Durham NC – Extension Master Gardener Volunteers of Durham County

By Deborah Pilkington, NC State Extension Master Gardener^SM volunteer of Durham County

Container gardeners, me included, give a lot of thought to choosing which plants will go into the containers. But not a lot of thought is given to the containers themselves. Yet, to have a successful container garden in full sun, shade, or anywhere in between, the choice of pot is as important as the choice of plant. So, for the next few minutes, we’re going to look at factors that should be considered for container choices, especially in our newly-designated hardiness zone 8.

Porosity

*Examples of porous pots*. (Image credit: Deborah Pilkington)

Some containers, such as the familiar terra cotta (“baked earth” in Italian) are very porous, meaning the pot draws water from the potting media through its walls. Other porous materials include hypertufa, unglazed ceramic, and clay. Because of this, these porous pots may require more frequent watering, something to think about if they are going to be in full sun. Less porous choices would be wood or concrete, and the least porous pots are made of metal, fiberglass, plastic, or glazed ceramic. That means they are going to help the potting mix conserve water.

Size

The smaller the pot size, the more frequently it will need to be watered, sometimes more than once a day. A larger container is going to be heavier and less likely to tip over. Larger containers will require less frequent watering but can be a bear to move from location to location…unless you own one of these (see the photo below). And the cost of filling the container with potting mix is also a consideration.

*The difficulty of moving very large pots!* (Image credit: Deborah Pilkington)

Fragility

If a container is fragile and susceptible to cracking in cold temperatures, it will need to be moved to a sheltered area for winter. Terra cotta, clay, unglazed ceramic, and hypertufa are all fragile materials. The sturdiest are metal, plastic, concrete and wood.

Heat Holders

Metal containers, and dark-colored containers are heat holders in full sun. They can even be hot to the touch! Potting mix in these containers can rise to well over 100°F. Keeping roots well-watered, unless you are growing cactus, is a must.

Shape

If you are going to grow a shrub or tree in a container, at some point the plant will need to be lifted from the container to be root pruned—an onerous but necessary task. So, for shrubs or trees you want to choose a container that is wider at the top (below on the right) rather than narrower (below on the left) to make lifting easier.

(Left) This container is more narrow at the top and would make it difficult to remove a shrub that had grown in the pot. (Right) In contrast, this pot is wider at the top than the bottom and it would be easier to remove a shrub that had been grown in the pot. (Image credit: Deborah Pilkington)

Drainage

Good drainage is a must in container gardening. If the container doesn’t have drainage holes, you can add them using a drill and the appropriate drill bit. And to ensure correct drainage, don’t put anything in the bottom of your container but soil mix. Adding gravel or covering the hole with broken terra cotta not only defeats the purpose of ensuring drainage, but it also raises the level of the perched water table, moving the level of saturated soil even higher in the container and closer to the roots.

*Drilling holes in metal containers at Cocoa Cinnamon Demo Garden on Geer Street.* (Image credit: Deborah Pilkington)

For gardeners with limited space, especially the newcomers to Durham’s condominiums and apartments with balconies, container gardening can bring some beauty and food to your home. For urban container gardening inspiration, visit the International Award-Winning Master Gardener^SM Container Demonstration Garden at Cocoa Cinnamon at Foster and Geer streets in Durham.

*Get more ideas on container gardening by visiting the Cocoa Cinnamon Demonstration Garden at 420 West Geer Street in Durham, NC.* (Image credit: Deborah Pilkington)

Resources and Additional Information

Check out the links below to learn more about plant hardiness zones including the history and factors used to determine the hardiness zone of an area. What does this really mean for North Carolina gardeners?

2023 USDA Plant Hardiness Zone Map | USDA Plant Hardiness Zone Map

Gardening Association of North Carolina – 2023 USDA Plant Zone Update (gaonc.org)

AN ILLUSTRATED HISTORY OF AMERICA’S PLANT HARDINESS ZONES (With a Closing Look at North Carolina) | by Tom Packer

For more information on perched water tables and soilless media check out the below online guide about drainage for containers.

How to Improve Drainage in Plant Pots, The Proper Way to Do It! – Deep Green Permaculture

If you want to take a deep dive into the physics of water movement in soilless media and media components, visit the following links.

Growing Media (Potting Soil) for Containers | University of Maryland Extension (umd.edu)

Homemade Potting Media (psu.edu) — How to make your own potting media

Learn more about choosing pots with the in-depth article below.

Containers, Pots, and Planters: What Material Is Best? (gardenerspath.com)–

Article Short Link: https://wp.me/p2nIr1-4sZ

by Lissa Lutz, NC State Extension Master Gardener^SM volunteer of Durham County

If you’ve ever tried to reduce your carbon footprint, you know that it can take patience, persistence, creativity, and sometimes compromise. As the plant sale committee works to make our community a greener place with plants, we are also trying to keep our efforts green in the process.

As our Backyard Treasures Plant Sale name implies, much of our inventory has traditionally been sourced through generous donations from Master Gardener^SM volunteer gardens. In recent years, however, we’ve grown to understand the risks of transferring unwanted species far and wide–not just invasive plants but also unintended species such as weeds and soil-dwelling creatures that may come along for the ride. The first way to combat this problem has been to increase the number of plants we start from seed.

Starting Plants from Seed

Our veggie and herb selections have always comprised almost a third of what we sell and are lovingly home-grown by a dedicated team of seed starters. In addition we now have a team growing a variety of native plants from seed. Many of these plants are challenging to start, their seeds often requiring complex temperature cycling to initiate germination. We also rely on our propagation team, another spin-off from the plant sale committee, for providing us with a variety of propagated plants. All of these plants, whether started from seed or propagated, are grown in clean potting mixes that reduce the spread of unintended species.

A variety of native seedlings get their start under grow lights before transitioning outdoors and then they will be sold at the Backyard Treasures Plant Sale! (Image credit: Lissa Lutz)

Growing Plants by Division

Many wonderful plants that we share are still sourced through the division of garden-grown favorites, and those plants are now thoroughly washed to remove all soil from the roots before they are potted up in fresh potting mix. While not perfect, this system can vastly decrease the chance of sharing undesirable plants and organisms.

Root washing to remove contaminants reveals the beautiful intricacies of the root systems. Clockwise from left: aromatic aster (Symphyotrichum oblongifolium); Canadian wild ginger (Asarum canadense); Formosa lily (Lilium formosanum); celandine poppy (Stylophorum diphyllum); Columbine sp (Aquilegia sp). (Image credit: Lissa Lutz)

Searching for the Right Potting Mix

Two years ago the committee began efforts to move away from peat-based potting mixes. Peatbogs, the source of peat for these mixes, are unique ecosystems and carbon sinks that are extremely slow to replenish. The committee had fun developing its own formula of a non-peat-based growing mix using coconut coir, perlite, vermiculite and compost. We tested the look and feel of various mixes to try to replicate the consistency of our traditional brand.

Soil mixing party with Durham Master Gardener^SM volunteers Bev Tisci, Lissa Lutz, and Durham County Extension Agent Ashley Troth. (Image credit: Lissa Lutz)

Scaling up proved to be challenging, time consuming and very dusty! There is a reason the best mixes are proprietary secrets, and indeed the seedlings in our concocted mix languished. For now we continue to start seeds in a peat-based mix for best results, while still searching for an economical and sustainable alternative. We have found an acceptable non-peat-based mix that we use for divisions and potting up seedlings once they are established.

From Plastic to CowPots®

This year, our focus has been on reducing our reliance on single-use plastics, specifically with respect to the pots we use. Most garden pots and flats are difficult to recycle because of the mix of plastics. Our approach to this problem will be twofold. First, we are trying to use a single pot size more consistently, namely what we call a quart pot. We are tagging plastic quart pots this year with a label that reads, “Return clean, intact quart pots to 721 Foster Street by May 31st.”

Our hope is that our local buyers will rinse and return the pots once they have planted their purchases. With a little extra care we should get at least one more season out of them and are excited to see what percentage of pots come back to us. In addition, we are spreading the word about how pots and flats can be recycled.

Second, we are piloting a biodegradable pot in our sale. After researching a variety of biodegradable options, we landed on CowPots®, a pressed pot made from dehydrated cow manure sourced from a dairy farm in Connecticut. The size is roughly equivalent to our plastic quart pots. They can be fragile to handle especially when wet, but the entire pot can and should be planted in the ground with the plant and should be completely degraded by the end of the growing season.

Plants grown in CowPots® are reported to have healthier root systems because of air pruning, a process that starts when the roots begin to grow through the sides of the pot. When the root tips meet air on the outside of the pot, it stimulates lateral growth from the root back inside the pot, as opposed to the circling of the root that occurs when it meets the side of a plastic pot. Additionally, the pot itself provides amendments and a small amount of nutrients to the garden soil as it slowly decomposes. These pots are only slightly more expensive than the plastic pots. It will be interesting to see how they are received by the public. Only a small percentage of plants this year will be grown in the CowPots, to give us a chance to evaluate them and address any problems that arise.

(Left to right) Canadian wild ginger (Asarum canadense) in the back and perfoliate bellwort (Uvulariaperfoliata) in the foreground growing in CowPots®; Pink turtlehead (Chelone lyonii) and mountain mint(Pycnanthemum muticum) getting established; CowPots® allow roots to penetrate their containers as they grow and prevent damaging root circling that occurs in plastic pots. (Images credit: Lissa Lutz)

Adding these green initiatives to our plant sale practices has not necessarily made the work easier, less expensive, or even better in some cases. But it does feel like we are moving in the right direction to be responsible stewards of our land and to set an example for our community.

Resources and Additional Information

To learn more about the environmental impacts of plastic horticultural pots, check out “2023 State of the Pot” by the Association of Professional Landscape Designers’ and Healthy Pot, Healthy Planet Initiative.

https://www.healthypotshealthyplanet.org/_files/ugd/5ceae1_56fb60127c1f4794a94b0c38b3cd90a0.pdf

For more information on Cowpots®, an example of a more environmentally garden pot, visit their site.

https://cowpots.com/marketing

To learn about additional ways to be green in the garden, see our August 2022 blog post “Minimizing the Use of Plastic in the Garden” by Extension Master Gardener^SM volunteer Wendy Diaz and NC Cooperative Extension’s factsheet.

https://durhammastergardeners.com/wp-admin/post.php?post=9832&action=edit

https://pender.ces.ncsu.edu/2021/10/recycling-plastic-plant-pots-and-containers/

Article Short Link: https://wp.me/p2nIr1-4p9

Extension Master Gardener Volunteers of Durham County

Category: Durham NC

Give a Thought to the Pot