As Colorado weather heats up, it’s time for gardeners — especially those with constrained spaces — to fill those pots and planters.

Local experts and garden designers have a lot of advice to offer about making the most of container gardening. It’s great for small spaces, apartment/condo living, patios, and those with limited mobility as containers can be raised up, set on table tops or hung from ceilings. You can add your own flair and creativity, or purchase pre-planted containers if you’re not a DIY person.

You can mix together perennials, annual flowers, herbs, vegetables, ornamental grasses, and even small shrubs.

Containers are truly the option for all levels of gardeners, from beginner to advanced.

Container gardening materials

First, gather your supplies, i.e., planters of any kind, and potting soil mix. For growing larger vegetables (tomatoes, peppers, eggplant, etc.) use at least a 5-gallon container. Smaller vegetables (lettuce, herbs, radishes) can go in 1- to 3-gallon containers. The size ensures there’s enough root space and water-holding capacity. To add in climbing vines, place a trellis support when you plant.

With potting mixes, general guidelines suggest not reusing old soil due to potential disease, overwintered pests, and nutrient depletion. With daily watering, potted mixes do lose their nutrients. You may need to add minerals like phosphorus (great for tomatoes) or potassium (for flowers), depending on what gets potted.

I reuse soil because of the expense and reducing waste. I take out the old soil and mix it with some new compost or soil to reintroduce good microorganisms. I also add in earthworm casting fertilizer.

Plant selection can include transplants or directly growing from seed. I prefer combining food and flowers, which attracts pollinators and enhances your tastebuds. Consider vegetables for containers that are labeled dwarf or patio varieties, such as those recommended in PlantTalk. And mix in different herbs like parsley, basil or cilantro, or even tea-making options like chamomile.

The foundation of plant design for containers

Here’s the fun part. In selecting plant combinations, there are a few ways to approach design. There is the need to consider plants with similar water and sun needs as well as which ones make good companions for one other. The more creative flair with container gardening is based on dimension, shape and color.

The “thriller, filler, spiller” method typically uses three types of plants. It centers on a vertical placement, then filler around that, and finally adding in a spiller, something that flows over the edges. You can watch a video from Proven Winners on creating a container using this method.

For inspiration from a few CSU-Denver master gardeners, check out this pandemic virtual tour.

Tips to mixing vegetables and flowers in containers

The container gardens of Sheila Schultz ather Denver home. These are containers with tomatoes, rhubarb, and herbs.
Gardener Sheila Schultz has planted tomatoes, rhubarb and herbs.

Hannah Lucey, the greenhouse manager at City Floral, suggests pairing pest deterrents and pollinator attractants together with vegetables in containers. For example, tomatoes and marigolds are common companions, but she recommends also adding lemongrass, citronella-scented geraniums, and different salvias for additional benefit.

More proactive pest management comes with adding alyssum, nasturtium and zinnia as trap crops for pests such as aphids, according to Elisa Mack with Auntie M’s Garden, a kitchen garden-design business.

Brad Kuhn, owner of Finding Nectar Nursery in Arvada, suggests planting bloomers that are early and all-season to support pollinators coming to your containers. By having all-season blooms, your containers will attract bees that prefer consistency and routine in their foraging. By letting pollinators know to visit your pots all season long, gardeners ensure they will pollinate your vegetables, thus giving you a higher yield. Win-win.

Some container recommendations from Kuhn: black-eyed Susans, asters, columbines and even milkweed can help make up for biodiversity loss.

Keeping with the “thriller, filler, spiller” method, based on Brad’s recommendations, a pollinator container might have anise hyssops, which are a hummingbird’s favorite; blanket flowers for filler like a yellow-red daisy-like bloom; and then creeping thyme around the edge for scent and small flowers that support butterflies and bees.

A few top mistakes with container planting

The biggest mistakes in container gardening come at the design and planting stage. Of course, once planted, the location placement of your containers matters given Colorado’s intense sun. Containers get hotter and dryer faster, so water daily, preferably in the morning to minimize water evaporation, and monitor shade needs.

Here’s what experts say are the mistakes they see most often:

  • “Planting too deep,” says Hannah Lucey at City Floral. “Not filling the soil high enough to begin with. And planting too many plants where they ‘overflow’ the pot and not leaving a reservoir for watering.”
  • Elisa Mack with Auntie M’s Garden says the biggest mistake she sees is “filling the bottom portions with rocks, plastic jugs or other fillers. It’s actually counterintuitive since the water hits the filler and saturates the bottom of the soil anyway. All you’re doing is shortening the area in which your roots can grow.”
  • Brad Kuhn at Finding Nectar Nursery says three to four hours of direct sunlight is considered full-sun, so location and sun time matter. Also, when planting for pollinators, drainage is the top consistent issue because many native and pollinator plants do not want wet feet. For example, lavender is lovely here in Colorado but is more like a succulent with water needs.

And even if you do make mistakes, one of the great things about container gardening is that you can change your planter if it does not work or you want to add different colors or vegetables.

Have fun designing your garden containers and remember to support our local pollinators.

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