Jul 2, 2024
Gardening in containers is great for so many reasons, not the least of which is that almost everyone can have the opportunity to grow something, including food! From the tiniest windowsill to the most expansive acreage, plants in pots can be any size and placed almost anywhere, including established landscape areas. Even better, containers can be moved around to take advantage of sun, shade and seasonal shelter. For those with access to in-ground planting, containers provide solutions to areas with poor soil, gophers and experimentation with different plants before committing to landscape changes. Opportunities for unique containers and intriguing floral and foliage combinations are endless-- maybe even a tad overwhelming. Whether it's a simple pot of herbs or a major statement, here are the essentials.
What Can I Grow?
Given the right conditions, pretty much anything that grows in the ground can be grown in a container, including most vegetables, annual and perennial flowers, succulents, roses, dwarf fruit and citrus tree varieties. What makes the difference between success and failure boils down to meeting the plant's requirements for light, water, drainage, soil and nutrients. Just like regular gardening, right? Yes, but… Containerized plants are just that, contained. Unlike plants in the ground, they can't go beyond the boundaries of the pot to seek what they need. Since they are above ground, they are also more vulnerable to temperature extremes.
What's the Best Location?
To determine what you will be able to grow successfully, start by observing the patterns of light and shade at various times of the day in potential locations. If you want to grow vegetables, look for areas that receive at least 4 to 6 hours of direct sunlight. The amount of space available is another consideration: you'll need enough to accommodate the size of the container for the plants you want to grow. If your space is small and shaded most of the day, sun loving plants such as tomatoes or roses won't work but lettuces and many succulents will be very happy. Avoid areas that are often buffeted by prevailing winds, which are likely to be west and northwest-facing spots.
Also: ensure that balconies, decks, steps, rooftops and other structures are sound and can support the weight of planted containers. When choosing your location, make sure that it includes a convenient source of water. Containerized plants need to be watered more frequently than plants in the ground and carting containers of water around gets old fast!
Pick the Right Pot
Almost any container can be used if there are holes in the bottom and enough depth to hold the soil and roots of the plant or plants you want to grow. This is especially important for edible plantings because a pot that is too shallow will affect the plant's growth and result in stunted, less productive plants. Shallow rooted plants such as lettuce and herbs can be grown in 6 to 10 inches of soil whereas indeterminate tomatoes need 18 to 24 inches. Perennials and taller plants usually have larger root systems than annuals so greater depth is required here as well. If in doubt, a good rule of thumb is to go bigger and deeper.
Use the Right Soil
No matter what you want to grow, only a good quality mixture formulated specifically for containers will do. “Potting mix” or “potting soil” is lighter, holds moisture, supports roots and allows for proper drainage. Do not use “planting mix,” “garden soil,” or “topsoil” as they are too heavy and will not provide what is needed in a contained situation. You may also want to add a bit of compost and plan on fertilizing more often than in-ground plants.
Irrigation Imperatives
How often your plants need water will vary depending on the plant variety, seasonal temperatures, how much sun is received and type of pot material. A good way to determine if your plants need water is to check the top inch of soil. If it feels dry to the touch, water is needed. When water runs out of the drainage holes, you will know you've watered enough. If, however, the top inch feels damp, you can wait for a bit.
Adequate Drainage
Good drainage is vital to any garden, but it is especially important for plants in containers. Since they need more frequent watering than plants in the ground, it's essential that moisture can flow properly. Make sure there are enough holes at the bottom and that the holes are not blocked. If pots are on impervious surfaces, elevate them a bit with small blocks of wood or pot “feet” to allow water to drain and prevent stagnation. A layer of rock or gravel is often put in the bottom of the container because it is believed to improve drainage. Not only does it not work, it makes things worse. Here's why: water moves easily through fine-textured potting soil which allows moisture to move down the container by gravity and capillary action. Rock, gravel and other hard materials do not have capillary pores so when water hits the hard stuff, it stops moving and forms a wet layer above the rock, thereby reducing the available room for plant roots and increasing the chances for unhealthy water logging. For the same reason, rock and pot shards used to contain potting soil can also block drainage. Use small pieces of screen instead.
Material Matters
In addition to size and depth, what a container is made of will affect what you want to grow. Considerations such as cost, weight, durability and overall aesthetics are important but understanding functionality is key. Here's a brief overview: Terracotta provides aeration but dries out more readily, whereas plastic holds in moisture. Metal is durable but can get too hot for many plants. Ceramics are colorful but difficult to drill holes to ensure adequate drainage. Fabric “grow bags” are inexpensive, easy to store and promote healthy root growth. Although homely, they are great for vegetables. Cedar or redwood planters resist decay and other types of wood can be used if not previously treated with arsenic-based preservatives. Lastly, beware of choosing pots with narrow openings. They may look great but once the roots have spread, you will have trouble extricating the plant when it comes time to divide or re-pot.
For more on container soils:
https://ucanr.edu/sites/ucmgnapa/files/81894.pdf
https://ucanr.edu/sites/EDC_Master_Gardeners/files/318396.pdf
https://ucanr.edu/sites/EDC_Master_Gardeners/files/318396.pdf
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Maggie Mah is a UC Master Gardener of San Mateo and San Francisco
Counties.
UC Master Gardeners of San Mateo-San Francisco County are volunteers who
are trained under the auspices of the University of California to provide science-
based information on plants, horticulture, soil, and pest management at no
charge to the public. For more information about classes and events in your area,
to sign up for our newsletter and get answers to all your gardening questions via
the Helpline, visit our website: http://smsf-mastergardeners.ucanr.edu/
Lettuces and herbs grow well in shallower containers. Plant multiples for frequent harvesting.
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Vegetables with similar requirements for sun, water and root depth can be grown together. Here, peppers and onions create a fun combo.
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The possibilities for creative containers are endless! Here, red ivy geranium (Pelargonium peltatum) floats above silvery dusty miller (Senecio cineraria) and trailing, sage green licorice plant (Helichrysum petiolane.)
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Size, material and adequate drainage are key criteria in choosing containers for plants.
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