Container gardening

Author: Dave Tomashefski

Planting native plants in pots can be a great way to bring beauty and wildlife value to a porch, patio, or other outdoor area, especially when space for in-the-ground gardening is limited. While benefits to pollinators are similar between potted and garden plants, maintenance needs differ. For instance, potted plants require fertilizing and regular watering due to the limited extent of the soil to which their roots have access. Here is an overview of the container gardening process.

Choosing a pot

Pots are commonly made of various materials, but porous materials such as unglazed clay or terra cotta will cause soil to dry faster than will non-porous materials, e.g., glazed clay. Also, dark colored plastic can get quite hot and may also accelerate soil drying.
Large pots are often preferable to smaller pots. This is because they are slower to dry out and they provide more room for roots. Plants grow best in pots that are at least 2” wider in diameter than the current spread of their foliage, but remember to plan ahead for future growth. In general, it is best to select the largest pot that won’t look out-of-proportion with the plant(s) in question at their expected midsummer size.
There should be at least one drainage hole in the pot. If the hole is large it may need to be covered with a screen or cheesecloth to prevent soil loss.
Ceramic containers may crack during the winter. If using a ceramic container choose a high-quality glazed pot with a wide opening and tapered base. This gives water space to expand when frozen and reduces the risk of your pot cracking over the winter. Terra cotta pots are particularly susceptible to cracking.
Placing a saucer or shallow bowl under potted wetland plants can help keep the soil moist and reduce watering frequency. The saucer is filled when the plant is watered. This is not recommended, however, for non-wetland plants.

Choosing plants

For placing multiple plants in a single pot, select plants that can handle similar moisture and sunlight conditions. Also, choose plants whose shapes are complementary and won’t simply compete for the same space, covering one another up. Finally, keep in mind the timing of the plants’ blooms. Blooming in synchrony can offer nice color combinations, but blooming throughout the season may lengthen interest.
Larger plants, e.g., > 3 ft in height, may require their own pot so that they don’t overwhelm neighboring plants.

Growing media

Soil from the yard tends to get compacted in pots and may also shrink from the sides of the pot when dry, making it difficult to wet the soil when watering. Soil-less potting mix is often a better choice because it resists compaction and is good at holding onto moisture.
If you are interested in a peat-free potting mix, we recommend FoxFarm Coco Loco, which uses coco coir instead of peat. At Meadow City, we use a peat-free potting mix to protect peatlands, which are globally important carbon-storing wetlands that are drained in order to harvest horticultural peat.
In order to ensure adequate nutrition, potting soil should contain fertilizer. Most potting mix is sold already containing fertilizer, and this will be indicated on the bag.

Planting

Pots should ultimately be filled with potting soil to approximately 1 inch lower than the top edge of the pot. To begin, thoroughly wet the potting soil and begin filling the pot. When the pot is partially full, remove the plant from its nursery container and set it on the surface of the potting soil. Check whether the level of the potting soil below the plant needs to be increased. Once there is enough soil in the bottom of the pot, finish filling up the empty space around the plant’s root ball with potting soil. When finished, the soil should cover the plant’s roots and should be even with the base of the plant’s stem.

Fertilizing

The fertilizer in your original potting mix will eventually run out and will need to be replenished. Your potting mix packaging should state show long the fertilizer is meant to last. If it doesn’t clearly state how long it lasts, add more fertilizer after the first month. Pale green leaves or yellow leaves out of season may also signal the need for more fertilizer.
To replenish fertilizer, you can top-dress with a slow-release fertilizer such as Miracle-Gro Shake n Feed Plant Food. When added to the surface of your potting mix, the granules will release fertilizer at an appropriate rate over the course of several months. Follow your fertilizer instructions to know how much to apply, how long it will last, and any other pertinent details.
The potting mix we have provided for you in the workshop will last until the spring. You will need to add more fertilizer in the spring, as the plants begin coming up.

Watering

Plants will generally grow best in moist soil. The goal of watering is to keep the soil moist.
Potted plants usually need to be watered on a daily basis – less if it has been raining or if the planter is in the shade, and more if it has been very hot or windy. If the soil is dry to the touch and the plant looks droopy then it needs to be watered, even if it has already been watered for the day.
The soil should be thoroughly wetted at each watering session. Allow the water to drain out through the drainage holes for a few seconds in order to keep salts from building up in the soil. If a saucer is in place underneath the pot, regularly rinse the salt residue off of it so that it doesn’t get reabsorbed into the pot.
Watering in the morning is better than watering in the evening because it will lessen the chances of root rot and will ensure the soil is moist during the heat of the day.

Wintering

Most native plants will be able to overwinter outdoors just fine. You’ll need to be careful if you are at the northern edge of a plants’ natural range - that is, if it’s a southern plant that only grows as far north as Ohio. As a rule of thumb, plants will overwinter well if the plant’s natural range includes areas that are two USDA plant-hardiness zones colder than that location. To check a plant’s natural range, look up the scientific name in the BONAP North American Plant Atlas. Plant Hardiness Zone Maps are hosted online by the USDA.
If there is concern about a potted plant perishing over the winter, consider moving the plant into the garage, beside a building, or burying it with fallen leaves for insulation from the cold. Do not bring the plant indoors, as the plant may not enter dormancy but will not get enough sunlight to grow indoors.
During most winters, container plantings don’t need any watering. Consider moistening the soil only if there is an unusually long period with no rain or snow.

Long-term maintenance

When the plant’s spread clearly exceeds the diameter of the pot and/or the plant’s roots are creeping out of the drainage holes, it’s time to consider re-potting into a larger pot. Select a pot that is at least a couple inches wider in diameter than the spread of the plant’s foliage.
Many native plants send up additional stems each year and it may not be practical to keep increasing the pot size. In these cases, the plant should be divided during cool weather in the spring or fall. To divide the plant, remove it from the pot, keeping the roots intact. Then, using a serrated knife or small saw, cut vertically through the root clump, making sure that the divisions allow the stems to remain connected to a significant portion of the roots. For example, if the clump is divided in half, then half of the stems would ideally remain connected to half of the roots. One half of the plant should be replanted, and the other half should either be planted in the garden or discarded. Once the plant has been divided and re-potted, it should be placed in the shade for several weeks. This will allow the roots to recover before the plant resumes active growth in a sunnier situation.

For more tips on sprucing up a balcony garden, check out this guide - to which we contributed!