bibbo: if you want mature potatoes at their maximum size, wait until the tops die away. If you want immature "new" potatoes, just scrabble the soil away from the side of a hill to see whether they are ready. Some people take a few young potatoes off every plant and then leave the rest in the ground to mature. In my opinion, though, fully mature organic potatoes taste as good as immature ones. Regards, Peter.

Potatoes planted in soil make it difficult to remove "new" potatoes because you have to disturb the soil too much to get them. When the plants blossom indicates the these "new" potatoes have developed and when the above ground plants whither its the time to harvest.
The only reason why your potatoes might produce any toxins at all is if you expose them to sunlight and they get those green areas that I forget right off what that is called.

fro idaho potato web site

Is there any validity to the notion that the growths that form on potatoes after they have been sitting for quite some time is poisonous, and at the same time is also true that if the potato is green it also has poisonous compounds?
The sprouts that form after a potato sits for a while are not poisonous, its just the potato trying to replant itself.� If they are small and can be rubbed off by hand then the potato is fine.� If they go into the interior of the potato, they are fibrous and so won�t taste very good so I�d toss the potato and buy fresh ones.� The greening happens in nature when the potato is exposed to the sun and in storage or when on display at the store when exposed to light.� This tastes bitter but is not poisonous, so trim off before baking or boiling and prepare as usual.

Great thanks I am going to wait till june to see how much farther they grow and if they start to flower.

thanks again

the green that develops when potatoes are exposed to light is solanine. This IS toxic. greening can be avoided by hilling up sol around the base of the plant, to prevent exposure to light.

Where I am the older the potatoes get the scabier they get but I eat them regardless. I start eating them when they get big enugh to eat and keep at it until the fall. Then I dig up everything I didn't eat yet and store them and eat them over the winter. By spring they are looking kind of sketchy and are sprouting so I plant out again. Point being, you can do whatever you want.

Some years ago, a girl from the Cape Verde Isles planted some potato peels in my garden and to my surprise I got a small crop of potatoes. I have now done the same in a grow-bag and have some healthy green tops. When you talk about building up soil around the potato, do you mean around the green tops? And is it the green tops that shouldn't get sun?

handsy,
You never want to cover the green tops. This covering with dirt is talking about moving up dirt around the green stems below the leaves. A few small lower leaves may get covered, but that is ok.

handsy, what you don't want exposed to the sun is the immature potato. Lots of people "hill" them (add soil around the lower area of the green plant) in order to keep the newly forming potatoes from pushing out of the soil. You can also add mulch, anything that will cover any new potato growth.

help. i have garden going .i live in south florida.next to the potoe i have oions and green beans and corn and all.....but i do not know when to pull them out....my ground is like sand.but i had dug down and planted the russet potoe in jan.this year.now as i keep track of it....it looks like green flowers growing .they look like they are 5 inches tall and wide.all green leaves.i keep putting down fresh soil from miraclegrow dirt.i have never done these before.how do i know when they are ready.they are in sun light as well......i planted them in jan.2011 .i got the starter potoe from walmart. help me if you can...how many months does it take and how do you know when to pull them out.......thanks.help.

rox, they will die down when the fruit/potatoes are ready.
You can plant them in trash cans next year if you like & dump them out when the vines die/ NO digging, just pick up the taters. If you are going to save taters for Fall/ Spring planting (seed potatoes), then let the vines die completely down, the remove them.The following day dig your potatoes. This will help to keep early or late blight from spreading from the vines to the seed potatoes.
The post by peter & wayne 5 are true.
As for green skin on potatoes.
Peterson Field Guides/ Venomous Animals & Poisonous Plants says on page 86 "While the tubers are edible, all green parts of the plant, which contain the concentrations of the alkaloid solanine(including the green skin of some potatoes), are potentially toxic. Sprouted or green-skinned potatoes have caused most reported poisoning cases.
potato: solanum tuberosum L. Nightshade Family.
But do not believe me. Do a search for your self!