You have to tell us where you are, as in, zone and nearest big city. You could be in Florida or Vladivostok.

Flower carpet roses can be grown in large containers.

https://www.tesselaar.com/plants/flower-carpet-roses/flower-carpet-appleblossom/

Just gorgeous. Also check out the container gardening forum.

https://www.google.com/search?q=flower+carpet+rose+in+container&client=safari&hl=en-us&prmd=sivn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjv_ervkoPcAhUkxoMKHehQARoQ_AUIEigC&biw=1024&bih=622#imgrc=wklCWsgOMD95IM:

Meant to post this one especially.

I like Goug’s rose tree idea. You could add on rose climbers too by the wall. Check out David Austin Roses.

Your garden is not very small. Many English city gardens are much smaller. You could check an English design book at your local library for ideas and inspiration, not for copying. I guess that you're in Romania? I'm in Sweden myself and not much help, but I would cover the fence first of all, for some privacy and color.

Thank you all so much for the ideas. Actually I'm in Europe, Romania.

@mariannese you're right :) Romania

@dig dough's designs - thank you, what kind of flowers did you put there, please?

What an exciting prospect—a blank slate! And just the perfect size to be very manageable. If I might make this suggestion, that while you are planning, start building up your soil. The success of any of your plants will be dependent on the health of your soil, so either do a home test or send off a soil sample to be tested, and start now adding as much organic material as possible.

@Perma n'Posies , yes you're right I need to build up the soil.

This map will tell you what zone you are in so you know what plants you can use.

https://www.plantmaps.com/interactive-romania-plant-hardiness-zone-map-celsius.php

Do you plan on putting in a patio or sitting area in the back for a table and chairs? Do you want a lawn area? Trees for shade? 150 square meters is about 40 ft x 40 ft if it was square, but it looks like it is longer than it is wide. Do you know how wide it is?

Is there a local plant nursery where you can look at what is available and get advice on choosing specific plants? Do you have access to mulch? A lawn mower? How much time do you want to spend taking care of it? Lots of things to consider when making a plan.

Hi @Saypoint,

I would love to have also a sitting area in the back with table and chairs and barbecue. The shape of the yard is rectangle, around 16 meters x 9 meters. A lawn area sounds nice, but I wouldn't want to spend too much time taking care of it, only in the weekends a few hours... I would also love to have a small area with vegetables maybe... during the morning I have full sun there, after 12 o'clock I have sun only on the half of the yard...

You need to start somewhere with an idea of what you want it to look like. Can you get some gardening and landscaping books and magazines or look online for pictures of smallish gardens to see what you like? Then narrow it down to what’s possible in your space, given your budget and amount of maintenance you’re willing to do?

Landscaping is not designed in complete disregard of whatever is the backdrop. The first picture is not the one someone would use in order to landscape the front of this house. You'd need to turn the camera around so that it is aiming toward the house. Because of the wall you'd need to stand at the gate and show the area in slightly overlapping photos, panning from left to right such that everything is included except what is near your feet, showing as much of the house as possible. You'd also want to take another picture by backing up and standing in the street that shows your whole property in a single shot.

For the back yard, you'd need to do basically the same. From about midway out into the yard, turn around and show the back of house from lot line to line. If you can't capture it in a single picture, show it in two slightly overlapping pictures.

If that back yard has shade on it from noon on, at what portion of the yard is the shade located? And where is it coming from?