Before you begin, it's helpful to stick the plants (still in their pots) into your final containers and move everything all around. Do you have beans that will need a tall support? Twining squash vines that might look good in a high place? Chives that need to be kept cool? Group your plants by how much sun they need, especially if you'll be planting multiple plants in a single container. Mix low-growing plants with tall-growing ones to maximize your space. Take your time and have fun with it!
Once you have your plants laid out the way you'll want them to be, it's time to dig in.
Most bags of soil marked 'potting soil' will work for your purposes. Some have slow-release fertilizer already mixed in, and some don't. I prefer to use organic potting soil myself, and large companies like Miracle-Gro now provide organic potting soil at large chain stores such as Home Depot. If you go to a local garden center, however, they will be able to give you better guidance on the best soil for your plant type, container type, and local conditions.
If your potting soil doesn't have a slow release fertilizer already mixed in, you'll need to add a bit. First, add a few inches of potting soil to your container, tamping it down very gently with the backs of your fingers. Shake in about a tablespoon (for the container size shown here) of slow-release fertilizer granules, such as Osmacote- they have varieties specially formulated for veggies or flowers. For a more organic approach, use a seaweed-based fertilizer instead.
Pop the plants out of their plastic containers by turning them upside-down, pushing on the bottoms, and gently (very gently!) pulling on the base of the roots. Delicately wiggle your fingers around in the tangle of roots at the base of the plant to loosen them from their tight container-like configuration, and place the plant on top of the fertilizer.
When you have each plant in the container, fill in the gaps around the plants with more potting soil. You'll want to jiggle the container slightly or tamp down the dirt with your hands to fill any air pockets with soil.
Alternatively, you could plant different species in terra cotta pots and then plant those pots in a longer container. This will cut down on the frequency of watering, since the larger container will hold more water, but it will severely limit the size of your plants. That may be a good thing, depending on what you're growing. A highly invasive plant, like mint, can only be trusted not to take over the entire container when it is planted in this way.
To discourage any weed seeds- they are sometimes imported in your potting soil or even lurk at the base of your new plants- reduce watering, and repel predators, cover the raw dirt with some form of mulch. This could be wood chips, gravel, or even tumbled river stones. White rocks look very tidy and as an added bonus reflect light back onto the plants, which can maximize your sunlight in a shady garden. Mulching your plants will give a finished look to your garden and save you work down the line.
