You know foliage colour is difficult to predict but you also have to look at where you want to go too. Fall colour starts in the north (as it turns cooler there first).
I'd pick Oct 11th to 25th and keep my fingers crossed!

It depends on where in New England you are going. Foliage season in the Boston area occurs the end of October. The last week of October usually has great color. The further north you go, the earlier the foliage starts.

hi gordon. i'd say before london. here's a link to pages for each state. http://ncnatural.com/fall-color/fclinks.html
where do you plan to go? what else are you interested in seeing?

If you plan on flying in and out of Boston, then I would pick October. September may still be hot. I think Oct temps are very nice in New England. I vote for after the London trip. I would plan to rent a car and drive Vermont or New Hampshire or both. Beautiful lakes in NH surrounded by trees. Vermont has the beautiful inns. I love that time of year.

But if temperature is more important, go with the earlier date. You can expect temperatures in the 40's in late october, but probably not freezing cold yet.

There is a mismatch between wanting 50+ temperatures and wanting to see the colors -- the colder weather brings on the colors. So you may have to compromise on that.

I'd say the second week, after October 11. That is usually the time for fine foliage in southern Vermont, only about two hours west of Boston. While daytime temperatures may be quite comfortable, however, it will surely drop below 50 at night.

I'd go earlier. If foliage is important you can go north to the Burlington VT area. Temps in late September will still be quite warm, there's no guarantee in October.

I'd go earlier. As someone mentions above, foliage is all about temperatures falling... so you may not be able to combine the two (but you could get lucky). Just be ready to drive further north, perhaps.

Since both of your chosen time periods might miss the foliage in most areas....I'd go from Sept 5 to 20. Consistently the best weather of the year, yet the crowds are gone and most places (lobster shacks, homemade ice cream huts etc) are still open.

I'm going to vote with Tracey2cents. Two years ago we had torrential rains and flooding on Columbus Day weekend. Some weeks during foliage season are crummy. You could visit Camden ME area the third weekend in Sept, enjoy lobster shacks, visit the Common Ground Fair (if you like organic living) then head over to NH for some early color but as Tracey says, early Sept can have some fabulous weather. It might as well still be summer without the crowds although weekends in some areas are always busy. I've seen half decent foliage as late as Oct 23 in Rhode Island but there will be little left in northern New England esp the White Mountains. I think your choice of dates depends on what else you'd like to do besides look at leaves. We usually do a get away weekend the third weekend in Sept and even that early in Stowe VT there was no color yet. A good cold night can bring color out. I always feel like peak in the Concord NH area is Columbus Day weekend and have seen some great color in Mass as well. Good luck choosing!

Another way to enjoy fall foliage... Several years ago, my husband and I did a Bike Vermont bike trip in southern Vermont during the Columbus Day weekend.
The foliage was spectacular. You stay at an inn and breakfast and dinner were included. The inn was charming and the food was fine dining level. You can cycle as much or as little as you want. I highly recommend this if you are an active person.

Thanks to all for the valuable advice. I'm inclining slightly towards the Oct 11-25 option as we will probably concentrate on the southern part of New England. Low night-time temperatures are no problem, I just wanted to gauge whether it would be unpleasantly cold during the day time, which seems unlikely unless we are unlucky.
We've travelled extensively in the US in the past (CA, NV, AZ, WA, DC, MD, VA, NC, SC, GA, FL) but have never ventured up to the New England states before.
Once I've made my final decision on dates, and booked my flights, I will start thinking about an itinerary - I've heard it said that New England is ideal for a road trip, which suits me well as we love driving in the US. Hopefully I can get your good advice on this aspect too. Thanks again.

Hi Gordon,

Yes, New England is great for a road trip especially in the autumn but do book your accommodation in advance as it gets very busy. Some places have minimum stays of 2 or 3 nights so you might need to consider that too.

I can't recommend any specific places as we usually take leaf peeping daytrips from our home in Massachusetts.