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Overwintering Tender Bulbs

By Liz Case,  Master Gardener 


Plants and bulbs which are not hardy to our zone have to be protected, 

  • Definition of a “tender bulb”  -  non-frost hardy bulb -  can be a Rhizome, Tuber, Tuberous root, or a Corm
  • A Rhizome is a thick horizontal stems, roots grow from the bottom, leaves & flowers sprout from the top  (e.g. Calla Lily, Canna & even Lily of the Valley)
  • A Tuber  is a fleshy underground stems that have eyes or buds from which leaves & flowers grow like potatoes, begonias and caladiums (elephant ear) 
  • A Tuberous root  are swollen, fleshy roots;  have a pointed bud on top and roots that sprout from the bottom (e.g. Ranunculus & Dahlias, are produced by division of root tissue, not stem tissue.  Leaf buds form at the junction of existing stems on each division piece.)
  • A Corm  will last one season and reproduce by growing a new corm on top of the old one (e.g. Gladioli)


  • Shortly after first frost, (? 2nd week Sept.) and bruising and die back has occurred and while the ground is still workable (pick axe not recommended) lift plants, if a sunny day spread out in the sun to dry for the day, knock the dry soil off the roots.   If not sunny, bring indoors allow to dry for a couple of days, knock off soil 
  • Label as you go
  • Box, Vermiculite (quarried S. Of Gooderham on 507!), or Dry Peat Moss, Cedar shavings (sand is not so good)
  • 1-2” Layer at bottom, lay them on top, adding another 1-2”, keeping them an inch or so apart to prevent rot & disease spreading.  Adding successive layers until the box is full.
  • Cover with thick layer of newspaper 
  • Store in cool dark location (above 35 F , 2C )
  • Check regularly, (every month) if bulbs show signs of desiccation i.e. drying out too much, sprinkle a little water over the newspaper
  • End of Feb./early March can remove from box 
  • Plant into individual pots, keep indoors until all danger of frost is past – & soil is workable .....then plant out