Is refinancing possible after just 2 years? (for outdoor facility)

Does 10 years of lunar landscape really mean that you cannot save the 25k€ in 10 years? Or was that just an exaggerated statement? If the former, then a consumer loan would not be an option either, as you would have to repay the loan including interest at the latest in 10 years. In that case, be sure to follow the tip from Hausbautraum20. I would talk to the bank; maybe they will re-evaluate the house due to the higher costs and the market value increases, and you could increase the mortgage. Then it might be possible to arrange additional financing and thus stretch out the repayment compared to a consumer loan.

If all this is just wishful thinking

That's how it looks.
(Anyone could just come around the corner... obviously the bank doesn't do that!)
Only (possibly) a second follow-up financing remains (additional costs due to land charge) or a consumer loan, which you then service with the 200€.

Tip: Before it doesn't suffice again, first get offer(s) for the entire outdoor area, then determine the amount.
Good luck.

I would plan in stages: what is really necessary (probably the retaining wall), then the rest. For 25 thousand you can already get a whole garden that is set up. You don't need that. For less than half, the retaining wall is built and a terrace laid with second hand stones. The rest will green itself if you do nothing. Maybe there will be budget in the new year to do the rest. No one needs turf, planted half-grown plants, and a grill. That would all be nice, but probably not possible. I would definitely avoid taking on extra debt + interest burden in addition to the tight financing. You can really get almost everything for the garden second hand. Terrace stones in all shapes and colors, plants, soil, and sometimes also tools. For example, I was able to buy 20m2 of terracotta bricks for my terrace for 150 euros. New costs about 15-30 euros per square meter.

I spontaneously thought the same as Bertram. Being able to afford a garden landscaper means calculating carefully. You miscalculated, so use Plan B and/or C. Otherwise, it will become an endless rat’s tail for you. Eventually, refinancing every two years or early repayments or interim financings or consumer loans to bridge the years between due dates. Then you will never get down. Plan B: create a terrace, splash guard, and driveway with affordable material, e.g., gravel and/or recycled material and simple concrete edges. This can be done by yourself, man and woman, father and brother, friend and nephew alone. And whoever can’t do it will learn. Two left hands are better than none, etc. Ebay Classifieds helps a lot, also with plants and equipment. Plan C: take a side job, at least €450/month, and put it all into the house account. This also applies to any parents on parental leave. Because ultimately it still applies: where there is no money, there has to be work. I see further indebtedness very critically.

ING also has the [Wohnkredit], if you live there for a year, you can apply for it. Interest rates are not great, but less than the typical consumer loan. Take a look at it on the website. You do not need a [Grundschuld].

Because in the end it still applies: where there is no money, work must be done. I see further indebtedness very critically.

Yes, I agree. Better a modest garden with a makeshift solution than the risk of over-indebtedness and then possibly losing everything in a forced auction. There are many ways to save money and some to earn money. I find 25,000 EUR very little for a garden landscaper, how big is the property? I can well imagine that there will be some additional costs during the project. Especially since you obviously want to move large amounts of earth (retaining wall etc.).