Planting Seeds in March: A Guide for Gardeners
### Sowing and Caring for Half-Hardy and Tender Annuals in March
As spring approaches, it's time to start sowing half-hardy and tender annuals indoors to ensure a bountiful bloom later in the season. Here's a guide on how to sow and care for these plants effectively.
#### Sowing Half-Hardy and Tender Annuals
To sow half-hardy and tender annuals, begin by starting seeds indoors in seed trays or pots filled with seed compost or a light covering of vermiculite. Keep them in a warm place to encourage germination. Some popular half-hardy annuals that benefit from early sowing include osteospermums, which are usually sown indoors between February and April.
For tender annuals like sweet peas, sow seeds indoors in containers between late January and early March, maintaining soil temperatures around 50-55°F (10-13°C) for germination. Half-hardy annuals like marigolds can be started indoors in March or sown directly outdoors once the risk of frost has passed, usually in late spring.
#### Transplanting and Planting Out
Once seedlings develop their first true leaves, prick them out into individual pots to grow on. Plant out tender or half-hardy annuals only after the last frost date in your area (often not until late May or early June), to avoid frost damage. When planting out, ensure the root ball is level with the soil surface, firm in the soil, and water well after planting.
#### Care Instructions
Watering: Keep soil evenly moist but not soggy. Water seedlings regularly until established. Half-hardy annuals in borders can tolerate less frequent watering after establishment; those in containers require more frequent watering in hot weather.
Feeding: Feed weekly during the growing season with a general-purpose plant food to promote continuous flowering.
Pruning and Deadheading: Many half-hardy annuals like Angelonia are self-cleaning and require little or no deadheading; however, cutting back spent spikes or pruning in mid-summer can rejuvenate growth and flowering.
Soil: Use well-draining, fertile soil. Some plants prefer slightly acidic soil (pH 5.5 to 6.2), but good quality seed compost for seedlings is essential.
Protection: Tender plants are sensitive to frost. Overwintering indoors or in a greenhouse is advised if you want to keep them beyond summer, especially for borderline hardy species.
#### Examples of Half-Hardy and Tender Annuals Suitable for March Sowing
| Flower Type | Sowing Time | Planting Out | Notes | |---------------------|------------------------|--------------------|------------------------------------| | Osteospermum | Indoors Feb-April | After last frost | Thrives in full sun, drought tolerant| | Marigolds | Indoors March or direct outside late spring | After last frost | Attract pollinators, deter pests | | Angelonia | Indoors March | After frost danger | Self-cleaning, prune mid-summer | | Sweet Peas | Indoors late Jan-March | As soon as soil workable | Prefers cooler temperatures for growth|
After germination, tomato seedlings should be placed in a well-lit spot to avoid leggy growth and pricked out into individual pots once large enough to handle. Cold frames are useful for warming the soil, hardening off seedlings, growing on young plants, and raising cuttings. An inexpensive cold frame can be made from pallets for the base and an old window for the sloping top.
Morning glory (Ipomoea) adds wonderful color and drama to any planting scheme with its vivid flowers that open early and close up in mid-afternoon. Chives can be sown under cover this month and transplanted to individual pots when seedlings are large enough to handle. Celeriac seeds should be sown under cover in seed trays or modules and germination can take around three weeks. 'Giant Prague' and 'Monarch' are some great celeriac varieties to choose from. Cosmos are popular half-hardy annuals with airy foliage and vibrant daisy-like blooms, suitable for container displays, cottage garden borders, and as a cut flower.
Gardening in March is an excellent time to sow half-hardy annuals like osteospermums and marigolds indoors, while tender annuals such as sweet peas can be started in containers between late January and early March. After germination, these seedlings should be cared for by providing them with adequate light, soil moisture, and nutrients before planting them outdoors, ideally after the last frost date.
