How To Nail The Perfect Measurements On Your Garden Arch Trellis

Garden arch trellises have long been popular. They can be decorative, providing somewhere for those climbing plants you should grow. They can be practical — a DIY garden trellis for your vegetables, for example. The challenge can be working out dimensions that look good and provide adequate support. Too wide, and the center might collapse under the weight of growth. Too tall, and there's a danger it might topple. I'm House Digest's expert carpenter, and I'm also a keen gardener. I'm going to give you some ideas for how to nail the perfect measurements for your garden arch trellis.

Often, you will be guided by one dimension, either height or width, that you already know. For example, you may want it to span a path or complement an existing pergola. There are no "standards" as such, but I generally go with the width being around two-thirds of the height.

So, if a small trellis arch for flowers or vegetables was 4 feet wide to fit in a particular bed, I'd probably go with a 6-foot height. For something to walk under, you'd probably want a clearance of 8 feet, so I'd use a width of 5 feet or so to provide good support. For a truly dramatic garden arch trellis that's 10 feet high, I'd suggest a width of 6 or 7 feet. Before I commit, I also like to do a quick sketch, using inches instead of feet, to check the visual balance.

Whenever possible, I like to repurpose existing items as DIY plant trellises. However, while these are perfectly functional, they might not meet your aesthetic requirements. With a small garden arch trellis made of wire netting, to train vegetables, for example, it's easy to experiment. I would just set it up and push on the top with my hand to judge the amount of support it gave. With larger wooden structures, this isn't practical.

One principle employed by some garden designers is to use what's called the golden ratio. It's a mathematical device that has been around for at least a couple of thousand years! This rule says that the height should be 1.618 times the width. So, using that factor, a 6-foot-wide trellis arch should be 9.708 feet tall — let's call it 9 feet 9 inches. That's not far off the roughly two-thirds proportions I suggested before. Whatever materials you use, and whether you choose a domed or flat-topped arch, this basic calculation seems to work well.

Okay, I've dealt with width and height, but not depth. Once again, there are no hard and fast rules, but a third to half the width works in many cases. That said, visual appeal is important, and you might want a whole long tunnel. It will also depend on whether the arch is self-supporting, in which case it would need a wide, stable base, or be concreted into the ground. This is one measurement I'll leave you to nail yourself.