Speaking as a landscape designer, all I can contribute is that computer applications are just that........just a tool that helps with visualization. They are not a substitute for an understanding or background in design. Unless you have some basic design skills under your belt, computerized design programs are just an electronic form of paper and pencil.

The best planning tool I can suggest - with regards to landscape design - is to acquire and study a text book (or a very detailed website) that takes you through the basic design process. That will at least provide you with the basic principles and the elements you need to apply to your computer program in order to generate a viable working design plan.

I would assume interior design has similar requirements.

There is definitely an advantage to CAD as one can create objects, as opposed to just drawing pictures comprised of lines. Sketchup is the free or low cost CAD program, but it has a high enough learning curve to be discouraging to many. Though there are tutorials online. It might be one of those things that if you grasp some of the basics, it will begin to "flow." I don't know; I've never made it that far.

Though it is just drawing, I like using MS Paint for plan and visualization, as it is simple ... good for anyone who understands perspective drawing. A simple base plan, since it is mainly lines, can be drawn on it with any computer, using the line and shape tools. The app has a built-in grid and measuring guide that can be toggled on and off. (The default scale is 1"=10', but it doesn't tell you that.) Compared to pencil and paper, it saves a lot of time if needing to erase, or when copying elements. And it is much cleaner. Since it's just drawing, it is not as precise as cad.

For visualization, you can open any landscape photograph in Paint and draw over it, and copy and paste elements within it. However, since that process is not just drawing straight lines, it requires a touchscreen and stylus in order to use the program well.

I wouldn't rush into a computer program. I've been using AutoCAD since 2004, and we also use Sketchup and some other 3D and rendering software here at Rev G World HQ. But our workflow is typically hand drafting on trace paper -> then AutoCAD -> then 3D or visualization software once the hard parts are worked out. Everyone's time is finite, doing a course on hand drafting through Udemy (or even finding some YouTube videos) will give you more bang for your buck vs the the time for the learning curve for a program.

The lower priced options of this software will be very helpful to you:https://www.ideaspectrum.com/professional-landscape-software/

As GG mentions, these tools still require a knowledge of plants & design principals in order to get the best finished product. However, trial & error on a computer versus trial & error installing plants pays for the software immediately.

For garden bed/plant visualization, I use mylandscapedesign.com (app.mylandscapedesign.com). It has a tool to visualize the garden layout and gives you lists of plants for your growing zone along with a list of everything you need/amounts to buy at the end.