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Making your garden pleasing to the eye
If you are really planning a container garden (instead of just an assortment of plants in pots), you'll want to be sure to keep the big picture in mind - just like a garden in the ground. Think about how different plants will look next to each other Of course, the good thing is that you can experiment - if that tomato overpowers your delicate flowering chives, just pick up the pot and move it closer to those purple basil.
The amount of space you're working with is important as well. As you choose your pots and plants, think about whether your 5-foot porch can really handle 3-gallon tubs of sunflowers (unless, of course, you like the jungle atmosphere). Scale is the key - the pots and the plants should fit the surrounding. But don't go to the opposite extreme and get 15 brown plastic pots in which you grow only 18" green plants - boring is NOT the goal!
Remember that just because your mom taught you that roots need soil, that doesn't mean that the soil can't be in the air - think about adding hanging baskets to create an extra dimension of variety. Be sure to include plants of different textures and heights, regardless of whether you are planting, flowers, herbs or vegetables. Different varieties of plants often have different colors and textures that can add spice to your garden.