When and How to Start Planting Nasturtium Seeds
Planting nasturtium seeds is a straightforward process, yielding cheerful, prolific blooms and edible leaves and flowers. These annuals are known for their rapid growth and preference for warmer conditions, making them ideal for sowing directly into the soil once the last frost has passed. Alternatively, you can get a head start by sowing them indoors a few weeks prior, though they transplant best when young due to their sensitive taproots.
The ideal time for planting nasturtium seeds outdoors is when the soil has begun to warm up, typically from mid-spring onwards in most climates. Aim for a sunny spot, although nasturtiums tolerate partial shade, which might result in fewer flowers but lush foliage. They are not fussy about soil type, often thriving in poorer conditions, which can even encourage more flowering. Avoid overly rich, heavily fertilised soil, as this can lead to an abundance of leaves at the expense of blooms.
When preparing your planting area, ensure good drainage. Nasturtiums dislike waterlogged roots. If you are sowing directly into the ground, loosen the soil to a depth of about 15-20 cm. For containers or window boxes, use a good quality, well-draining potting mix.
The success of your nasturtium planting hinges on timely sowing and appropriate conditions.
Direct Sowing into Garden Beds
For direct sowing, create shallow drills or individual holes about 2-3 cm deep. Space the seeds approximately 20-30 cm apart. If planting multiple rows, allow about 30-45 cm between them. Gently cover the seeds with soil and water them in lightly. Avoid overwatering, which can wash away the seeds or lead to rot.
Starting Nasturtiums Indoors
If starting indoors, use biodegradable pots or peat pots to minimise root disturbance during transplanting. Sow 1-2 seeds per pot, about 2 cm deep. Keep the pots in a warm location, ideally around 18-24°C. Germination typically occurs within 7-14 days. Once seedlings have a few true leaves and the risk of frost has passed, they can be transplanted into their final positions. Water the biodegradable pots thoroughly before planting to help them break down and reduce transplant shock.
Germination and Early Care for Seedlings
Once planted, nasturtium seeds require consistent moisture but not saturation to germinate effectively. Keep the soil consistently damp but not waterlogged. You should begin to see seedlings emerge within one to two weeks, depending on soil temperature and moisture levels. The cotyledons, or seed leaves, will appear first, followed by the true leaves, which are characteristically round and shield-shaped.
Handle young nasturtium seedlings with care, especially when transplanting. Their long taproots are sensitive to disturbance. If you started them in biodegradable pots, you can plant the entire pot directly into the ground or a larger container. This method significantly reduces the risk of root damage and transplant shock, allowing the plant to establish more quickly.
Ensure that seedlings transplanted outdoors are acclimatised to their new environment beforehand. Gradually expose them to outdoor conditions over a week, starting with a few hours in a sheltered spot and increasing the duration each day. This hardening-off process prepares them for the full sun, wind, and temperature fluctuations of their garden home.
Young nasturtium plants are remarkably resilient, but treating their delicate root system with respect during transplanting is key to vigorous growth.
Feed sparingly, if at all. Nasturtiums perform best in nutrient-poor soil. Excessive feeding, particularly with nitrogen-rich fertilisers, will result in lush, green foliage but disappointingly few flowers. If your soil is particularly poor, a light application of a balanced, low-nitrogen fertiliser once during the growing season might be beneficial, but it is often unnecessary.
Nasturtium Seed Planting: What to Consider Next
After your nasturtium seeds have successfully germinated and established, ongoing care is minimal, allowing you to enjoy their vibrant display and culinary uses. Regular watering is important, especially during dry spells, but allow the soil surface to dry out slightly between waterings. Overwatering can lead to root rot and fewer blooms.
Deadheading spent flowers isn't strictly necessary for nasturtiums, as they tend to be self-cleaning and will continue to produce blooms until the first frost. However, removing faded blooms can sometimes encourage further flowering and keep the plant looking tidy. If you wish to save seeds for next year, allow a few of the best flowers to go to seed. The seeds are ready to harvest when they turn brown and feel firm.
Choosing the Right Variety
Nasturtiums come in a range of varieties, from trailing types perfect for hanging baskets and spilling over walls, to bushy, compact forms ideal for borders and containers. 'Alaska' varieties offer variegated foliage, while 'Jewel' series are more compact and bushy. Consider the growth habit that best suits your garden space and aesthetic goals when selecting which nasturtium seeds to plant.
Companion Planting and Pest Control
Nasturtiums are often lauded for their companion planting benefits. They are thought to deter certain pests, such as aphids and whiteflies, from susceptible plants like brassicas. Conversely, they can act as a trap crop for aphids, drawing them away from more valuable crops. It's also worth noting that nasturtiums themselves can occasionally attract slugs and snails, particularly young seedlings.
Understanding your soil's drainage is paramount for successful nasturtium growth.
While generally robust, nasturtiums can occasionally suffer from fungal diseases like black spot or powdery mildew, especially in humid conditions or if overwatered. Ensuring good air circulation and avoiding overhead watering can help prevent these issues. If pests like aphids do appear, a strong jet of water or insecticidal soap can usually manage them. Companion planting with flowers like marigolds can offer broader pest deterrence.
Understanding Nasturtium Seed Germination Times
The germination period for nasturtium seeds is generally reliable and relatively quick, which is one of the plant’s many appeals. Under optimal conditions, you can expect to see the first signs of life within 7 to 14 days. This timeframe is influenced by several factors, including soil temperature, moisture levels, and seed viability.
Soil temperature is a critical element. Nasturtium seeds germinate best in soil temperatures ranging from 18°C to 24°C. If you are planting outdoors before the soil has adequately warmed up, germination may be slower or less successful. For this reason, sowing directly after the last frost or starting seeds indoors ensures a more favourable temperature environment.
Moisture plays an equally vital role. The soil should be kept consistently moist but not saturated during the germination phase. If the soil dries out completely, the emerging seedlings can perish. Conversely, waterlogged conditions can cause the seeds to rot before they have a chance to sprout. A gentle watering immediately after sowing and maintaining this consistent dampness is the goal.
Factors Affecting Germination Speed
While the 7-14 day window is a good estimate, several variables can affect how quickly your nasturtium seeds germinate. Older seeds may have a lower germination rate and take longer to sprout. The depth at which the seeds are planted is also important; planting them too deep can delay emergence, while planting too shallow may expose them to drying out. Aim for that 2-3 cm depth for optimal results.
When comparing the direct sowing method versus starting seeds indoors, you might notice slight differences in the visible growth timeline. Direct-sown seeds benefit from the ground's natural warmth, but indoor-started seeds are already growing when they reach their final location, potentially giving them an earlier start in overall development. However, the inherent sensitivity of the nasturtium taproot means that indoor starts must be handled with extreme care.
Patience combined with the right conditions is your best approach to successful nasturtium seed germination.
If, after two weeks, you see no sign of germination, it might be worth investigating the conditions. Was the soil warm enough? Was it kept consistently moist? Were the seeds planted at the correct depth? Sometimes, simply ensuring consistent moisture and warmth will prompt germination, even if it takes a few extra days beyond the usual range.