Young couple, both still living at home, are getting married next month. They have bought a fixer-upped house and both love gardening I know nothing about gardening but would love to get them something nice/useful ($150- 250 range).
If they have any outside living area how about a gift certificate to a local outside patio furniture type place?? I wouldn’t pick it out for them though. They can relax and enjoy the view of their gardening labor!
Other ideas but I would want to know if they want these things:
Rain barrel
Garden bench
Adirondack chairs
We’ve bought gold trees as gifts in the past. Depends on your climate
A raised planter box that self waters is nice also.
Are they registered somewhere? Do they want a gardening gift? In that price range, I’d want to be sure what I bought for them is what they want.
@FlyMeToTheMoon They are registered at Target and for much less expensive stuff. All the gardening things has been purchased. I’ll talk to the MOB, but was hoping to go into the conversation with several ideas and ask which ones the couple would want.
I know gift cards sound lame but with a fixer upper and a penchant for gardening a Home Depot or Lowe’s gift card would fit the bill. At one wedding I went to that was all that was asked for.
I would get them a gift certificate to a local nursery. As a gardener, I would be thrilled with this. They could buy supplies, flowers or trees. Bliss
I think a gift certificate to a local nursery would be great, or you could try these site, well loved by gardeners:
https://www.gardeners.com/
Based in VT, with a great selection of self watering planters and tomato supports
https://www.plantdelights.com/
Based in NC, one of the best plant suppliers, with unusual plants for every zone.
https://www.groworganic.com/
Based in CA, has a lot of everything
There are a lot more out there!
A Mantis tiller.
A sturdy plastic wheelbarrow. A “bouquet” of larger garden tools (shovels, pitchfork, rakes, etc.) tied together with a ribbon a la a bouquet. 
These are practical gifts any gardener can use. But I see they already have some tools.
Wheelbarrow isn’t a bad idea - they can get expensive, so it would be a nice gift. A True Temper poly would be great.
One thing I can not live without in my garden is a DeWit dutch hand hoe. (They come in left and right hand. You can’t go wrong with one of these - even if they have one already, they will love having another. But it’s doubtful that they have one because you don’t really see them around anymore.)
A vintage/antique galvanized watering can is always nice. I received one as a wedding shower gift. Loved it.
Taylor’s Master Guide to Gardening was another shower gift I received that I absolutely loved.
Beyond that, definitely a gift certificate to a local nursery, but ask around a little to figure out which, if any, nurseries the real die-hard gardeners like to visit. Quality, selection and price matter. Are there Agways in your area? A gift certificate to an Agway with a nursery would be great, because they could use it on tools, plants, seed, feed … whatever they want or need.
A gazing ball, or pyramid trellis, or sundial would also be very nice.
If you want to do a gift certificate for online stores, I would agree with Gardener’s Supply Company. Can be a bit pricey, but it would be hard for them not to be able to find something they want or need there.
Honestly, I think I would stay away from the Home Depot/Lowes card. They will be tempted to use it on building supplies or something. If that’s what you’d want for them, that’s fine, but they might enjoy having a gift card they can only use on gardening-related items. That might feel like more of a treat, especially if they can splurge on plants or something expensive that they wouldn’t otherwise have the budget for.
A nice squirrel-proof bird feeder might also be appreciated.
If they have bats - a sturdy bat house. If there are hummers who like to visit their garden - a couple of hummingbird feeders.
Best bat house:
https://www.amazon.com/Looker-Products-Approved-Organization-Conservation/dp/B000FLTO6A
Great hummer feeder:
https://www.amazon.com/More-Birds-Hummingbird-Stations-14-Ounce/dp/B007G2P0FA
Bird bath or fountain. A St. Francis statue.
How about:
A beehive
Beekeeping Kit
One of a kind composter from mudpiegallery.com
A cedar potting bench
A vertical / wall garden
A flower press (to preserve their garden blooms!)
Custom made bird house / bird bath
Botanic Garden membership
What a wonderful idea! Probably the most practical would be a gift card to a local greenhouse/landscape business. That way they could choose a shrub, perennials, annuals or even dirt /mulch if needed!
I love the suggestion of #9. A wheelbarrow with gardening supplies and a few annuals or perennials could be so sweet.
The only thing I would caution you about would be statues or benches that might be too taste specific.
I would like to have another wedding shower and only receive ALL these wonderful garden gifts!!!
Me too! Mr. says we can always use another bat house 
I agree with the advice to avoid statuary and benches, and would add bird bath to that caution. Very taste specific.
A pyramid trellis or obelisk, while somewhat taste specific, is generally pretty generic and not terribly sylized. Plus, they get covered in vines, and you can always use more than one. (I’d love just one, and I’ve been gardening for 20 years!)