Free Guide to Growing Nasturtium From Seed

Understanding Nasturtium Plants and Why Growing From Seed Makes Sense

Nasturtiums are flowering plants known for their bright, colorful blooms and distinctive round leaves. The name comes from the Latin words meaning "nose" and "twist," referring to the plant's peppery scent and the twisted appearance of its seed pods. These plants are native to Central and South America but grow well in many climates around the world.

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Growing nasturtiums from seed offers several practical advantages over purchasing established plants. Seeds cost significantly less—typically between $2 and $5 per packet containing 10 to 30 seeds, compared to $8 to $15 per starter plant at garden centers. A single seed packet can produce enough plants to fill a garden bed or numerous containers. Additionally, growing from seed gives you more variety choices, as seed catalogs often feature unusual colors and varieties not commonly found in stores.

Nasturtiums serve multiple purposes in gardens. Some gardeners plant them as ornamental flowers in beds and borders. Others use them in containers on patios and balconies. The flowers and leaves are edible with a peppery flavor, making them popular additions to salads. The plants also attract pollinators like bees and butterflies, supporting garden ecosystems. Some gardeners specifically plant nasturtiums to attract aphids away from vegetable plants, using them as "trap crops."

The growing season for nasturtiums is relatively short. From seed to flowering typically takes 6 to 8 weeks, meaning you can see results within a couple of months. This quick timeline appeals to many home gardeners who want visible progress without a long wait.

Practical Takeaway: Starting with seeds is an economical way to get multiple nasturtium plants with variety options and faster results than waiting for seeds to mature naturally.

Selecting and Preparing Nasturtium Seeds for Planting

Nasturtium seeds are among the largest and easiest seeds to handle for home gardeners. Individual seeds measure roughly the size of a pea or small marble, making them simple to plant without special equipment. This size also means you can see exactly what you're planting and control seed spacing easily.

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When purchasing seeds, look for packets dated for the current year. Seed viability—the ability to germinate—decreases over time. Nasturtium seeds stored in cool, dry conditions remain viable for about 2 to 3 years, but fresher seeds have higher germination rates. Reputable seed companies typically print the year on packets. Common nasturtium varieties available include 'Tropaeolum majus' (tall climbing types), 'Tropaeolum minus' (dwarf compact types), and specialty colors ranging from deep crimson to pale yellow to bicolored combinations.

Before planting, some gardeners soak nasturtium seeds in room-temperature water for 12 to 24 hours. This practice can soften the seed coat and potentially improve germination rates, though it's not strictly necessary. If soaking, use a small container and change the water once midway through the soaking period to prevent mold growth.

You may notice nasturtium seeds have a hard outer shell. Lightly scarifying the seed coat—gently scratching it with sandpaper or a file—creates tiny breaks in the surface that allow water to penetrate more easily. This step can improve germination from approximately 60 to 80 percent up to 85 to 95 percent in some cases. Be gentle; you want to roughen the surface without creating deep gouges or damaging the seed inside.

Store unused nasturtium seeds in a cool, dry location. An envelope placed in a plastic container with a silica gel packet works well. A basement, unheated garage, or cool closet maintains the temperature and moisture conditions that preserve seed viability. Avoid warm, humid locations like bathrooms or kitchens where steam and heat fluctuate.

Practical Takeaway: Nasturtium seeds are beginner-friendly due to their size. Soaking and light scarification improve germination rates, and proper storage keeps remaining seeds viable for future seasons.

Creating the Right Growing Environment and Timing Your Planting

Timing nasturtium planting depends on your climate and whether you're starting indoors or direct seeding outdoors. Nasturtiums are tender annuals, meaning frost kills them. They need soil temperatures of at least 50°F to germinate, but germination occurs faster and more reliably in warmer soil between 60°F and 70°F. In most climates, this means planting after the last frost date in spring.

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For direct outdoor seeding, wait until soil has warmed and frost danger has passed. Planting too early in cold, wet soil often results in seed rot rather than germination. You can check soil temperature with an inexpensive soil thermometer available at garden centers for $10 to $20. Push it 3 to 4 inches into the soil in the morning for an accurate reading. Direct seeding typically occurs 1 to 2 weeks after the last spring frost date in your area.

For indoor seed starting, begin 4 to 6 weeks before your last spring frost date. This approach gives you a head start and lets you transplant established seedlings into the garden when conditions are right. Fill seed-starting trays or small pots with sterile seed-starting mix—a lightweight, soil-free medium designed specifically for germinating seeds. Compressed peat pellets, coconut coir blocks, or cell trays all work well. Avoid using garden soil, which can compact and harbor disease organisms.

Plant seeds approximately 1/2 inch deep, placing one seed per cell or small pot. Nasturtium seeds are large enough to plant individually without thinning later. Water gently with a spray bottle to keep the medium consistently moist but not waterlogged. Cover the seed tray with a humidity dome or clear plastic wrap to maintain moisture and warmth.

Place the seed tray in a warm location. A heating mat designed for seed starting maintains soil temperature around 65°F to 75°F. Without a heating mat, a warm windowsill or spot near (but not directly touching) a heat source works. Germination typically occurs within 7 to 10 days when conditions are optimal, though seeds may take up to 3 weeks in cooler conditions.

Practical Takeaway: Plant when soil or starting medium reaches 60°F to 70°F, and use sterile seed-starting mix for indoor starts to prevent disease and ensure reliable germination.

Managing Seedlings From Germination Through Transplanting

Once nasturtium seeds germinate and seedlings emerge, remove the humidity cover immediately. Seedlings need air circulation to prevent fungal diseases like damping-off, which causes seedlings to collapse at the soil line. While the seed-starting medium should stay moist, avoid leaving it waterlogged.

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Nasturtium seedlings grow quickly and need good light. Place them in a sunny window that receives at least 6 hours of direct light daily, or use fluorescent or LED grow lights positioned 2 to 3 inches above the seedlings. Seedlings grown in insufficient light become leggy—tall and spindly with sparse foliage. Rotate trays regularly if using window light to prevent seedlings from leaning toward the light source.

Maintain temperatures between 60°F and 70°F during the seedling stage. Most homes stay within this range, so no special heating is needed after germination. However, avoid placing seedlings in drafts from heating vents or near cold windows at night.

Nasturtium seedlings are ready for their first true leaves—the leaves that look like characteristic nasturtium foliage rather than the initial rounded seed leaves—within 2 to 3 weeks. At this point, they benefit from a diluted liquid fertilizer. Mix a balanced, water-soluble fertilizer like 10-10-10 (nitrogen-phosphorus-potassium) to half strength and apply according to package directions every 2 weeks. This provides nutrients that the sterile seed-starting medium doesn't contain.

Before transplanting outdoors, seedlings need hardening off—gradual acclimation to outdoor conditions. Beginning 7 to 10 days before your intended transplant date, place seedlings outdoors in a sheltered, shaded location for 1 to