The last thing that I think that you need for a successful and easy to care for garden, is in my opinion, the hardest. The goal in your beds is to have no openings were you can actually see the soil or the mulch. The plants should grow together, just until they meet, and maybe mingle a little bit with each other. This is very difficult for me, because I have always read that you need to keep plenty of space between plants for good air movement. They need this to keep from getting mildew, and other diseases that plants get from being to close together.
When you plant your garden, you should usually know a little something about what you are planting. How big it gets, how much sun, type of soil, etc. Plants rarely follow the rules. If they like were they are planted, they may get twice the size that the tag says that they will get. So even if you follow the rules, and leave plenty of space between plants, they usually grow where they want to grow.
If you put the plants to close together to begin with, you can really have a problem in a few years. The old adage, "the first year they sleep, the second year they creep, and the third year they leap" is very true.
The other problem is that all of the garden magazines and books show these beautiful gardens. They set us up to think that that is the way our gardens should look. The pictures are usually taken on the one day of the year when the garden is perfect. Every plant is blooming, and disease-free. In the real world, this does not happen. How many times is one area of a bed in your garden gorgeous, and right beside it some plant has either decided to die, or the rabbits have chewed it to the ground, screwing up the whole effect? It is rare when all of the plants in our garden cooperate with each other, and all look great at the same time. To me the hardest part of gardening is to get something blooming, in the right color combination, at the right times. My husband says that I move plants around more than I move furniture in the house. I have been known to move a plant a couple of days after I planted it "for good" in a spot. I always apologize, and tell them that this time it is really "for good", but they know better. They know that next week I might decide that they would look much better in that bed on the other side of the lawn.
Sorry, I kind of got off on a tangent there, my original point was getting the plants to fill the space, without growing close enough together to cause disease problems.
If you accomplish this in your garden, and you have mulch down to keep the weeds from sprouting and hold in the moisture, and you have a good edge to keep the grass and weeds from creeping in from outside, your well on your way to a semi-maintenance free garden. You can spend your time in the garden doing things like dead heading, fertilizing, watering, and pulling the stray weed that always shows up no matter what you do.
So, if you have accomplished this, please give me a call, because I haven't, and I sure could use your help.
(The pictures that I used in this post ARE NOT from my garden. They are from books, were all the "perfect' gardens are)