Yellow and white primroses paired with pink hellebores make a pretty spring container garden. (Garden Making photo)
Your spring garden containers don’t always need to include tulips and daffodils for a pop of colour. Many spring-blooming perennials hold up for weeks in a pot display, and can transplanted at the end of the season to make room for summer flowers.
Here’s an 18-inch (45-cm) diameter concrete container beside a neighbour’s front porch filled with lemon yellow Himalayan primroses (Primula florindae), double white primroses (P. vulgaris) and dusty rose hellebores (Helleborus hybrids).
Pink and yellow aren’t always a popular pairing, but these were soft pastel shades balanced with clean white blooms, providing a fresh look for a spring container garden. A bonus was the attractive foliage on the primroses and hellebores.
Once the plants finish blooming, the root balls could be carefully teased apart and transplanted into the garden, where they would flower again next spring.
Evergreens are better prepared to tolerate late spring frosts — even snow — but the flower buds on deciduous trees might not fare as well.
After a hard winter, the last thing you want is to lose plants to a late spring frost. Knowing how to provide frost protection for plants is your first defence.
Simply put, most light frost is frozen dew. It forms on vegetative surfaces and can damage the cells of plants that are actively growing. These include emerging and transplanted perennials, newly planted vegetables, and shrubs and trees leafing out and flowering.
It’s difficult to imagine how a tree hardy enough to withstand wintry weather can be damaged by a little spring frost. Plants prepare for winter by accumulating sugars and certain amino acids that act like antifreeze in their cells, drying tissues to make them more cold resistant. Once warm spring weather arrives, plant tissues begin to absorb water, becoming succulent again. This tender growth freezes at higher temperatures than does dormant tissue, making it more susceptible to frost damage.
Full morning sunlight causes most damage. Light frost freezes the cells just enough to injure the membrane, but not kill the cells. If the plants have an opportunity to repair that damage before they receive full sunlight, the damage will be minimized. That’s why it’s important to shade plants from strong morning sun if frost strikes at night.
Unfortunately, flower buds are more vulnerable to frost than other vegetative growth, so try to site early-flowering trees and shrubs on a northeastern-facing slope where they won’t be vulnerable to the huge temperature swings that occur under harsher, southwestern exposures.
Frost tolerance varies from plant to plant, too. Peas, onions, spinach and lettuce, for example, are better adapted to cooler conditions than are tender crops such as beans, squash, corn and tomatoes, which can be damaged even by temperatures as high as 10° C if sustained for more than two hours. The difference is in the chemical composition of the cell membranes: variations in sugar levels and cell structure can affect a plant’s ability to withstand frosts or cold weather. That’s why gardeners shouldn’t worry about the early appearance of spring bulbs like crocuses, winter aconite, species tulips and some daffodils — these have good frost resistance.
If frost threatens, there are several ways to provide frost protections for plants.
Row covers provide a thermal buffer, just like a blanket. Depending on their thickness (medium-weight versions are best for spring), they can raise temperatures by as much as 4°C. Keep the fabric from touching plants, as this can lower surface temperatures. Row covers allow sun, water and air to permeate and may be left on during the day.
Polytunnels act much like row covers, and the plastic can be stretched over hoops to protect tender crops. Be sure to raise the sides for ventilation during the day to prevent disease caused by warmer temperatures and increased humidity.
To reduce heat loss, apply a mulch of straw, tar paper or newspapers in the evening, before frost occurs, to trap the heat in the soil and plants. Or, cover plants with cardboard boxes or old bed sheets; place rocks or bricks on top of the boxes and on the corners of the sheets to keep coverings in place. Remove coverings and mulch when the threat of frost has passed.
A cold frame — a bottomless box with a clear cover that sits on the ground — is a versatile season extender, protecting tender plants from frost and cold in spring and fall. It can also be used to harden off seedlings started indoors so they slowly acclimatize to the cold. Raise the lid during the day for ventilation.
Cloches, whether homemade from plastic bottles with their bottoms cut off or store-bought glass ones, act as mini-greenhouses for individual plants that need coddling against the cold. Remove cloches in the morning.
Mist plants overnight. As water freezes, it gives off heat, raising the surrounding air temperature. In the morning, turn off the mister once the ice melts from plant surfaces.
Know your last expected spring frost date. The most recent data is the Canadian Climate Normals, 1981 to 2010, published by the federal government online. You can search for your location and click on the tab for climate normals.
This map from 1981 shows the ranges of the average frost-free days in Canada.
Choose containers that are practical and suit your garden style. (Garden Making photo)
Even before you think about what plants you’ll grow in your container garden, consider what garden pots you have on hand, what needs replacing and what you need to acquire.
Almost anything that holds soil and water will work as a container for plants, but consider practicalities and aesthetics, too. The larger the container, the more room there is for a beautiful display of plants, a well as the soil and water needed to keep them thriving. When in doubt, go big. Large containers have more visual impact in the landscape.
When considering materials, keep in mind the weight of a container once it’s filled — moist potting soil is heavy. If you’re creating a potscape above ground level, make sure your balcony can tolerate the weight load. Plastic and fiberglass are lighter than wood and concrete, but dark-coloured plastic heats up in the sun. Some plants don’t like to have their roots cooked. Terra-cotta pots are classic beauties and allow a healthy exchange of oxygen around roots, but they do dry out more quickly than containers made of more solid materials. Concrete is practical and frost-resistant, but heavy. They’re perfect for large containers that will stay in place year-round.
Regardless of what container you use, make sure it has a drainage hole. Don’t cover it with potshards or gravel. (Garden Making photo)
Whatever you choose, make sure there is a drainage hole at the bottom. When watering a container, it’s important to make sure water reaches the very bottom, otherwise roots will grow in just the top few inches. However, any excess water needs to have a way to drain away to ensure plant roots don’t rot. Covering the holes with potshards or gravel is a bad idea — it impedes drainage, rather than improving it. Potshards and gravel also take up valuable space needed for soil and root growth — both of which help plants reach their full potential. Place a square of window screening or a coffee filter over the hole before filling with potting soil to keep the soil in and allow excess water to escape.
Then there are the myriad household items that can be repurposed for container gardens — colanders, baskets, old boots, whatever. Some may need a clear plastic lining to be practical. Be sure to puncture a few holes in the bottom for that all-important drainage and trim off the top edge to just below the top of your container.
As far as aesthetics go, it’s your garden, so choose what makes you and your plants happy. However, by limiting the different kinds of container materials and design styles, you’ll create a more unified, cohesive look.
Track the blooms in your garden using the Bloom Chart.
The Garden Making bloom chart will help you keep track of when plants in your garden are in flower, showing you when there are gaps in bloom. It can be an important tool in achieving succession of bloom in your garden design. Using a bloom chart for individual areas will also be a help in colour design, allowing you to better plan beds devoted to monochromatic schemes, such as white or mauve sections of the garden, or more intricate combinations of pink, lavender and silver, for example.
The bloom chart provides places for you to write in plant names down the right side and columns for the weeks in spring, summer and fall months are listed across the top. First, list the flowering trees, shrubs, perennials, vines and bulbs you already have. Gather any memories, photos and notes you have, because this initial survey will be your key to starting a record of flowering schedules.
As each plant begins to flower, mark the weeks it’s in bloom on the chart. For example, if daffodils begin to bloom the second week of April and last until the second week in May; check off those four corresponding boxes on the chart, next to the entry for daffodils.
Your plant survey and the resulting master list not only shows what specimens you have growing and when they flower, it also reveals the time periods when there’s nothing in bloom. Once the bloom-time chart is filled in, it will be possible to pinpoint short periods of time when nothing is in bloom; for instance, the first 10 days of October, when there’s a slight gap as chrysanthemums fade and late black-leaved cimicifuga isn’t quite out. To bridge that gap will be a research challenge. Plant encyclopedias, good nursery catalogues and Internet sources list the bloom times for perennials and these resources will help you decide on plants to add next year to fill in the gaps.
When using reference materials, remember to factor in your hardiness zone, both in plant selections and in bloom-time adjustment. Perennials adapt to seasonal temperatures, coming into flower earlier in warmer zones (Zones 5 and 6), and later in Zone 4 and lower. In colder zones, winter conditions stay later in spring and hard frost comes earlier in autumn, shortening the growing season.
With good record keeping and careful research, you can achieve a full succession of bloom in just a couple of growing seasons.
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Tuberous begonias such as ‘Nell Gwynn’ are easy to grow. (Photos by Dugald Cameron)
When you consider that tuberous begonias can flower continuously from June until frost, have blooms that last more than a week, are easy to grow, and come in just about every colour, it’s a wonder more gardeners don’t grow them.
If this is your year to try growing tuberous begonias, now is the time to get them started.
Bulb basics
The neat thing about any flower bulb is that it’s a complete flowering kit with food and flower in a durable package (bulb). This food can be delicious, and if you have any bulbs like potatoes, onions, garlic or ginger root, you know what I mean. The begonias we’re discussing grow from concave-shaped tubers. They like a barely moist soil and bright, dappled shade.
A begonia tuber compared to a Loonie coin.
Since tuberous begonias flower non-stop, the sooner you get them going, the sooner (and longer) they’ll start blooming. Use shallow trays or pots, and plant the tubers concave side up in well-draining potting soil. Cover the bulbs with no more than one-half inch (1 cm) of soil.
Potting begonias is a simple process.
Begonia tubers can take awhile to wake up from their winter dormancy, so be patient (an essential virtue every gardener needs). Once they’ve produced leaves, you can transfer them to their final containers.
The minimum pot size for a single tuber is six inches (15 cm) in diameter or three in a 12-inch (30-cm) pot. Some of you may want to plant them directly in the garden, which is fine provided you remember to lift them and bring them indoors before a hard frost. It’s simpler to pot them in terra-cotta pots and plunge the pots in your flower beds, lifting them — pot and all — before winter. Tubers can last for many years if you overwinter them indoors.
Tuberous begonias hate heat, so place them in bright, dappled shade, in morning sun or anywhere where they won’t get baked by midday sun. Their fleshy stems can be fragile in the wind.
Soil for potted bulbs
Why buy potting soil when you can make your own? I mix equal parts peat moss (or coir), well-rotted manure and coarse sand (the kind used to make cement). This provides the food, moisture retention and drainage summer-flowering bulbs like. You’ll know if your bulb is happy if it’s larger at the end of the season than it was at the start.