Planting advice is like cooking with a recipe. There are tons of different recipes and most of them give great end results.
Here is a basic recipe for planting things. If you have a different way and it works for you, there's no reason to change.
PLANTING ANNUALS IN CONTAINERS
#1. Make sure your pot has proper drainage.
Whether you have an existing pot, or are purchasing a new one, be sure that your pot has drainage holes in the bottom. Some will come pre-drilled and may or may not have plastic plugs in the holes, if it does have plugs be sure to take them out. If it doesn’t have holes, drill some! Use at least a 1/4" drill bit and punch some holes in the bottom. If you have a plastic, resin, or metal pot, any regular drill bit will work fine, but if you have a ceramic, concrete, or terra cotta pot, be sure to use a masonry drill bit.
#2. Start with good soil
Start off with a good potting soil. Using a cheap soil (like topsoil) is a great way to ruin all the beautiful plants you just bought, you'll regret it. Trust me.
We recommend using Baccto Lite Potting soil. It's what our growers use and the plants they send us look great.
#3. Plant it!
Take the annuals out of their pots. Turn them upside-down to gently release them into your hand. If they don't come out easily, squeeze the sides of the pot to help loosen them up a bit. You don't want to pull too hard on the plant because you can damage their roots.
Now that it's out of the pot, take a look at the roots. If you see roots circling around the plant (like in the image), be sure to break them up a bit before planting. Use your fingers, or if they are severely root bound, use a knife and make 2-3 vertical slices down the rootball. It's OK to break some of the roots, they'll regrow new ones!
Now plant them in the potting mix so the top of the soil in their root ball matches the soil level in the new pot. Avoid mounding the soil up around the stems of the plant. It can cause problems later.
#4. Fertilizer
Now is the time to apply a slow release fertilizer like Osmocote. Most potting soils contain a starter fertilizer in them, but it's a pretty low concentration and doesn't last that long. So, put something like Osmocote in with your soil and forget about fertilizing for a couple of months! If you have your own favorite kind of fertilizer, apply that now instead, following the package directions.
#5 Water well
Proper watering is key to healthy plants. Be sure to water your plants well otherwise all the things you just learned won't matter that much.
Remember that the soil you just planted with can be relatively dry. Make sure you saturate the entire soil volume with water, not just the top 2-3 inches. Filling the pot up with water a couple of times usually works well.
Now you know all about planting annuals in containers. Next, let's learn about planting in the ground.
PLANTING IN THE GROUND
#1. Dig a hole
Dig a hole 2x as wide and 2x as deep as the pot the plant is in.
#2. Check the roots
Just like we did for planting annuals in containers, we need to check the roots of the plant before we put it in the ground. This especially true for trees and shrubs as they spend a longer time growing in the pot.
#3. Plant it!
Place the plant in the hole so that the top of the root ball is level with the soil in the ground. Make sure that the lower stems of the plant do NOT get buried. The height of the plant in the hole can be adjusted by adding or removing soil from beneath it. Remember, your hole will initially be too deep so you have to add some soil in first.
#4 Fill it in
Mix the soil from the hole with a couple shovels of whatever kind of compost you want (peat moss and mushroom compost are my favorites, but any will work just fine).
Throw some starter fertilizer in the hole. Bonide's Plant starter is a great conventional option, or check out Espoma Biotone Starter for a great organic option.
Now fill the rest of the hole up with a mixture of 2/3 soil and 1/3 compost!
#5 Water well
Give the plant a good, deep soaking. Watering very thoroughly just after planting helps the soil settle down and eliminates any air pockets.
Check the new plant daily for water. If the soil is dry, continue to water thoroughly as needed.
Now you're a planting expert! So what are you waiting for?
Get out there and plant something!