Common mistakes when planting containers. Since I have made every mistake possible, many more than once, the following list of 10 common container gardening mistakes is just a start, and is in no particular order.
1. Filling a large container in the wrong place: Ever tried to lift a large container garden filled with dirt and plants? I have, and it can be overwhelmingly heavy. When using a large or unwieldy container make sure to place your pot where it will live and then fill it – you’ll save your back!
Also, if you know you are planting shallow rooted plants in a very large container (for example, herbs, annuals, succulents), you can fill the bottom third with empty plastic bottles and cover them with plastic screening. You can also use a product called "Better Than Rocks," to take up space. It will make your container lighter and less expensive because you won't need as much potting soil.
2. Overwatering Your Plants: To avoid over-watering your container gardens, use containers that have drainage holes – lots of them. Also, make sure to read the moisture requirements for your plants and then follow them. Before you water, check if your soil is moist. To do this put your finger into the soil up to your second knuckle. If the soil at your fingertip feels dry, water your plant.
If you do over-water, leaves may turn yellow and fall off, or your plants may get limp. If your soil is too wet, move the container to a dry, breezy spot until it dries out.
If you have the room, you can also move your container garden into a garage or sheltered spot to dry it out, particularly if the weather is continuing to be wet.
3. Underwatering Your Plants: Most container gardens need watering at least once a day in the heat of the summer.
Many, especially hanging planters or small containers, need watering even more often because there is less soil to hold moisture. When you water, make sure to really soak your plants – if you just give them a sip, the water will only wet the top layer of soil. Water until you see it coming out of the bottom of your pot.
Lots of people use water crystals but they are expensive and some tests have shown that they aren't particularly effective.
If your plants do dry out, don’t despair; even the most pathetic, limp, plant might revive with a good drink. If the container is small enough, submerge the whole thing in a bucket of water until the air bubbles subside. For a large container take a skewer or stick and gently poke holes deep into the soil to allow water to reach the roots. Then water generously.
4. Awkward plant to pot ratio: Make sure to consider the proportions of your plants to your container. A large container stuffed with short plants can look stunted. If you need a rule of thumb (and remember that rules are meant to be broken) try to have at least one plant that is as tall as the container. Also try plants that will spill over the sides.
5. Buying weak or sickly plants: Buying plants at a reputable local nursery is a good place to start in your quest for healthy plants. You have a greater chance of getting plants that are disease and pest free and well cared for than at a big box store. At a nursery, you can often get a wealth of information and advice from knowledgeable staff. Don't be afraid to ask someone to help you pick out a good plant.
If you can’t resist the prices of buying plants from a big box store (and occasionally, who can’t?), try to buy them on or close to the day they’re delivered. Don’t be shy to ask someone who works there which day new plant stock arrives. Delivery is usually the same day every week.
6. Fear of pruning: When your container gardens start looking leggy or ragged, don’t be afraid to cut them back.
You may want to put them in an out-of-the-way spot until they re-bound, but chances are they’ll come back healthier and happier with a good haircut.
7. Selecting plants with different requirements: Make sure that all the plants in your container garden share the same sun, soil and water requirements. You can find out this information from your seed packets or plant labels.
8. Starving your plants: Most potting mix has very few of the nutrients that plants require to grow and be healthy so you will need to add those nutrients to the soil. There are many fertilizers to choose from and flowering plants have different needs than vegetables and herbs.
In container gardening what nutrients there are in your potting soil are either quickly used by the plants or are washed out with repeated watering. Fertilizing container gardens regularly is a key to their success. You can start with a slow release fertilizer mixed in with your potting soil and then add a diluted, liquid fertilizer, such as fish emulsion, every couple of weeks. I use organic or all natural fertilizers.
9. Living with ick: After you’ve tried everything, short of mouth-to-mouth resuscitation and your plant still looks dreadful, cut your losses and toss it on the compost pile or in the trash. If only one plant in your container garden is icky, just pull out that plant and replace it.
10. Having unrealistic expectations: Before you make your container gardens, evaluate how you live. Do you travel a lot during the summer? If so, either get self-watering containers, an automatic drip irrigation system, enlist some help to keep your plants healthy and alive while you’re gone or get plants that don't need a lot of water.
Garden how you live. Are you casual or formal? I take a loosey-goosey approach to gardening because it fits well with my personality. I like big overflowing containers with riotous colors and luxuriant blossoms. Some people like neat, well-planned, formal containers.
I grow vegetables and herbs galore because I like how they taste and the experience delights and fascinates me.
Remember, this isn’t brain surgery –- there’s lots of room for error. Have fun and experiment. Whatever your lifestyle or personality you can make container gardens that will give you joy and bring beauty to your surroundings.
taken from https://www.thespruce.com/common-container-gardening-mistakes-
Till next time this is Becky Litterer from Becky's Greenhouse, Dougherty Iowa