Florida researcher Ute Albrecht shared information about citrus tree roots at the recent Georgia Citrus Association annual conference. The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) associate professor specializing in plant physiology discussed rootstocks and soils, suggested transplanting tips and touched briefly on freeze tolerance. Albrecht works at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
Rootstock selection should be based on compatibility with the scion, soil characteristics, pest and disease pressure, desired size control and spacing, and other desired traits, Albrecht said.
She reported that US-942 was the most budded rootstock in Florida in 2018, 2019 and 2020. There were almost 1.3 million buddings of US-942 in 2020. In both 2019 and 2020, the next three most popular rootstocks in Florida were Kuharske, X-639 and Swingle.
Roots are unable to grow into soils of high bulk density/compacted soils such as fine sands and clays, Albrecht reported. She said roots need oxygen to respire and produce energy. Flooded and compacted soils have little oxygen.
Albrecht offered numerous transplanting tips, including:
- Inspect trees before purchasing and planting.
- Plant trees the same day they are received.
- Don’t allow trees to dry out.
- Loosen the potting medium to expose roots to the soil.
- Pot-bound roots need to be pruned/slashed to encourage new growth.
- Plant roots so they are in direct contact with surrounding soil.
- Plant trees slightly above the surrounding soil. Don’t bury the graft union.
- Don’t throw fertilizer in the planting hole.
- Water-in trees immediately after planting.
Albrecht briefly mentioned factors affecting freeze tolerance in her talk to growers who experienced freezes in December 2022 and January 2023. Those factors were:
- Grove location and topography
- Minimum air temperature and duration
- Freeze acclimation
- Species and cultivar of scion and rootstock
- Condition of the tree
- Presence or absence of overhead or ground cover
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