Rooting Strawberry "Tips" to Create Plugs

Steve Bogash (smb13@psu.edu) and Kathy Demchak (kdemchak@psu.edu), Penn State Horticulture and Extension

1) Use tips only from a reputable source. Tissue cultured mother plants are the preferred source. Using tips from your own or other local fields can create future problems, as there is the potential to move diseases and mites from field to field. Also, many varieties are patented and require licensing in order to take cuttings. USDA varieties are not patented, and can be propagated at no charge.

2) Ideally, tips should be planted as soon as they arrive. However, if this is not possible, the tips may be stored at 34˚F and 75-80 percent humidity for up to two weeks from the date they were harvested from the mother plants. If you're in a pinch for time and cooler space, pack the plants in ice. Allow 35 days from planting to grow a field-ready plug. Trim any runner cord to a 3/8- to 1/2-inch stub before planting.

3) Carefully cull the tips you are going to plant. Anything that looks at all questionable should be discarded.

4) Sort tips by size. Do not plant small and large tips in the same trays, as the smaller plants are likely to get shaded. The smaller plants in this now lower canopy in the flat are ripe for botrytis and powdery mildew as air circulation will be poorer in the lower canopy.

5) Plant the tips in plug trays with 50 cells per tray. Use a sterile media designed for rooting herbaceous "bare-rooted" plants. This includes most professional grower mixes. If you are recycling trays, be sure to remove all organic matter from them, then chlorine dip (one part liquid bleach to nine parts clean water) the trays prior to use. Be careful to avoid contamination of the propagation area.

6) The hook on the tip should be just in the potting media. Do not bury the crown.

7) Do not fertilize just planted tips. The fertilizer charge in most potting media will be sufficient until the plants are well-rooted. Fertilize for the first time at two weeks after planting using 100 parts per million (ppm) of nitrogen with calcium nitrate as the source, and repeat at weekly intervals. If you are holding the plants for longer than four to five weeks (thus creating super plants), switch to 20-20-20 at 100 ppm of nitrogen for later applications.

8) Your goal is to keep the leaves moist until the tips start to create their own roots. Hot, sunny days will require extra mist, while cooler, cloudy days less mist. The assumption with the following misting regimen is that you will be placing the new tips in a greenhouse or high tunnel. Enclosed structures will require less misting as wind will not dry the leaves as with plants growing outdoors. Do not allow the surface of the leaves to dry for the first seven days. Mist using fogger nozzles of an intermediate discharge rate. Start with the following misting regimen, but adjust it as needed to prevent over-watering or desiccation of the leaves:
a) Time for the system to reach operating pressure needs to be factored in as this regimen assumes actual misting time.
b) Day 1-7: Use five seconds of mist every 15 minutes.
c) Day 7-12: Gradually reduce misting. Keep the media moist. Misting should be terminated by the end of this period.
d) After week three, the plants should be well-rooted and ready to begin conditioning for field planting. Keep the
    media moist, but expose the plants to full sun by setting them on a field wagon or on groundcover fabric. Keeping  
    them in a greenhouse or high tunnel is okay, but do not mist and maintain good airflow.
e) Do not mist after sundown, even at first. Some growers believe misting after sundown can create bigger plugs, but 
    the greater chance of disease offsets any possible benefits.

Additional recommendations:
•    Plants can be rooted in either an enclosed structure (greenhouse/high tunnel) or outdoors. If outdoors, choose a protected location to keep the unrooted tips from being dislodged by wind or heavy rain. Be sure to put down a layer of groundcover fabric before rooting plants outdoors. Make sure your misting set-up is working ahead of time.

•    Shade cloth can be used to limit plant desiccation, but is not recommended. This will slow the time from sticking the tips to having field-ready plugs by about a week.

•    Soil inoculants such as Plant Shield and Mycostop may be advantageous in preventing soil-borne diseases. However, no definitive research has been done using these products on strawberry tips at this time. In other crops, these products have prevented a wide range of soil-borne diseases.

•    Due to the constant misting, control of diseases should be managed primarily with good ventilation. Any fungicides that are applied during the time the tips are being misted will be washed off too quickly to accomplish anything. However, a fungicide application to the plants prior to planting is probably a good idea.

•    Scout the plants for spider mites. Their eggs are tiny so use a hand lens. If any eggs or mites are found, treat before planting in the field. Materials for two-spotted spider mite control include: Vendex, Acramite, Oberon, Kanemite, Portal and Zeal. Zeal is only for eggs and immatures. As always, growers should closely follow label restrictions and requirements.

Thanks to Dr. Frank Louws at North Carolina State for disease control pointers and to David Lankford, formerly of Davon Crest Farms, for many helpful suggestions.