What's in season? The sweet potato question.

I don't know about you, but I am never 100% sure about what is actually in season or not. I went to the Headhouse farmers market Sunday and saw so many good things & thought I had a handle on what is in season locally & got so excited. Then I saw the sweet potatoes. I forget who had them, but there they were. And since I was planning on making beet & turnip chips for lunch this week, I thought - "hey! sweet potatoes - lets make some of them into chips! And make some sweet potato fries for our Monday night veggie burger dinner!" And so we bought them. And then I wondered - "hey! potatoes aren't in season till the fall! Isn't that the same for sweet potatoes?" According to this site they are not in season until fall. But here is what is in season - in the Northeast now. I have included spring and summer because we are pretty much in between both right now & I know how confused I get.

Spring:
Vegetables
asparagus
beets
broccoli
cabbage
cauliflower
fiddleheads
garlic greens
greens
arugula
beet
bok choy
chard
collard
cress
dandelion
mizuna
mustard greens
sorrel
turnip
lettuce
mushrooms
parsnips
peas-snap and snow
radishes
rhubarb
spinach
sprouts
Fruits
apples
strawberries
Seasonings
chives
cilantro
dill
marjoram
mint
oregano
parsley
sage
thyme
Summer:
Vegetables
beets
broccoli
cabbage
carrots
cauliflower
celery
cucumbers
eggplant
endive
fennel
garlic
green beans
kohlrabi
lettuce
mushrooms
okra
onions - red and yellow
peppers - hot and sweet
potatoes - new
radicchio
scallions
sprouts
summer squash
sweet corn
tomatoes
Fruit
apricots
blackberries
blueberries
cherries
currants
elderberries
gooseberries
melons
nectarines
peaches
plums
raspberries
Seasonings
basil
cilantro
dill
marjoram
mint
parsley
rosemary
savory
tarragon