LONDON — As the vernal equinox approaches, seasoned gardeners are shifting their focus from winter dormancy to the flurry of March planting. This pivotal window in the horticultural calendar serves a dual purpose: it offers a final opportunity to secure “in the green” spring blossoms while simultaneously initiating the long-term growth of summer-flowering favorites. Experts suggest that decisions made in the dirt this month will dictate the vibrancy of landscape displays from July through the first frosts of autumn.
Navigating the Seasonal Transition
The primary distinction for gardeners to master this month is the timing of “spring bulbs.” While autumn-planted varieties like tulips and daffodils are currently emerging, March is the premier season for planting summer-flowering tubers and corms, including Dahlias, Gladioli, and Cannas.
For those who missed the autumn window for traditional spring flowers, horticulturalists recommend “in the green” planting. By purchasing snowdrops or bluebells while they are actively growing rather than dormant, enthusiasts can successfully establish colonies that would otherwise fail to thrive if planted out of season.
The Heavy Hitters: Dahlias and Gladioli
The Dahlia remains the undisputed centerpiece of the summer garden. In temperate regions, tubers can be placed directly into rich, well-drained soil starting in mid-March. To ensure success, plant them 10–15 centimeters deep and provide ample spacing of up to 90 centimeters to accommodate their substantial mature size. Because Dahlias are heavy feeders and highly sensitive to frost, gardeners should incorporate compost into the planting hole and keep horticultural fleece nearby for emergency insulation.
For architectural height and a steady supply of cut flowers, Gladioli are indispensable. Experts advise planting corms 10 centimeters deep in successive batches every two weeks through May. This staggered approach prevents a singular, short-lived bloom and ensures a continuous vertical display throughout the warmer months.
Exotic Interests and Shade Solutions
Homeowners looking for unique textures are increasingly turning to Eucomis, also known as the Pineapple Lily. This hardy gem thrives against south-facing walls, producing exotic spikes in late summer. Similarly, Crocosmia—particularly the vibrant ‘Lucifer’ cultivar—offers high-impact, fiery hues that serve as a magnet for pollinators.
For the more difficult, shaded corners of the patio, tuberous Begonias offer a solution. Unlike most summer bulbs that crave full sun, Begonias flourish in partial to full shade, making them ideal for hanging baskets and containers.
The Indoor Head Start
In cooler climates, starting tender bulbs indoors is a strategic move to extend the flowering season.
- Cannas: These tropical giants benefit from a 24-hour warm water soak to break dormancy before being potted and kept at temperatures above 18°C.
- Begonias: Tubers should be placed hollow-side up in moist compost and kept in bright light.
- Dahlias: Starting tubers in a frost-free greenhouse in March allows for a robust root system to develop before the final spring frost passes in late May.
Best Practices for Maintenance
Success in the summer garden requires more than just planting; it demands rigorous soil preparation and pest management. High-potassium fertilizers, such as those used for tomatoes, should be applied once foliage is established to prioritize flower production over leaf growth.
Furthermore, gardeners must remain vigilant against spring pests. Emerging shoots are highly vulnerable to slugs and snails, while container-grown Dahlias and Begonias may face threats from vine weevil grubs. Utilizing biological controls like nematodes in the spring can prevent significant underground damage before it reaches the surface. By acting now, gardeners can ensure a resilient, color-coordinated display that persists well into the autumn months.