I'm not sure it was the best way to approach you about it, but being that you don't live there the neighbor might have thought it was easier to get a hold of you with a letter.

I don't think it was meant to try to get money out of you necessarily, but rather hey I'm doing this and if you're interested in getting it landscaped at the same time it might be beneficial to both of you. Probably thinking since you did all this other stuff that you might be interested in doing it. It is also possible they want to improve that part and since the other side will not look as nice when done and likely detract in their mind that it was worth asking. You don't ask you won't receive. Plus I can see from the layout why they would want to purchase that piece. It would make more sense from the shape.

I would stifle my first, second and third reactions ...

Then I would say, thanks but no thanks, because after paying for the fence and the retaining wall, your budget for landscaping is exhausted for the foreseeable future.

Welllll, I would say "sure! if you split with us the cost of the fence and retaining wall."

It's not obnoxious or pushy. It's not like he's building a fence or retaining wall along the property line without ever having had contact with the neighbor. (That does seem to be what you did, based on your reporting. YOU are looking like the neighbor who's gonna be a pain! I'm sure you aren't and this is just a misunderstanding...)

Did you talk to him at all before doing the retaining wall and fence?
Maybe he's trying to gently remind you that neighbors like to be a part
of these decisions, even if it isn't legally required. It is unfair of
you to complain about the benefit you have given him for 'free" when you
didn't give him the opportunity to offer an opinion or pay half or...anything.

...

Can't tell from your image but I suspect that his request might be as innocent and sensible as thinking that a cohesive plan that covered the entire hill would look better for everyone and he wants to know if you're up to it. It's just neighborly.

Sort of like how I'm thinking of asking my nextdoor neighbor if he wants to go in on a shared treatment of our parkway/hellstrip. It would probably look better if we ripped out his half dead juniper hedge and my selection of weeds and planted something unified across the entire space.

From the map you shared, it looks like a cohesive landscape design would benefit both properties. Have they done a good job with their exisisting landscaping?

I would meet the neighbors and discuss the landscaping plan they have in mind. Take the time to think about the ideas and then decide if it's a good idea. Good luck!

A good landscape designer can figure out a plan for his property that is aesthetically pleasing without putting one single plant on your property. That being said, it probably would look better if the landscaping crossed over onto your property and would enhance both properties, so I can see where he's coming from - innocent enough request. He cannot force you into this, nor can he landscape your property without your permission, so if you don't want to do it, just say no. I suggest having a conversation with him and let him know it's not feasible right now due to all the improvements you've already made (i.e. finances) but perhaps down the road (if this is something you're interested in - if not just politely decline). I take the view most people are relatively reasonable if you take the time to talk with them and explain things so I would go that route.

Level headed approach is a good idea, since you'll be neighbors. I vote for the polite decline, "maybe we can revisit at a later date". You don't know these people at all. They could be making an "innocent request", they could be looking at your renovations and thinking "ca-ching!!" and all things in between.

Get to know them, first. If it seems like a situation where you could both work together- I stress together- and it makes sense, sure. Take a peek at it.

fori says

Maybe he's trying to gently remind you that neighbors like to be a part
of these decisions,

That's a big fat bag of "no", unless there is a clear codicil for neighborhood review. Period. As long as it's on the OP's property, it isn't up for debate. I have a saying- as soon as you get the stones to invest a lot of time, effort and money in MY property, you get input. Until then, sit back and watch beauty unfold. Renovations are not, in fact, a group decision.

Why, just now, does this proposal come? As in, why has this never happened before? Hmm...

Four of the households that abut my suburban property contain individuals that think they are entitled to reach or walk onto my lot and cut, spray or pull out plant material, without prior discussion. This includes a bamboo hedge, whose screening presence one would think would have been seen as being to their benefit (instead the conclusion reached was "It drops leaves on our bark mulch!"), potted azaleas that got hit by careless application of herbicide, a climbing rose that was on my side of the shared fence being deliberately sprayed with (and ruined by) herbicide, and so on.

Just reviewing the history now makes me want to sell out and move.

So if you got a polite letter suggesting sharing a project, you have no problem.

I probably would have had a similar emotional reaction to being asked to share expenses of yet another project. Your outrage / irritation is understandable.

But when I re-read what you said was in the letter, I can see a different side. He has an odd property on a hillside where you also share a section (the bottom of the hill?). You don't live there yet so he probably doesn't know how to reach you other than by mail. Maybe he was inspired by all of the work on your property so far and he has decided to landscape his hillside. Judging by your drawing it looks like your strange sliver directly relates to his property and your landscaping focus has been on the square section not the sliver. He is asking if you would like to go in together on a cohesive landscape that would make his odd lot and your sliver work well together. And if you are not interested in that option, he is wondering if you would consider selling him the sliver to make the lot more cohesive.

All of that said, I would reach out to him and have a conversation. Be honest about not wanting to sell your property sliver. (That's ok! You don't have to sell. No one is going to make you.) Listen to his proposal on the landscape. Maybe what he's asking is not an expensive hard-scape but maybe just planting consistent plants across the hillside to make it all work together. Come to the conversation with your budget limitations. Be honest and let him know that you appreciate the idea of a cohesive landscape but that your budget is already stretched with the landscaping you have already done to your lot. Stand firm, but be polite. You will be stuck living next to this guy. See if you can come to some kind of middle ground where you keep ownership of your lot and you work together to make the properties look good without breaking your budget.

My own story: My last home shared a property line with a really nice family. We both had rather boring mailboxes right next to each other. The neighborhood had a rash of basic mailboxes getting knocked over and so our neighbor proposed that we go in together on some kind of masonry style mailbox. We said we thought it was a good idea. Well one day we came home and there was a new double mailbox being built without us having any input on the design or materials. As soon as the mailbox was done, the neighbor let us know how much we owed them for the mailbox. Initially we were really irritated. They should have consulted us about the design and cost up front, but unfortunately they didn't. Honestly I don't think they even considered the possibility that we might not share the same style. Oh well. We gave them the money and enjoyed having a nice mailbox that wasn't quite our style. It was a frustrating situation and I wish we could have worked on a design together, but keeping the relationship friendly was important.

keeping the relationship friendly was important

Actually you were bulldozed over by the "really nice" people, being allowed to dominate others is what bullies depend on - there was nothing nice or friendly about it, on their part.

Just look at your above description of what transpired, you are clearly not happy with the outcome - where is this friendly relationship you are trying to maintain?

I used to work under a bully. One day I finally "yelled" back at him, after which no additional verbiage came from his direction.

Later I found out from another employee that the bully had secretly approved of the manner of my response, that it had shut him right up. So it was like he was always testing people with his basic approach, to see if they would stand up for themselves. If he was in fact able to anger them, then at that point they deserved some respect.

Doubtless your neighbor also now thinks a precedent has been set, will act accordingly - should there be any future interactions involving them wanting you to do something.

I'd definitely assume he meant well and keep things friendly, since you'll probably be neighbors for a long time. I would want to hear what the landscaper proposes. It's not clear to me how they get from the street to the neighbor's property, so I'd want to make sure the landscaper doesn't need to cross your slice to get to his lot. Also, if they come up with a landscaping plan that makes your slice look cohesive with his lot, it might look like that land all belongs to him even if you own some of it.

Is the lot line clearly marked?

I like the idea of running the yellow tape between the posts. Some of the people landscapers hire would not pay attention to the posts at all. When the builder of our house put in the chain link fence on the south side they paid no attention to the property line but used the easiest flat area. At the curb I have 5 more feet on my property than I should. Both owners may have decided it was ok at the time but could cause problems later.

My first thought was about the hillside looking like it belongs to the neighbor, too, so right off I would not be interested. If it were me I would let the neighbor know I would be excited for them for their plans and wish them well, but inform them that I am focused elsewhere and won't be even thinking about that area anytime soon . or what I may eventually want or decide to do. They should go ahead with their plans. (For me I would want ALL MY property to be part of my OWN cohesive plan.) I would not give even a hint of any thought that I might consider their plan down the road - because I wouldn't and wouldn't want to give false hope or have them delay their own plans thinking I might. Frankly I wouldn't be surprised if they then abandon their"plan".