Does your garden get lots of full sun? Not getting enough light will reduce yields. What varieties have you planted?
You are quite far north. How long is your season? Are you planting varieties that will mature in your season? I have found that here in Northern UT at 5000 feet elevation, 75 day corn takes 95 days to mature because it is cooler on average than the area where the corn was developed. Try planting some varieties that mature earlier. All of the early varieties like carrot, radish, peas, lettuce, kale, cabbage, turnip, kohlrabi, should get mature for you. Get the earliest tomato you can find. Bush beans would be a good choice too. They come on quick.
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-