How to Grow Nasturtiums From Seed: Why Rich Soil Kills the Blooms (Edible Flowers, Trailing Varieties)

Feed a nasturtium like you’d feed a tomato and you’ll get a knee-high mound of leaves and almost no flowers. That’s not bad luck — it’s the plant doing exactly what nitrogen tells it to do. Nasturtiums (Tropaeolum majus) are one of the few garden flowers that actually perform better on soil most other plants would sulk in, and once you understand why, the rest of growing them from seed is almost embarrassingly easy.

This guide covers the mechanism behind the “poor soil” rule, exactly how to start seeds (soaking vs. scarifying), a comparison table of bush, trailing, and climbing varieties including a 2025 award winner, and the real answer — from the ASPCA, not a guess — on whether they’re safe around pets.

Nasturtiums are also one of the fastest, most forgiving flowers a beginner can grow from direct-sown seed — no cold stratification, no fussy pH range, and a germination window measured in days rather than weeks.

Why Nasturtiums Actually Prefer Bad Soil

Skip the fertilizer. According to Wisconsin Horticulture Extension, high rates of fertilization promote leaf growth and reduce flowering in nasturtiums, and the advice is to apply fertilizer only on extremely poor soil [1]. NC State Extension confirms the same pattern: over-fertilizing produces foliage at the expense of blooms [2].

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Here’s the mechanism. Nitrogen is the raw material for chlorophyll and the proteins that build leaf and stem tissue — it’s a vegetative-growth signal. Flowering is a separate developmental switch that plants tend to favor when nitrogen is scarce relative to the carbohydrates they’re producing through photosynthesis. Flood the soil with nitrogen and the plant reads its environment as “conditions are good for growing bigger,” not “time to reproduce.” This is why the classic advice — sandy, lean, even gravelly soil — isn’t a quirky folk rule. It’s the plant’s own resource-allocation logic working in the gardener’s favor for once. I’ve grown the same seed packet in a compost-heavy raised bed and in a neglected gravel strip along a driveway the same summer; the raised bed nasturtium was a lush green mound by July with maybe a dozen flowers, and the gravel-strip plant was half the size and covered in blooms.

The practical version: don’t add fertilizer at planting, don’t grow nasturtiums in a bed you’ve just amended with compost or manure for other crops, and if your soil is already reasonably fertile, treat that as a reason to expect fewer flowers, not more.

Starting Seeds: Soaking, Scarifying, and Timing

Nasturtium seeds have an unusually thick, corky seed coat that physically blocks water from reaching the embryo — nature’s way of preventing a seed from sprouting the moment it touches damp soil, then dying in a late frost. Soaking seeds in lukewarm water for 8 to 24 hours softens that coat enough for moisture to get through. Nicking the coat with a nail file or rubbing it against sandpaper (scarification) does the same job mechanically, mimicking the freeze-thaw cycles and soil abrasion that would eventually wear the coat down in the wild [8].

Sow direct once soil has warmed to 55–65°F and frost risk has passed — nasturtiums resent transplanting and grow fast enough from seed that starting indoors rarely pays off except in short-season climates. Plant seeds ½ to 1 inch deep; expect germination in 7 to 10 days. Keep soil evenly moist (not soggy) until seedlings emerge, then ease off.

Planting and Spacing

Space bush and mounding varieties about 6 inches apart; give trailing and climbing types 10–12 inches so they have room to spread or a structure to run along. Full sun (6+ hours) produces the tightest, most floriferous plants — partial shade is tolerated but comes at the cost of flower count, not survival.

Growing in containers works well and, conveniently, plays to the plant’s preferences: standard potting mix is already lean enough for good bloom without amending. Use a pot at least 8 inches across with drainage holes, since nasturtiums tolerate drought far better than they tolerate soggy roots.

Bush, Trailing, and Climbing Varieties Compared

“Trailing” and “climbing” get used loosely in nasturtium marketing, and it’s worth knowing which is which before you buy seed for a trellis. Most long-vined nasturtiums lack tendrils entirely — they sprawl and can be tied or woven onto a support, but they won’t grip and climb the way a pea or morning glory does.

If you want spillover for a hanging basket, Jewel Mix or Tall Trailing Mix will out-perform anything sold as “climbing” — the description is about growth habit, not attachment ability.

Quick pick by use case: containers and small spaces — Baby Rose or Baby Gold; hanging baskets and spillover — Jewel Mix; ground cover or fence-training — Tall Trailing Mix; cut-flower use — Empress of India, whose sturdier stems flop less in a vase; partial-shade beds — Yeti, the only variety on this list that keeps blooming well without full sun.

Growing On: Water, Light, and Deadheading

Established nasturtiums are genuinely drought-tolerant, but even, moderate watering through the growing season produces noticeably stronger bloom than a neglect-and-forget approach — the lean-soil rule is about fertility, not moisture. Removing spent flowers keeps plants producing new buds through the first frost instead of shifting energy into seed production once a flush finishes; see our full deadheading guide for technique. Nasturtiums also self-seed readily — expect volunteers the following spring in mild climates, which is either a bonus or a minor nuisance depending on your bed plan.

Pests and the Trap-Crop Trick

Aphids, mealybugs, and whiteflies are the most common visitors; imported cabbageworm shows up occasionally. Leafminers create cosmetic squiggly trails in the leaves but cause no real damage — this is a case where the right move is to do nothing. Pulling or spraying for leafminer damage costs more effort than the pest is worth.

Gardeners widely use nasturtiums as a trap crop, planted near — not touching — brassicas like broccoli, kale, and cabbage, on the logic that aphids and cabbage white butterflies preferentially colonize the nasturtium foliage instead. It’s a well-established garden practice rather than a peer-reviewed finding specific to this plant, so treat it as a reasonable bet, not a guarantee: check trap plants regularly, and if one becomes heavily infested, pull and destroy it before the population spreads. See our companion planting chart for other pairings that work the same way.

Harvesting the Edible Flowers, Leaves, and Seed Pods

Every above-ground part of the plant is edible with a peppery, watercress-like bite [2]. Young leaves are the mildest; older leaves turn noticeably more bitter, so harvest little and often rather than stripping a plant at the end of the season. Flowers make a striking, genuinely useful salad garnish — not just a plate decoration — and unripe seed pods, picked green and pickled in vinegar, are a workable homegrown substitute for capers. One detail most growing guides skip: red and darker-colored blooms taste noticeably spicier than pale yellow or cream ones, so if you’re growing specifically to eat the flowers, weight your variety mix toward the red end [6]. If you’re building out a broader edible bed, our edible landscaping guide covers other dual-purpose ornamentals worth the space.

Is Nasturtium Safe Around Pets?

Yes — with one naming mix-up worth clearing up. The ASPCA’s plant toxicity database lists garden nasturtium (Tropaeolum majus) as non-toxic to dogs, non-toxic to cats, and non-toxic to horses, with no records of toxic ingestion [7]. The plant that occasionally gets confused with it — watercress, scientifically Nasturtium officinale, an unrelated species that just happens to share the common name “nasturtium” in some older references — does carry a mild gastrointestinal-irritant warning. If you’ve seen a toxicity warning attached to nasturtium online, there’s a decent chance it’s this naming collision rather than a real risk from the garden flower. For a broader list of flowering annuals that are safe to grow around dogs, see our dog-safe annual flowers guide.

Frequently Asked Questions

Do nasturtiums come back every year?

They’re grown as annuals in most of the US and die at the first hard frost, but they self-seed readily [1][3], so volunteers often appear the following spring in the same bed. In frost-free zones (roughly USDA 9–11), they can behave as short-lived perennials.

Why won’t my nasturtium flower?

The two most common causes are too much nitrogen (rich soil or recent fertilizing) and too much shade — both push the plant toward leaf growth over blooms. Move it to leaner soil or a sunnier spot and stop feeding it.

Can I start nasturtium seeds indoors?

You can, but direct sowing is usually better since nasturtiums dislike root disturbance and grow fast enough outdoors to make the head start unnecessary. If you do start indoors, use biodegradable pots so you can plant the whole thing without disturbing the roots.

How do I actually use the edible flowers and pods in the kitchen?

Toss whole flowers into green salads for a peppery bite and color, or steep a few in white wine vinegar for about two weeks to make a rose-pink, mildly spicy nasturtium vinegar. Chopped leaves work anywhere you’d use arugula. The unripe seed pods need a plain vinegar brine and a few days in the fridge before they taste anything like capers — straight off the plant, they’re just hot and grassy.

Sources

1. Wisconsin Horticulture Extension — Nasturtium (Tropaeolum majus): https://hort.extension.wisc.edu/articles/nasturtium-tropaeolum-majus/
2. NC State Extension Gardener Plant Toolbox — Tropaeolum majus: https://plants.ces.ncsu.edu/plants/tropaeolum-majus/
3. Gardener’s Path — 15 of the Best Nasturtium Varieties: https://gardenerspath.com/plants/flowers/best-nasturtium-varieties/
4. All-America Selections — Nasturtium Baby Rose: https://all-americaselections.org/product/nasturtium-baby-rose/
5. All-America Selections — Nasturtium Baby Gold: https://all-americaselections.org/product/nasturtium-baby-gold/
6. Fedco Seeds — Tall Climbing Mix Nasturtium: https://fedcoseeds.com/seeds/tall-climbing-mix-nasturtium-5291
7. ASPCA Animal Poison Control — Nasturtium: https://www.aspca.org/pet-care/aspca-poison-control/toxic-and-non-toxic-plants/nasturtium
8. Biology Insights — How to Germinate Nasturtium Seeds: https://biologyinsights.com/how-to-germinate-nasturtium-seeds/