I am going to plant cilantro this year and I am not sure if it will come back every year. I know a lot of herbs do, but I have never planted cilantro or parsley. I have looked for a answer to this question and I can't seem to find a plane and simple answer. I live in Idaho so we don't get really cold or hot weather but it can be very unpredictable. I always start my herbs in containers, and then I replant them in the garden. So does any one know if they are perennials?
Coriander is an annual. The leaves are commonly called cilantro. It belongs to the Apiaceae family of plants (once called Umbelliferae from the shape of the flowering 'umbels'). Members include a number of herbs and vegetables such as parsley, dill, caraway, carrot, parsnip and celery. Some of the members are annuals, some biennials and others perennial.
Cilantro bolts quickly in hot weather but the increasing day length also plays a part. If you can find seeds, 'slow bolt' cilantro's supposed to take longer before bolting but I've never tried it.
To get the most from your cilantro, start early. You can also pinch off flower heads as they just begin to show. But as weather heats up, it'll make more and more buds and less leaves. Start new plants then. Another trick is to plant after the hot days of August have passed. The plants grown will let into spring if the winter isn't too cold to freeze them.
It's an annual plant - however, if you let it go to seed after it flowers, it will seed itself in the surrounding area, so hopefully, you'll always have one or two (or maybe several) plants ongoing, so long as it doesn't get too cold where you are - I note that Idaho ranges from USDA zone 3 up to 7b. More information here http://homeguides.sfgate.com/cilantro-perennial-herb-67386.html
I know Idaho well. Mostly Zone 3. No, cilantro and parsley are not perennials in your zone. They are annuals that make lots of seed for reproduction in the spring. I wouldn't use this seed for replanting. I buy ALL of my vegetable seeds from Territorial, which is close to you as well...ALL seed packets should be LABELED NON GMO. Using your own seed is not smart. Your plants are fertilized not only by your own plants but by farmers nearby in the Palouse growing similar plants and the pollen floats on the air. No way to know what your seeds will produce genetically.
The soil in Idaho can be difficult. Raised beds via double digging (4' of fluffed up soil will become 1 foot). Decomposed organic matter is the ONLY way to improve any soil...ANY SOIL. Dig trenches at the bottom of these beds. Get a soil test so that you know the pH...all plants do best at different pH's and the available chemistry that plants have to have to photosynthesize to make their own food.
You have an incredible Cooperative Extension Service through Washington State University. Cheap soil tests, tons of CORRECT information and they are aware of the same zone, soils...make use of them! I've gone through their master gardener program three times. Worth every bit of time...and it is almost free!