sweet potato is a perrennial where i live! great what do i do now?

i just recently learned that i can grow sweet potatoes as a perennial in zone 9b and so what does that mean for when i want to harvest? if i dig them all up then there is no way that they will come back in the spring right? in the same article i read about it being a perennial, it also said not to plant them more than two seasons in a row to avoid the rootrot nematode. that makes no sense to me. if its a perennial then it stays there forever, right? before i found out it is a perrennial i was going to put beans in the bed where the sweet potato is right now. next question is when i am going to plant the beans, i was just going to cut back the vines and put the beans in right next to the sweet potato, but then i was thinking that wont work because i think i should harvest on 9/15/15. i say this because the SP went in about 5/15/15 and everybody says that it takes them 4 months to fully mature, SOOOO if im planning on harvesting on 9/15/15 , then OBVIOUSLY i cant have bean seedlings getting in my way, can I??? I just really want to get some nitrogen fixer in there ASAP. im itching to get going for the fall planting season. cant wait!! thanks in advance for your help.

All root crops are treated as annuals. Or you have to dig some out and leave the others it is a bit tedious.

You don't need to dig them out exactly at 4 months - it depends on whether you want them to be smaller or more football sized. I'm in Atlanta, and tend to leave them until the nights start dropping below 40. You just need to dig them out before the first frost, but I find they're sweeter with a bit of cold.

I just leave a few in the ground. They are marginally perennial where I live. Those left in the ground may or may not come back the next year.

Sweet potatoes are native to a climate where there is a moderate rainy season and a dry season.....the vines grow out during the rainy season and the tubers are the plant's method of surviving through the dry season. So many people in milder climates still have trouble with sweet potatoes as a true perennial because the cooler season, with an occasional frost to kill the vines, is still wet enough to then rot the roots. Soil may make a difference.....so that in a place like lower GA or FL they may survive much better in a free-draining sand than in a soggy clay.
In a heavy monsoon climate, another problem takes place....the vines may grow year-round, but the roots will rot in the wet of the heavy rains. So if you want to harvest roots in such a climate, they need to be dug before the heavy rains and floods and stored in the dry. In such a climate (Bangladesh is the one in my experience), sweet potatoes are grown as much for the greens as for the roots, and as a green, they are available throughout the year.
Another thing to bear in mind is that, unlike white potatoes, the sweet potato root is truly perennial, and in an amenable climate where it doesn't rot, it will increase in size from year to year. I have read of 50 pounders! But roots over a year old will become more fibrous, tough, and pithy. So, if you are interested in high yields of edible roots....this is one reason to try to harvest most of them yearly if you want good eating quality, and then propagating from root shoots or vine cuttings the next year.

That's helpful to know about their natural cycle, Alder. Maybe they could be planted on mounds so the tubers are kept a little drier during the cool season, so they don't rot. But in Zone 9, they may only go dormant if not irrigated, thinking it is the dry season.

I harvested some of the greens today and I harvested a whole ton of them. One question I have is " when you harvest the greens do you harvest just the leaves and cook that or do you harvest the whole damn vine straight down to the stinkin' earth???" Kirsten, I'm taking your advice my friend!!! I'm gonna leave them in till the overnight low temps hit 40!! Right now the overnight low is at 88 or 90 or so YIKES! but I'm gonna be mad at ya if I don't have MY sweet potatoes I grew on my table at thanksgiving!! Anybody know of a site that would show me what kind of historical temps there have been in the PHX of the AZ leading up to turkey daaaay! Yummmmy sweet potatoes bring em to me!! I got the big flats lager beer from Rochester, ny going on right now. I'm on my third one and it's almost the cheapest beer on the planet$3.00 6 pack tjoes has a simple times 6 pack for $2.49 but I don't like it.

Oh and for everybody that was telling me that I could put beans in before I harvested my SP well I got a picture for you hahaha damn I had a bumper crop of SP this year. It just grew and grew and grew.

When I harvest the greens I just pinch off the growing tips of the vines. This also helps keep the vines a little more compact, because the plant will generally put out another branch when you pinch it. I put the tips in salads, but you could also cook them.

Generally I simply let them grow until frost, or until consistent cool weather stops the vines from growing. The roots don't like temps below 50-55 or so, but the soil retains warmth for quite a while. You can feel around in the mulch and grab a few early, but they will be sweeter, larger, and more of them the longer they can grow in any normal, temperate, relatively short season climate. If I had just a few plants and could give them plenty of time and attention, I'd be tempted to feel around for a few large roots around now, since these may start to overgrow...get pithy, sprout, get bad spots, etc. and getting them out of there would direct energy to the smaller ones for the rest of the time. But that's hypothetical on my part. I just notice often that the very largest ones at harvest time are less than the best eating quality. But the overall yield of good ones is usually significantly more the longer and warmer the fall season is.

Andrew, here's link to the US Climate data for the Phoenix area. Click on the "Day" tab and it will give the normal values by month. Looks like the night time 50s are in October and into November.

http://www.usclimatedata.com/climate/phoenix/arizona/united-states/usaz0166

Anyone can use the link to find the temps for their area. You just have to enter you location up at the top and it will take you to the values for your area.