Container Gardening | Healthy Plants & Beautiful Design

Whether you’ve got an extensive garden area or just a postage-stamp-sized balcony, you can garden in containers just about anywhere. There are some similarities in techniques for gardening in the landscape versus containers, however there are many key differences for success too. This week’s guest is Karen Chapman, and she’s a sought-after expert in the world of container gardening. Today, she shares some tips and techniques for spectacular, low-maintenance and healthy container gardens.

Originally from England, Karen has owned her own container garden and landscape design business for many years. She’s produced award-winning books and online courses, and she’s a popular speaker as well. I’ve had a chance to review her award-winning online course – Designing Abundant Containers – and I highly recommend it if you have an interest in adding container arrangements to your property.

Fortunately for us, Karen is sharing some of her wisdom here, so let’s get to it.

Karen Chapman is a renowned expert in the world of container garden design, and after seeing examples of her work, it’s easy to understand why. (photo: Andy Chapman)

Choosing the Right Container

There is an overwhelming array of container options out there, and they vary wildly in cost. Size, material, drainage ability – these are all important considerations no matter what you plan to grow. On the other hand, if you’re looking for a container for a decorative arrangement, you’ll also need to bear in mind that what you choose will be as much a part of the design as the plants themselves.

The bottom line is that, if you love the pot on its own – the color, texture and shape – you’ll love it with plants.

That said, don’t be taken in by a beautiful container and overlook that it isn’t an appropriate size. Anticipate how large your edible plants will grow and select a pot which offers the room roots will require to produce. For decorative arrangements, don’t overlook the importance of scale.

Karen gives the example of an arrangement that she created many years ago to place in front of the garage of her three-story home. She happened to view the finished design from across the street and was struck by how ridiculously small the 16” container looked in proportion with the house itself. So, she swapped the plants into a container that was a few feet tall, and the same arrangement of plants went from underwhelming to extraordinary.

Size impacts maintenance needs too. A smaller pot will require more frequent watering, while a large container will be a little more tolerant of neglect.

Another size consideration is vantage point. A container near a door should be tall (or elevated), so you can appreciate the look of the arrangement while standing – instead of looking down at the top of the plants. On the other hand, a shorter pot is perfect for a patio seating area, where the arrangement will be viewed most often from a sitting position.

How much you spend will definitely depend on material. I’ve been impressed with some of the newer plastic pots on the market. I’m not normally a fan of plastic, but these options are affordable, lightweight and can replicate the look of a ceramic container.

There are also some good fiberglass, styrofoam and other synthetic container options which are lightweight and affordable. Karen cautions against using any of these in an area exposed to heavy wind, because they will be more likely to blow over.

The choices at the nursery or big box store can seem overwhelming. Narrow the field with a focus on appropriate size and color along with an understanding of the differences between materials.

Terra cotta pots are sturdy and inexpensive, but they are porous and more likely to absorb water. That makes them susceptible to cracking in cold winter temperatures. Their porous surface also wicks moisture out of the soil, so remember that terra cotta containers will always require more frequent watering.

Metal containers can be beautiful, but they will transfer heat and cold to roots in contact with the interior walls. Extreme temperatures can scorch or frost roots and damage the plants, so it’s a good idea to keep metal containers out of sunny locations. Karen also recommends lining them with bubble wrap (pierced in several areas to allow for water drainage). You won’t see the bubble wrap once the pot is filled, but the plants will appreciate the insulation.

Karen prefers heavy, ceramic pots which are available in a nearly limitless variety of colors and designs. Make no mistake, ceramic pots cost more, but they can be very durable and long-lasting too. Look for frost-resistant options. They are non-porous and less likely to be damaged by cold weather. Frost-resistance won’t always be indicated on the label, but you can ask to speak with the store buyer, who may have additional information on the supplier or manufacturer.

Remember that frost-resistant does not mean frost-proof. Proper precautions should still be taken to prevent cracking.

Always check the clearance of the drainage holes. Don’t allow roots to clog the hole, and don’t set a container with a smooth bottom directly on a smooth patio surface. If water can drain out, there will be less pressure on the pot during freezing temperatures and less risk of roots drowning any time of year.

If you need to raise a container, you’ve got some good options. Pot feet are widely-available and work well, but you might not like the look of them. Another product, pot toes, works the same way but is less visible. Synthetic pot risers are also available, but avoid using those with tall pots which can become unstable.

With proper care, a good container can last for years.

Using Fillers

It’s a long-standing practice to add pebbles, styrofoam peanuts or other filler material to the bottom of a container; but this practice can actually cause harm rather than help your plants.

It’s thought that these create space for water to drain away from plant roots, but instead, they actually raise the water table. I recorded a video demonstration of this in action, so you can see it for yourself. When the water moves through the potting soil and reaches the layer of filler, it slows down and can suffocate plant roots.

Karen recommends against placing a pot shard or other item over the drainage hole too. Roots can wrap themselves around the item and create a drain “plug” that prevents drainage.

This container echoes the hues of the plants it’s holding, and Karen has really packed the plants in to create this abundant look. (photo: Karen Chapman)

We all like to save money, so wanting to use less soil in a large container is understandable. Soil can be expensive. Plus, it can really add to the overall weight of a hefty container. An Ups-A-Daisy is a much better option to save container space for short-lived arrangements of annuals. It creates a false bottom within the pot without inhibiting drainage.

If you’re planting something large and perennial, a false bottom is still not a good idea. Over time, perennial plant roots will need all the space they can get. So, splurge on the soil. You won’t regret it.

Container Soil

Speaking of soil – which product you choose will make a big difference in the health and longevity of your container garden. There are all kinds of options at the nursery and big box stores. It can get overwhelming, but start with products labeled Potting Soil or Container Mix. Don’t use Garden Soil – it’s too dense for a container environment.

Karen plants containers for all four seasons of her Pacific Northwest garden, and she’s never found one product that meets the needs for all times of the year and every type of plant. So, she makes her own. You may have seen my perfect soil recipe for the garden? Well, Karen has her perfect container soil recipe.

She starts with a mix that is peat-based and looks for an option which doesn’t include any water-retentive polymers, fertilizer or compost. Why? So she can add her own to better suit specific plants and seasons.

Karen likes PRO-MIX All Purpose as her base mix. Personally, I like Soil3 or SoilCubed. It’s not actually a potting mix but it’s high-quality, and it has provided great drainage in my containers.

She typically combines 80% of the base with 20% of good quality compost. Pro tip: She saves her own compost for the garden and uses only purchased compost in her containers because it’s less chunky.

If the pot will hold succulents or another variety which prefers drier soil, she reduces the compost to just 5-10% and adds perlite to lighten the mix and reduce water retention. She prefers not to use vermiculite at all because it isn’t as effective at separating soil particles to create tiny pockets of air container plants need.

Whether you’re growing edibles or an ornamental design, quality soil and proper drainage in your containers are just as important as they are in your garden.

Did you know that temperatures need to reach 55 degrees Fahrenheit or above for slow-release fertilizer to be activated? That’s why Karen prefers to buy soil without fertilizer. She doesn’t like paying for something she doesn’t need during cooler months and prefers to add her own when necessary.

For warm month containers, she likes to add Osmocote fertilizer at planting time. Osmocote will release slowly to last for weeks – which works well for Karen because she tends to forget to apply a liquid fertilizer every couple of weeks. To stimulate root production in a fall arrangement which will carry plants through cold winter months, Karen adds bone meal or bulb food during planting.

Sometimes an arrangement starts to fade after several weeks, but Karen needs it to last a few weeks more. In those situations, she likes to use Moo Poo tea (a compost tea) to buy some extra “wow” time. The tea bag soaks in a 5-gallon bucket of water, and Karen uses the liquid for watering or spritzing on leaves as a foliar feed. One application every couple of weeks can stretch plant health through another month or two.

Now, are you wondering why Karen avoids soil products with water-retentive polymers? Well just like fillers, polymers can sometimes cause more harm than benefit, because they don’t know when a plant is too wet. Polymers do such a good job at retaining water that they can hold too much and suffocate roots, especially during periods of rain.

You may not love the idea of using a peat-based soil product as a base, and I get that. Peat isn’t a sustainable material. Coir-based products are a more environmentally responsible choice. However, it’s worth noting that Karen hasn’t compared the performance of coir against peat, so she can’t recommend it will work as well in containers long-term.

If you opt to do a side-by-side comparison of peat-based versus coir-based soil in your container garden, Karen and I would both love to hear about your results. Share your observations in the Comment section below. This is an experiment I may need to try later this year myself.

Container Garden Design

Next comes the really fun part – the design. Maybe you’re keeping things simple and growing edibles, but if you opt to take things to the next level with decorative container gardening, a good-looking design can be tricky. What plants can you use, and how should they be combined? According to Karen, the sky’s the limit, but there are some good rules of thumb to bear in mind before you head for the nursery.

Colorful arrangement of flowers can command attention, but it’s actually better to start with a focus on foliage. Blooms don’t last forever, and you don’t want to wait to enjoy the container until the blooms come either. Instead, look for interesting foliage. Notice what catches your eye among the sea of plants at the store – like interesting stripes, a bright color, or a unique shape.

Karen suggests building a design around a framework of what she calls Spotlight, Highlight and Limelight. She goes into this principle in-depth during her online course, Designing Abundant Containers, but a good example of a Spotlight plant is a Tropicanna Canna lily. It’s got bold, striped leaves; and when you look closely, you begin to see a range of gorgeous colors in the leaves which provide inspiration for Highlight plants to mix with it.

When you focus on foliage, you create a design that looks amazing with or without blooms. The flowers in this arrangement are taking a backseat to the gorgeous pattern and color of the plant foliage which will last all season. (photo: Karen Chapman)

Any plant can work in a container. Think beyond edibles and flowering annuals to trees, landscape shrubs, ground covers – anything. In fact, Karen says ground covers are one of the most under-utilized options for beautiful arrangements. They look great trailing down the side of a pot, and best of all, they’re inexpensive.

Don’t forget to throw in some unexpected element to elevate an arrangement from predictable to extraordinary. Look for something – like a hot pink bloom, silver foliage or unfurling leaves of a fern. That’s your Limelight plant, and it will take the rest of the plants in the arrangement up a notch.

Evergreen plants are gorgeous in container arrangements – especially if you want something to carry a design from one year into the next. Foliage, interesting bark or even plants which produce berries can all create multi-season interest when you think ahead and consider how the plant will develop over time. For example, Karen has used Japanese maples and shrub dogwood (which has deep red branches) in fall and winter designs.

It’s best to create an arrangement around just two or three colors. Too many different colors are overwhelming and will actually be less attractive. So although you should focus on foliage first, don’t lose sight of the color of any eventual blooms and how they will impact the color scheme you’ve got going.

Don’t forget about the color of the pot itself, either. The container color should be echoed by the plants it holds.

As you’re buying, how do you know when you have enough plants – or too many? Karen has a great trick for this. She draws varying sized circles or squares on an inexpensive white, plastic table cloth to represent container size. For example, she’ll draw squares that are 12” wide, 16” wide, and 20” wide.

She stores this template in her car and, during shopping trips, spreads it out on the bottom of the cart. As Karen comes across plants she likes, she sets them onto the template to mimic the design in progress. This gives her a better sense of scale and placement. Even the pros need a little help getting it right.

When you look closely at the tall, dark leaves of the Elephant Ear in the container on the left, you’ll notice the shades of blue and chartreuse which are highlighted by the other plants in these arrangements. (photo: Karen Chapman)

A common mistake in container gardening is using plants of all the same size. Staggered plant sizes create a better effect.

Picture a container which will be placed next to a wall. In that instance, a design should start with a large plant at the back of the pot near the wall. The next layer forward should be medium-sized plants, with small plants further forward and the smallest – or trailing – plants along the front edge.

Plant size will matter long after purchase too, so be sure to look at the plant tag to see how each plant will grow. Plants are inclined to grow up, fill out, mound, or trail – depending on their species. Pay attention to growth habit, and group the plants to complement each growth type rather than create competition for space. As a result, the layered look will keep going as plants keep growing.

Karen also recommends buying two or three more small plants than you think you’ll need. It’s one of her tricks for creating abundant containers. Unlike the garden, where it’s important to provide each plant proper space, ornamental plants in a container can be crowded together.

Ongoing Maintenance

Like me, Karen recommends drip irrigation with automatic timers to maintain proper moisture in container gardens. That way, you can customize the flow and frequency for each arrangement based on the size of the container, sun exposure and plant types.

In the landscape, it’s best to group plants with the same water requirements. That’s known as hydrozoning and it’s an effective method to manage water efficiently and set plants up for success. When it comes to container gardening, you can take a few liberties and mix drought-tolerant plants with thirsty species.

Karen sometimes mixes succulents, like echeveria or kalanchoe which prefer dry conditions, with plants requiring frequent watering. These combinations just require a little more thoughtfulness in management.

If you use drip irrigation, place the emitter away from drought-tolerant varieties by pinning it near the base of the plants requiring more water. Alternatively, you could opt to water by hand in order to target the moisture around the thirsty plants. However, if you really want to control moisture levels within a container, try the pot-in-pot technique. Plant the drought-tolerant plant into a small plastic nursery pot, then sink the plastic pot into the soil of the container arrangement to keep the plastic pot’s soil drier.

These bright colors work together because Karen has kept the palette to three: purple, red and varying shades of green. (photo: Karen Chapman)

If you’ll be away from home for a few days, automated drip irrigation will keep your container garden going strong. I’ve been using Rain Bird® drip irrigation products and automatic timers for several years, and they have saved me through many busy seasons of travel to film for Growing a Greener World®.

You can also help containers get by without water for a few extra days by moving them into a shady spot while you’ll be gone. Don’t be afraid to get creative. Karen has seen homeowners place sun umbrellas over containers to shade them when they can’t be easily moved. I shared more vacation preparation tips in a podcast from last year.

Another question I’m often asked is whether or not container soil can be re-used season after season. The answer depends on a number of factors.

For example in a small container, the soil becomes a mass of roots within a few months, so there’s not much value in reusing it again. Soil from a larger container might be worth re-using – especially if it was high quality at the start – but just like your garden, it could benefit from a soil amendment.

Karen often keeps trees and shrubs in large containers (20” or taller) for five years or more without ever changing their soil. In these instances, she scratches in or tops off the soil surface with fresh compost to re-infuse container with nutrients and organic matter.

How do you know when container soil needs replacement or amending? Just like in the garden, observation is your best guide when working with containers. If plants are just “getting by” rather than thriving, it’s time to repot.

When you prefer to keep plants in the same container, you can remove and root prune them. Then, add fresh soil or amend the existing soil and replant. Root pruning works well on woody plants, shrubs and trees. Herbaceous plants, which don’t respond well to root pruning, can usually be divided.

Multiple Container Arrangements

Hopefully, these techniques provide some solid ideas for your next container arrangements, but what if you want to group containers together? There’s an art to that too.

Each arrangement should look great on its own, but you want the group to look cohesive. Try to group pots with a similar color scheme but of different sizes. For example in a grouping of three containers, Karen recommends that the largest pot contain the most dramatic arrangement. The second pot should be a little more restrained, while the smallest pot should contain just one specimen plant.

Notice how the colors in this container group are cohesive? Although the pot on the right isn’t much larger than the one on the left, Karen has elevated it to create the illusion of staggered size. (photo: Karen Chapman)

Space the pots of the group slightly apart from each other, but pay attention through the season. As the plants contained grow more lush, you may need to space them a little further apart to provide the best effect.

Hopefully, these techniques will help your container gardening in seasons to come, but Karen has even more to share in her online course too, including a video demonstrating how to place plants into a container arrangement. Have you already listened to our conversation? If not, click the Play icon in the green bar under the title at the top of this page. You’ll hear Karen share more examples and a few tips for those times when you need to move larger containers.