It all depends on how the arbor is made. My came in 3 sections: The top piece and two side pieces. The posts had to each be dug down 2 1/2 feet and set carefully with a level. Then the top piece went on which had to meet the side posts exactly, and measurments were important. It was a big wooden arbor. Smaller arbors are usually put together first, then the holes are dug at the proper determined spacing and depth. It also helps to put gravel under the posts for drainage if you're installing a wooden arbor, especially.
If the arbor is a very heavy one, you will need a few guys to help. My husband and son put this arbor up. It was a big job due to it's size.

Here is a link that might be useful:

Hi Suzy,

My arbor is not a very heavy or expensive one. It came in pieces that were very easily put together. [Your arbor is gorgeous by the way :-)] The problem I have is that the sides don't have posts that can be dug into the ground. It has horizontal wood pieces that evidently allow it to sit 'on top' of a surface. Very strange. How it can sit on top of a surface when a light wind blows it over is beyond me.

So I want to take the bottom horizontal piece off and install it into the ground, but am not sure what is the best way to do that. I was hoping someone who was handy might be able to help me figure that out.

:-)

Can you just bury it a little deeper so that the horizontal piece is below ground? I built one from 2x4's and wondered afterward if the whole thing would have been better with cross members at the bottom which would have been buried. Mine is too big 48x40x9' and heavy to blow over and sort of crude, but will eventually be covered up by two Betty Corning clematis and two climbing Westerland roses. At least it was cheap.

Hi Harry,

Thanks for the input. I suppose I could buy the horizontals, but I would have to dig them down a foot or so for them to have any effect. I would lose a foot of the trellis and then the panels would be underground too, so I don't think that will work for me.

Your trellis sounds nice. I like rustic. I also like the size of it. 9 feet sounds just about right.

thanks.. :-)
ann

I've been looking for a simple arbor myself and several of the ones I've seen have four stakes that are driven into the ground like big tent pegs. These are then nailed to the structure at the bottom where plantings would no doubt cover them in no time.