The Collaborative International Dictionary of English v.0.48:

Tiller \Till"er\, v. i. [imp. & p. p. Tillered; p. pr. & vb.
   n. Tillering.]
   To put forth new shoots from the root, or round the bottom of
   the original stalk; as, wheat or rye tillers; some spread
   plants by tillering. [Sometimes written tillow.]
   [1913 Webster]