Container Gardening: A few tips for uncontained success

By Bliss Newton, Former Marketing and Membership Coordinator, Collective Manager

Portland is an urban environment, so many of us live in apartments or other spaces without space for large, in-earth garden beds. Many Portlanders rely instead on pots and containers to grow our edible gardens and ornamentals on stoops, balconies and decks.  And if you’ve gone this route, you probably already know that container gardening can pose some challenges.  Namely, these challenges have to do with container choice, water retention and fertility.

Here are a few tips for growing a better container garden:

1. Not all containers are created equal, so choose wisely.  

People often use containers that are far, far to small or shallow to grow container gardens, to unfortunate results. The deeper a container is, the better, because the increased volume helps prevent evaporation and allows roots to penetrate deeply.  This is especially important for plants that have deep roots like tomatoes, carrots, and parsnips.  Tomatoes--a favorite for containers--simply will not thrive in anything less than 1.5ft of soil depth. If you don’t use the proper container, (even if you have great container soil!), you could end up watering two or more times per day, or stressing the plant with dehydration and poor nutrition.  The appropriate container helps prevent low fruiting and pest infestation due to stress.

2. Sanitize your containers.

Give your containers (even new ones!) a good washing with soap and water, rinse,  very well and then sanitize with sanitizer of your choice.  Allow to air dry or wipe completely dry with a towel before planting.   If you suffered mold or powdery mildew last season in porous containers like terra cotta, you may want to dispose of them to avoid a repeat performance.

3. Choose (or create!) the right potting mix.

Soil for container gardening needs to be light enough to allow for lots of air flow, water drainage and root penetration, while still holding moisture longer than in-earth garden bed soil.  It can be tempting to go on Craigslist and look for free fill dirt, and load your containers this way.  Ground soil and fill dirt just won’t serve you well in the long run-- they tend to have poor soil structure, (which can lead to compaction and thus poor drainage and root penetration), and can be low in nutrients.  It’s also important to fight the urge to reuse last year’s soil.  Because containers are essentially a one-input system (last year’s plants depleted nutrients in the soil, and water is leaching away nutrients and organic matter year round, without replacement), you may find water retention problems and nutrient depletion.  If you suffered from any pest or mold/mildew problems, it is especially important to get new soil.

BEST PRACTICE: Take the long view and invest in a high quality potting soil that is intended for container gardening.  These soils are equipped with water retaining matter, like peat moss or coconut coir that will hold moisture and help prevent nutrient leaching.  They are generally much higher in organic matter and compost, which provide plants with nutrients.

3. Be prepared to fertilize.

Because containers are a closed system, and the plants are taking everything within that system, you may find the plants lagging mid season.  There are lots of earth-friendly, organic fertilizers available at various price points.  I like to purchase an organic, slow-release tablet fertizer and pop that in when planting at the beginning of the season--an offensive tactic early, instead of a defensive move later.

4. Observe and tend to your container garden daily.

Even with great soil, good fertility and the right containers, you will need to tend to your container garden more frequently than your friends with in-earth garden beds. (Not a burden, but a joy!)  Hand watering your container garden can take more time, but it gives you the opportunity to carefully observe your container garden and act quickly if you need to.

Other helpful hints:

  • Be mindful that containers are more exposed, so rapid changes in weather will effect your plants more than in-earth gardens.  Keep some old sheets around to cover plants on surprisingly chilly nights. 
  • Keep a mister bottle around and mist your plants to help create a moisturizing environment.
  • If your container garden is south or west-facing, be especially observant that your plants aren’t getting sunburned, especially when starts are young and tender. (Consider making a screen of some kind if they are!)
  • It is best to water in the morning--evening watering can attract pests, and mid-day watering can leave sun-magnifying droplets that will create burn spots. 
  • It is always best to water directly into the soil and try to avoid getting water all over the plants, as this can also create burn spots from sun magnification. 
  • Remove pest or otherwise damaged leaves and plant matter as soon as you notice them.

Do I need to water?

Stick your finger about 1.5-2  inches into your soil.  If your finger comes out with moist bits of soil on it, you are probably okay.  If it comes out just dry and dusty--time to water!!

Best plants for container gardens:

Plants known to thrive in the right container, with root penetration and recommended pots

  • Beans, snap: medium roots, any container or window planter box, 8” deep    
  • Broccoli, Cabbage, Kale: medium roots, 1 plant=5 gallon pot, 3 plants=15 gallon pot
  • Carrots: deep roots, any container or window box at least 12” deep
  • Cucumbers: medium roots, consider “training up”, 1 plant=1 gallon pot 
  • Eggplant: deep roots, heavy feeder, 1 plant=5 gallon pot
  • Lettuce: shallow roots, shade tolerant, window planter box
  • Onions: shallow roots, any container, window planter box
  • Peppers: medium roots, 1 plant=2 gallon pot, 5 plants=15 gallon
  • Radishes: shallow roots, shade tolerant, any or window planter box
  • Tomatoes: deep roots, bushel basket or 1 plant=5 gallon, 3 plants=15 gallon
  • Perennial Flower/Herbs: medium roots, any container 10” or deeper
  • Annual Flowers/herbs: shallow roots, any container, 6-8” minimum depth