I have found that different techniques work for different plant species
depending on the presence of polysachs, phenols, oils . . . there's a
web site for a journal called Biotechniques that would be a good place
for you to start looking for different protocols.
If CTAB protoco is not giving you good quality DNA, try some of the
protocols from these authors:
Wang et al. 1996. An improved isolation of nuclear DNA from leaves of
wild grapevine dried with silica gel. Plant Mol Biol. Reporter
Tabaeizadeh Z., Agharbaoui Z., Harrak H., and Poysa V., (something about
transgenic tomatoes) 1999 Plant Cell Reports 19:197-202
Bernatzky & Tankley Genetics of Actin related sequences in tomato. 1986
Theor Appl Genet 72:314-321
Prince, J. something about DNA extraction from peppers.
Hope this helps,