Expert: Kenneth Joergensen - 5/4/2004

Question
Hello.  First let me tell you, that I live in Houston, Texas, Zone 8 and my zip code is 77083.  My question is this: I planted some Cannas four years ago.  The first year I received somewhat good blooms, the second year, no caterpillars, no disease, just beautiful humongous blooms with wonderful foliage, then the third year, last year, they seemed to get a lot of rust on the leaves with caterpillars on the leaves. I dunno why, but I suspect because of so much rain and because they had multiplied so, possibly not enough air circulation to be healthy.  So I divided them, some in the fall of 2003 and the early spring of this year 2004 hoping that this year would give me great results. Well, here is the question, if I divided them, giving them more air circulation, why are they giving such small flowers? I add organic matter each year and the soil has only a few worms it seems and I've only fertilized once since April this year.  Can you help?  They are my prize possession in my front garden and they are giving luscious green leaves, but small flowers. Thanks for the help.

Answer
Cannas are very gross feeders. the organic matter is very good, but I would use a regular flowering plant fertilizer several times during the growing season.

Cannas as we know them today are nothing like they used to be many years ago in the wild. the hybridized versions consume a lot more fertilizer than the original plants in the wild (but the flowering was also different). For these plants, use 10-10-10 fertilizer every 45-60 days, or apply OSMOCOTE 14-14-14 (slow release) or Multicote 14-14-16 (slow release, aka rose food) 2-3 times per growing season (approximately every 90 days).

The plants probably lived off their fat tubers for a few years only to languish now due to depletion. Fertilize these tubers regularily every year.

As to fertilizer:
Lushious green leaves but few and small flowers can also be due to the use of high nitrogen fertilizers. If your compost/organic matter is high in nitrogen but low in phosphorus/potassium (which some composts may be) you are promoting lush foliage at expense of flowers. If you have put lawn fertilizer down near the plants (or accidently into the flower beds) it would also explain it.

I think it more sounds like you need to start fertilizing to begin with, but just remember that lawn fertilizer near the flower bed can interfer with flowering. When it comes to compost, I strongly recommend topdressing with it, but avoid compost which had lots of cow manure in it. Now, I am not saying to stop using compost - I am not - but avoid digging in a 6" layer of composted cowmanure. You are better off placing a 2" layer of composted forest products (fall leaves) on top.

Finally, make sure you are watering once or twice per week deeply (throughly wet the root zone) in case of lack of rain. sometimes small flowers are the result of draught induced stress during early spring flower formation.