You're not gonna want to hear this but you've got enough trees for that size garden........in fact, quite a few MORE than enough!

I know it's hard to imagine those little babies growing up to full size any time soon but it will happen and sooner than you think. And at some point you're going to need to think about removing a few, forget about adding more.

White pines (2) -- 50-80 tall (or taller) with a 30-50' spread each.
Tulip trees (2) -- 60-90' tall and a 30-50' spread
White Oak - 60-80' tall with an equal spread

Just with these 5 trees, at their mature size you have easily exceeded the available canopy space in your garden by a significant factor, not to mention the other various trees you already have growing. What happens when you have that dense a planting is the trees struggle for light and nutrients, diseases and insect problems are more frequent and more pronounced and your entire garden will be heavily shaded all summer. Any other smaller plants you may wish to grow are severely limited by shade, tree roots and lack of water.

This is a perfect situation for some onsite design consultation help to assist you in winnowing down your selection and perhaps relocating a couple of trees to provide whatever privacy screening, shade or aesthetic result you are seeking. Right now you are looking at a bit of disaster down the road.

Ditto. Don't plant any more trees.

Thanks for the comments and advice I appreciate it. I will be looking into making some changes when it warms up a bit.

Thanks again!

I have a very similar backyard with many houses visible, except the people who lived here planted many trees around 10 years ago. Now they are from 20 to 35 feet high and I'm very glad to have them.

Ideally when your trees start to get to around 15-20 feet you will start trimming them to keep them to a manageable size. If that's not something you want to do/have done or gets to be too much work you can start taking them out. Try to keep trees from growing into the neighbors yard, they will be be easier to manage.

I would say keep on planting trees, but think about grouping them into clusters, you can plant them quite close to each other (5-6 feet no problem). They will grow together and any imperfections, pruning, or tree removals won't be so noticeable. Probably you could come up with a very nice plan for tree areas, lawn, walking corridors etc.

I agree you will need some more conifers to break up the view of the houses. You don't need a wall of green, just something closer to look at in winter. And I would consider small trees close to the house/deck, I love the feeling of being surrounded by leaves. And don't be in a hurry to cut off low branches if you like them.

It sounds like you are very comfortable picking out trees and trying things out so I think you will do well if you decide to have a tree filled yard. Here in the plains of Colorado it's impossible to have too much shade in summer, and even with 13 trees in my 55'x55' back yard (and a row of houses to the south and my house to the west) there is good grass, plenty of flowers, getting a few roots but no problem. (If you count multiple trunks in a clump of aspens/cottonwoods, I have 22 trees in the backyard, all are between 9 and ~40 feet tall and 1.25" and 10.5" diameter, most of them towards the taller end of that range.)

Really, I think many thin trees are much better than two or three huge trees. You can find some info about keeping trees small if you look.

You can find some information about trimming trees to keep them small if you look.

Here is a link that might be useful: pruning to keep trees small

Holy Toledo! You have 12 trees in a 60x60 yard and are thinking of planting more!!!??? Did you say that at least one is an oak? One full-grown oak tree can overpower a 60x60 yard.

If you want evergreens for screening purposes, you should get rid of some trees you already have. Or, I agree that they should be re-arranged in special groupings, not lined up like soldiers.

Pruning any tree to keep it significantly smaller than it naturally wants to be is NOT a recommended practice........ask any arborist. It can create structural issues, generate rapid and improper growth and typically compromise the health and shorten the life of the tree.

What the OP wants to be considering at this point is the selective culling of the collection and looking at better placement of the retained trees to provide the desired aesthetic. Any other advice is irresponsible.

So many of the trees you planted are giants, but almost all of them have dwarf versions that would fit nicely into your yard. For example, you could replace the Picea pungens 'Hoopsi' with Picea pungens 'Sester's Dwarf'. Looks nearly identical, just smaller and slightly more of a steel/silver blue than bright blue.

The weeping pine is a good choice, but the 2 white pines are not intended for a 60x60 yard, plus there is really nothing special about them in my mine. Pinus strobus (white pine) has tons of dwarf varieties that are stunning. I would select your favorite and remove the white pine (species).

Tulip trees are enormous! Even a dwarf like Liriodendron tulipiferia 'Little Volunteer' is a large tree, but you could consider planting one.

Ash tree needs to go, is the Gingko species or a cultivar? Is the Dwarf catalpa a special or cultivar? magnolia, if not dwarf needs to go, plenty of dwarfs to pick from.

Try and sell them on craigslist to recoupe some of your cost...consider it a learning lesson and move on... the trees you have now will literally swallow up your yard in 5-10 years.. and I can assure you that taking down overgrown trees costs far more than removing them in advance.

If you decided to do this, please post back. Many here or on the other conifer and tree forums can help you select appropriate cultivars for your yard.. Just because it's a small space, doesn't mean you can't enjoy 12 trees, they just need to be dwarf versions.