APHIDS!

what's going on??? how do aphids multiply so well with lows in the 50s? my collard greens are covered and they've recently discovered the brocolli too. sprayed them good today with a soap/neem solution. if they're still abounding tomorrow, i'll give the collards a good pruning, throw away most of the aphid population and spray the rest again. but we've been heavily depending on collards for our veggies recently. just may have to (gulp) BUY some!