Those instructions are for people who want to divide their dahlias during the winter. In San Francisco you should be able to leave your dahlias in the ground year round.

I hope I can. We do get a lot of winter rain, and if we don't I still have to water the other plants near them. I don't have bed dedicated to the dahlias only. So, they may to rot, but the soil is very sandy and well drained. I only have two dahlias.

only two dahlias I didn't think that was possible. I have been told it is the wet out there that kills your dahlias. Let us know how you make out and get way more dahlias next year.

Two is enough because the stems are a bit weak and I have a full line up of plants. The flower do have to be staked making them high maintenance plants. I will post back if they live. I think they could grow bigger next year with more time for development and maturity.

In your climate dahlias may not even go dormant in which case rot should not be a problem if they the plants are still alive and growing during your mild winter. If they do go dormant you could try covering the ground above the tubers with plastic sheeting to keep the winter rain off, that would help prevent tuber rot.

I live about 50 miles south of SF and have 2 dahlia plants in pots placed near flower beds. They still have small buds on them, but many leaves have fungus, probably from the flower beds' overspray. I have 'drip' in the dahlia pots. Does anyone know how I should treat the fungus and what I need to do with the plant over the winter. This is my first attempt in dahlias. Thanks so much.

I ive in the PUget Sound area of Washington state and I mostly leave mine in the ground over winter. The 3 big problems that one might encounter are (1)freezing--turns the tuber to mush, no chance of future use (2) rotting in soggy soil...soil must be well drained (3) damage by underground rodents (Hungry mice) and Insects like slugs that will eat emerging growth off them and even down into the tuber, sometimes leading to rot. If you have a pile of tubers from more then a years growth since dividing, often the top ones will freeze but the bottom ones remain intact and growth will come from them.
IN your climate, David, they should be fine. You should divide the clump of tubers ever two or 3 years through to keep your plant strong. I dig them in the spring, divide and repot into my greenhouse to speed them up and get some good growth before the soil warms in the garden. You can even take an axe to the clump and simply quarter it and cut off the cut surfaced ones and plant the rest of the quarters into 4 different locations or give them away.I second the idea of covering your plant's space with plastic over the ground.

They died back to just nothing, but I have to see if they will began to sprout again. I have bad luck with bulbs rotting when I dig them up and usually better with leaving them in the ground. They get this white moldy stuff and then they shrivel up and turn black and mushy.