned plugs.  For short-day cultivars, misted runner plants with established vegetative growth can be treated under low temperature and short day condition to induce flower bud initiation.  A typical practice widely used in Japan is to move these plug plants to a cold room (15°C, dark) for 14-16 hours every evening for a period of 3-4 weeks in order to assure an early harvest (such as October or November).  Flower initials are confirmed under microscope before final transplanting.

Frigo plants. These bare-rooted plants are dug out from the field in early or mid winter, trimmed to remove leaves and some root length, and stored at -1.5°C for many months.  In North America, frigo plants are typically single-crowned plants and the storability is often limited to 5-6 months (June is the typical end of frigo availability in North America). However, in Belgium and the Netherlands, frigo plants are multi-crowned plants grown from misted runner tips and have a longer storability (e.g., 10-11 months), presumably due to much larger carbohydrate reserve. The frigo plants already have flower initials developed prior to the long storage and so quickly produce fruit after transplanting, allowing off-season production.  These well-established multi-crowned frigos (with one primary crown and lateral extended crowns) are also referred to as ‘tray plants’ (with ~250 mL substrate volume per plant) suitable for producing a large flush of fruit at a targeted short production cycle (Peter Melis, Personal Communication).  Flower initials and their developmental stages of tray plants are evaluated under microscope and this ‘flower mapping’ is considered as a key service to assure highly productive off-season strawberry production in Europe. Some cultivars, however, have limited storability. For example, prolonged storage of ever-bearing or day-neutral cultivars sometimes hinder them from developing flowers, which may be another reason why frigo storability is limited in North American strawberry nurseries.

Green plants.  These bare-rooted plants are dug out from the field in early fall and typically used as planting material in Florida. For short-day cultivars, plants still need to be exposed to photoperiod and temperature suitable for flower initiation.

Seeds. Seed propagated strawberry cultivars are often hybrids of selected parent cultivars that are near-isogenic lines (NILs). There are several cultivars available in North America but commercial use seems to be limited. Developing NILs in strawberries is a time-consuming process as strawberry has long been propagated vegetatively and has complex polyploidy (8X). Despite the challenge, there have been intensive efforts made in Japan to introduce seed propagated cultivars commercially.  Ability of growers to start plants from seeds will become an attractive alternative for off-season strawberry production or in urban greenhouses.

(Updated 6/27/16)

Photo credit: Strawberry Fields, Japan