Understanding Nasturtium Seed Sowing Times
The question of when to plant nasturtium seeds hinges on your local climate and whether you intend to sow them directly outdoors or start them indoors. Nasturtiums (Tropaeolum majus) are robust, fast-growing annuals that thrive in full sun and well-drained soil. They are not particularly fussy, but timing sowing correctly ensures you avoid the worst of frost damage and can enjoy their cheerful colours and edible foliage throughout the warmer months. Generally, they prefer a warm, frost-free environment for germination and growth.
For those in regions with mild winters or for an early start, sowing seeds indoors can offer a head start of several weeks. This method is particularly beneficial if your growing season is relatively short. The key is to sow them in biodegradable pots, as nasturtiums dislike root disturbance and transplant best when their root ball can be planted directly into the ground. When starting indoors, aim to sow seeds about 3-4 weeks before your last expected frost date.
Direct sowing is often the most straightforward approach, especially given their rapid germination rate and tolerance for being transplanted. The general rule for direct sowing is to wait until all danger of frost has passed and the soil has begun to warm up. This typically falls between mid-spring and early summer, depending on your specific geographical location. Soil temperature is a more reliable indicator than the calendar; aim for soil that is consistently above 15°C (60°F).
- Sow indoors 3-4 weeks before last frost for an early start.
- Direct sow outdoors after all danger of frost has passed.
- Ensure soil is warm, ideally above 15°C, for direct sowing.
- Use biodegradable pots for indoor starts to minimise root disturbance.
Indoor Sowing for an Early Bloom
Starting nasturtium seeds indoors allows you to get ahead of the season, providing blooms and peppery leaves earlier in the year. Use peat pots or other biodegradable containers, as nasturtiums are sensitive to root disturbance. Sow seeds about 2-3 cm deep, one or two per pot. Keep the pots in a warm spot, around 18-21°C, and germination should occur within 7-14 days. Once seedlings have developed a few true leaves and the risk of frost has completely passed in your area, they are ready to be transplanted outdoors. Harden them off for a week beforehand by gradually exposing them to outdoor conditions.
Direct Sowing Outdoors
Directly sowing seeds into the garden bed is often the simplest method. Choose a sunny location with well-draining soil. Nasturtiums are adaptable and can tolerate poorer soils, which often results in fewer leaves and more flowers. Sow seeds at a depth of about 2-3 cm, spacing them 20-30 cm apart for trailing varieties and slightly closer for bush types. Water them in gently and keep the soil consistently moist until germination. Germination typically takes 7-21 days. Nasturtiums can also be succession sown every few weeks until mid-summer to ensure a continuous display of flowers.
Protect young seedlings from slugs and snails, which find the tender young leaves irresistible. A barrier of grit or crushed eggshells around them can help deter these pests.
Timing is Everything: When to Plant Nasturtium Seeds in Your Region
The precise timing for planting nasturtium seeds varies significantly based on your climate zone. In the UK, for instance, indoor sowing typically begins in March or April, with direct sowing commencing from April onwards, once the last frost has safely passed. Gardeners in warmer climates might be able to sow seeds directly outdoors as early as February or March, while those in colder regions may need to wait until May or even June. Always consult your local meteorological data or garden centre advice for the typical last frost date in your specific area. Planting too early outdoors risks disappointing results if unseasonal frosts occur.
Consider the mature size of the variety you are planting. Bush types, like 'Alaska' or 'Whirlybird', are more compact and suitable for containers or smaller garden spaces. Trailing varieties, such as 'Jewel of Africa' or 'Hermine Grang', can spread significantly and are ideal for hanging baskets, wall edges, or spilling over garden walls. Understanding their growth habit helps determine spacing and the best location, which indirectly influences the optimal planting window for maximum coverage and visual impact.
For those in the Southern Hemisphere, the timings are reversed. Indoor sowing would typically occur in August or September, with direct sowing from September through to December. The principle remains the same: avoid frost and ensure the soil is warm enough to support germination and growth.
Factors Influencing Nasturtium Seed Germination
Several environmental factors play a role in the successful germination of nasturtium seeds, beyond just the timing of planting. Understanding these elements can help you optimise your sowing strategy and ensure a healthy start for your plants.
Soil Temperature and Moisture
As mentioned, soil temperature is paramount. Nasturtium seeds require warmth to germinate effectively. Temperatures consistently below 10°C (50°F) will significantly slow down or halt the germination process. Ideal soil temperatures range from 15°C to 25°C (60°F to 77°F). Equally important is consistent moisture. The soil should be kept evenly moist but not waterlogged. Overly wet conditions can lead to seed rot, especially in cooler soils. Once seeds have germinated, they are more tolerant of slight drying out, but regular watering will encourage vigorous growth.
Light and Depth
Nasturtium seeds do not require light to germinate; in fact, they often prefer to be sown in darkness. Covering them with soil to the recommended depth (2-3 cm) is sufficient. Too shallow, and they might dry out; too deep, and they may struggle to reach the surface. The soil itself should be light and free-draining. While nasturtiums tolerate poor soil conditions once established, a rich, well-draining seed compost is beneficial for germination and early seedling development, especially for indoor sowings.
Seed Viability and Storage
The viability of nasturtium seeds can vary. Older seeds may have a lower germination rate. If you are using seeds that are more than a couple of years old, consider sowing a few extra seeds to compensate. Proper storage of seeds is key to maintaining their viability; keep them in a cool, dry place away from direct sunlight. For best results, use fresh seeds from a reputable supplier.
When considering nasturtiums, it's worth noting their resemblance in terms of ease of growth and appeal to other popular annuals. For example, growing sweet peas requires similar attention to sowing times and soil conditions to ensure a spectacular display. Similarly, plants like marigolds and petunias are often sown around the same time, typically after the last frost.
Nasturtiums are forgiving plants, but success hinges on respecting their need for warmth and avoiding the perils of frost.
Common Mistakes to Avoid
One of the most frequent errors is planting too early, exposing young seedlings to late frosts. Another common pitfall is over-watering, particularly when seeds are sown indoors in cool conditions. Overcrowding seeds or seedlings can lead to weaker plants and reduced flowering. Lastly, disturbing the roots excessively during transplanting can set back growth considerably. This is why using biodegradable pots for indoor starts is highly recommended. If you are keen to grow a variety of colourful flowers, understanding when to plant sunflower seeds or when to plant begonia seeds might also be on your agenda, and these often share similar spring planting windows.
Maximising Your Nasturtium Harvest
Once you've successfully sown your nasturtium seeds, a few simple practices can help maximise both the quantity and quality of your blooms and edible leaves throughout the season. Nasturtiums are known for their prolific nature, but a little attention can enhance their performance.
Feeding and Watering
Nasturtiums are not heavy feeders. In fact, over-fertilising, especially with nitrogen-rich fertilisers, can result in lush foliage at the expense of flowers. If your soil is moderately fertile, additional feeding may not be necessary. If you do choose to fertilise, opt for a balanced liquid feed or one slightly higher in phosphorus and potassium, applied sparingly every 4-6 weeks during the growing season. Regular watering is important, especially during dry spells and when plants are establishing or flowering heavily. Aim to water at the base of the plant to avoid wetting the foliage, which can help prevent fungal diseases.
Deadheading and Pruning
While nasturtiums will continue to flower as they mature, occasional deadheading can encourage more blooms and prevent the plant from putting all its energy into seed production too early. Simply pinch off spent flowers at the base of the stem. For trailing varieties that become leggy or overgrown, a light prune can encourage bushier growth and new flowering stems. This can be done mid-season if plants start to look untidy or less productive.
Consider how nasturtiums fit into a broader planting scheme. They make excellent companions for many vegetables, and their peppery leaves and flowers can add a vibrant, edible touch to salads. If you enjoy growing flowers from seed, you might also be interested in planting fuchsia plant varieties or exploring the art of growing sweet peas for their fragrant blooms. While their planting times might differ slightly, the satisfaction of nurturing a plant from seed remains the same.
Pest and Disease Management
The most common pest affecting nasturtiums is the aphid, which tends to cluster on the undersides of leaves and on young shoots. A strong jet of water can often dislodge them, or you can use an insecticidal soap. Slugs and snails are also fond of young nasturtium plants, as mentioned earlier. Fungal diseases like powdery mildew can occur, especially in humid conditions or when plants are overcrowded. Ensuring good air circulation, watering at the base, and avoiding overly damp conditions can help prevent this. Planting nasturtiums in a sunny spot also aids in drying foliage quickly.
The 'King's Ransom' variety, for example, offers a beautiful blend of yellow flowers and variegated foliage, thriving when planted in accordance with the optimal timings discussed. Its growth habit makes it a versatile choice for borders or containers, provided it receives adequate sunlight.
Encourage branching on bush varieties by pinching out the growing tip when the plant is young, just a few inches tall. This encourages a more compact, floriferous plant.
Harvesting Edible Parts
Both the flowers and leaves of nasturtiums are edible and possess a distinctive peppery flavour, akin to watercress. The flowers are best harvested when fully open, while the leaves are most tender when young. Harvest them regularly to encourage further growth. They can be added to salads, garnishes, or used in herbal remedies. For the best flavour, harvest in the morning after the dew has dried.
Nasturtium Alternatives and Companion Planting
While nasturtiums are wonderfully easy and rewarding to grow, understanding their place in the garden alongside other plants can enhance both aesthetics and pest control. Exploring alternatives and companion planting options can lead to even more successful gardening.
Companion Planting Benefits
Nasturtiums are renowned for their ability to act as a trap crop for certain pests, particularly aphids and some beetles. Planting them near susceptible crops like brassicas (cabbage, broccoli) can draw these pests away from your vegetables. Their vibrant colours also add visual appeal to vegetable patches. Other flowers that share similar planting windows and offer companion benefits include marigolds, which are known for deterring nematodes and other soil-borne pests.
Growing Alongside Other Annuals
When planning your flower beds, consider how nasturtiums complement other popular annuals. Their trailing or mounding habit works well with upright plants. For instance, a mix of nasturtiums with petunias or salvias creates a colourful, layered display. If you're interested in growing tall, striking flowers, learning when to plant sunflower seeds offers another rewarding experience, with sunflowers often planted directly outdoors in late spring once the soil is warm, similar to nasturtiums.
Considering Other Edible Flowers
If the edible aspect of nasturtiums appeals, there are other delightful options. Pansies, violas, and calendula flowers are also edible and can be grown from seed, often requiring similar sowing conditions to nasturtiums – starting indoors in early spring or directly outdoors after the last frost. Each offers a unique flavour and visual appeal for culinary use. The peppery kick of nasturtiums, however, is quite distinct.
When comparing nasturtiums to other flowering plants, consider their light requirements. While nasturtiums prefer full sun, some plants, like begonias or fuchsia plants, can tolerate or even prefer partial shade. This distinction is important for garden design and ensuring optimal growth conditions for all your chosen species. For example, a shady border might be better suited to fuchsias, while a sunny spot is ideal for nasturtiums.
When to Plant Sweet Peas
If you are drawn to the idea of fragrant, beautiful blooms from seed, growing sweet peas is another excellent choice. The timing for planting sweet peas differs slightly from nasturtiums. For the best results, sweet peas are often sown in autumn in milder climates to establish strong root systems, or sown indoors in late winter (February/March) for transplanting out in early spring. This allows them to flower earlier and more prolifically than if sown directly in spring. While nasturtiums are direct sown after frost, sweet peas benefit from an earlier start, often before the last frost has fully passed.
Choosing the right seeds and planting them at the correct time ensures a garden filled with colour, fragrance, and flavour. Whether you are planting nasturtium seeds, sunflower seeds, or sweet peas, understanding the specific needs of each plant is key to a flourishing display.