Where can I find out how deep to plant bulbs in zone 7?

I'm zone 7 and I use a trusty bulb setter that digs out a hole at the appropriate width and depth required for each bulb, but if you don't have one or can't get one then dig twice as deep as the bulb is long. Also, a couple little helpful hints when planting bulbs. A little bone meal in the bottom of the hole is very much appreciated by the bulbs and it wouldn't hurt to bury a sheet of chicken wire just under the soil to keep the squirrels from digging them up. You can wrap each bulb individually, however, unless you have burrowing critters that love to eat bulbs, then laying some just under the soil will suffice.

Good Luck and happy planting

The general rule for planting seeds is to plant no more than two times the diameter of the seed. A bulb is not a seed, but a modified stem or root structure. Bulbs, regardless of where you live, should be planted two to three times as deep as the size of the bulb. This depth would be measured from the soil surface to the bottom of the bulb. Also, don't forget to add some compost and fertilizer before you plant your bulbs. Here is a great guide that should help you with bulb planting and care.

http://www.urbanext.uiuc.edu/bulbs/planting.html

Rule of thumb is to dig a hole twice as deep as the bulb is high. If you get frost heaves in your area, go a little deeper. When I planted lilies (not daylilies), I put about an inch of coarse sand at the bottom of the hole to keep the bulb drier in winter.

No matter where you are, always plant your bulbs 1.5 times the height of the bulb.