I realized I didn't address the garden issue you have. Ha. I'm dumb sometimes.

It's going to depend on what you have in mind and what capabilities you have to install the equipment, as well as what you're currently using.

I'll discuss two situations, in the first, you have a preferred vendor for all of your wifi stuff. Someone like ubiquiti. From there you have two choices, either find an outdoor unit to install on the side of your home near the garden(something with waterproofing), and install an indoor unit as close to the garden as possible. In either case it may be a good idea to get a directional or semi-directional unit that can "point" the wireless in the desired direction. It doesn't need to be a very directional unit (like a dish antenna), and something like that may actually not improve things very much. So look for something like a panel antenna style unit. It may be a good idea to get a point to point panel-like semi directional unit. If you're uncertain what I mean, Google panel antenna and it should be a bit more clear. If no such type of device exists, I would see if there's a unit that can use external antennas and go that way, buying a compatible panel antenna for the job.

If the garden is not very large, you may be able to get by with a normal "Omni directional" unit.

Installing outside has the difficulty of getting it wired into the network. The most common solution is to run a cable through the soffit, into the attic, and to the rest of the network. I would highly recommend outdoor cable that is UV rated, otherwise it will fall over time. Failure will take many years with a non-outdoor rated cable, but it will happen. So a bit of extra investment in cabling is going to be worth it in the long run. Nobody wants to climb through the attic to run ethernet, and nobody wants to do it twice for the same network run. So save the time and effort of doing it, and get the UV rated cable.

The other scenario is that you have random network gear or no preferred vendor. In this case the network will be disjointed, where you have to disconnect from your home wifi, and connect to your garden wifi, either manually or from saved profiles automatically. This is a bit less ideal, but usually cheaper. Finding a wireless bridge access point for outdoor install, or simply putting an access point as close to the garden inside the home, may be sufficient.

I'm planning on doing the same, but it's winter right now, where I am, so I'm at a stand still. The network in question is ubiquiti based, so I got a U6-Mesh, which I'm planning to install in the soffit (the unit is water resistant and has a "ceiling mount" option which will embed it into the soffit part way). The biggest challenge I have is getting the wire out there. In that case the wire will not be outside, so I don't need UV resistant cable, but I'll likely get it anyways for that unit. I'll skip the specifics of my difficulty running this network cable. While the unit is called the U6-MESH, it does not need to be running in a mesh operational mode, which I will not be running it in a mesh mode. The U6-MESH is small, its a bit larger than a redbull can, so I shouldn't have any issue putting it in. It's omnidirectional, so I'm planning to place it around the midpoint of my home, in the soffit, to give fair and adequate converage of the area. I want to repeat this for the front of my home.

The last step for me, and something I would recommend, is to have someone with a WiFi device that can report signal strength, at the very end of the area (at the back fence) about as far as possible from the access point as anyone should reasonably be for access, then "turn down" the broadcast power of the unit until that area is just barely covered enough to stay connected. Outdoor wireless can go far with no obstacles in the way, so I want to limit coverage so I'm not blasting my neighbors with the power of the unit at full, all day and all night, possibly disrupting their wireless in the process. My main motivator for this is that if they can "hear" my network, they can connect, and if they can connect, then it's possible for them to illegitimately use my internet, or "hack" into access that they have not been given. By limiting the signal strength, I can reduce this attack vector. As long as the signal can be picked up outside, however, it will never be eliminated. The point is to make it harder for the layperson or casual hacker to try. Any professional trying to gain access will overcome this with ease, so I don't want to invest too much effort into it.

I hope that helps. I have no idea if it will. Either way, good luck.