When To Plant Nasturtium Seeds In Zone 9

If you’re gardening in zone 9, you might be wondering when to plant nasturtium seeds for the best show of flowers and leaves. Getting the timing right is the key to a lush, productive plant, and it’s simpler than you might think. This guide will walk you through the optimal spring and fall planting windows, so you can enjoy these vibrant, edible blooms with minimal fuss.

Nasturtiums are wonderfully adaptable, but they have one major dislike: intense summer heat. In zone 9, our mild winters and long growing seasons are a big advantage. The trick is to plant when temperatures are cool enough for germination but warm enough for steady growth. This gives you two perfect planting seasons each year.

Understanding Your Zone 9 Growing Calendar

Zone 9 is characterized by its long, hot summers and very short, mild frost periods. The first frost typically arrives in late December or even January, and the last frost is often in February or early March. This climate allows for a long growing season, but it also means summer heat can be a major stressor for many plants, including nasturtiums.

Nasturtiums thrive in cooler conditions and will often stop flowering or become leggy during peak summer heat. Therefore, the goal is to time your planting so the plants mature during the pleasant temperatures of late spring or fall.

Optimal Spring Planting Timing

For a glorious spring and early summer display, you’ll want to get your seeds in the ground after the threat of frost has passed but well before the summer furnace kicks in.

Best Window: Late February through mid-March is generally ideal. You can often start even earlier if a warm spell hits.
Soil Temperature: Nasturtium seeds germinate best in soil temperatures between 55°F and 65°F.
The Goal: Planting in this window allows the plants to establish and put on their main floral show in April, May, and early June before the intense summer heat of July and August.

If you get a late cold snap after planting, don’t worry too much. Established seedlings can handle a very light frost, especially if you cover them. Its more the soggy, cold soil that can cause problems with seeds.

Optimal Fall Planting Timing

Fall is arguably the best time to plant nasturtiums in zone 9. The cooling temperatures are perfect for them, and they will often perform even better than spring plantings.

Best Window: Aim for late September through October. In some parts of zone 9, you can push into early November.
Why It Works: The soil is still warm from summer, which aids germination, but the air is cooling down, creating ideal growing conditions.
The Reward: Fall-planted nasturtiums will grow vigorously through the mild winter, often blooming straight through until the heat returns the following summer. They are remarkably resilient to light frosts.

Step-by-Step: How to Plant Your Nasturtium Seeds

Nasturtiums are famously easy to grow from seed, and they prefer to be sown directly in the garden where they will grow. They don’t like having their roots disturbed by transplanting.

Choose the Right Spot: Pick a location with well-draining soil and at least 4-6 hours of sunlight. Too much rich soil or fertilizer will give you lots of leaves but few flowers. They actually bloom better in somewhat poor soil.
Prepare the Soil: Loosen the soil about 8-12 inches deep. If your soil is very heavy clay, mix in some compost or sand to improve drainage. Avoid adding fertilizer.
Plant the Seeds: Plant seeds about 1/2 inch deep and 10-12 inches apart. You can sow them a little closer if you’re using a trailing variety for ground cover. Water the area gently but thoroughly.
Germination: Seeds typically sprout in 7-10 days. Keep the soil lightly moist until you see seedlings emerge.
Thin Seedlings: Once they have a few sets of true leaves, thin them to the proper spacing to ensure good air circulation.

A Note on Seed Preparation

Some gardeners recommend soaking nasturtium seeds overnight in lukewarm water before planting. This can soften the hard seed coat and speed up germination, especially in drier soil. It’s not strictly necessary, but it can give you a slight edge and more uniform sprouting.

Caring for Your Zone 9 Nasturtiums

Once established, nasturtiums require very little care, which is part of there appeal.

Watering: Water regularly when young. Mature plants are somewhat drought-tolerant but will perform best with consistent, moderate watering. Avoid overhead watering to prevent mildew on the leaves.
Feeding: Do not fertilize. As mentioned, rich soil encourages leafy growth at the expense of flowers. If your plants are all leaves and no flowers, the soil is likely too nutrient-rich.
Pests: Nasturtiums are great companion plants because they attract aphids away from your vegetables. Simply check the undersides of leaves regularly and spray off aphids with a strong stream of water if they become too numerous.

Common Problems and Solutions in Zone 9

The main challenges in our climate are heat and humidity.

Summer Heat Stress: Plants may stop blooming, look wilted, or develop yellow leaves. You can cut them back hard in late summer, water deeply, and they will often regrow and bloom again in the fall.
Powdery Mildew: This white fungus on leaves is common in humid or crowded conditions. Ensure proper spacing for air flow, water at the soil level, and remove severely affected leaves. Resistant varieties are also available.
Caterpillars: The caterpillars of cabbage white butterflies love nasturtiums. Hand-pick them off or use an organic BT (Bacillus thuringiensis) spray if damage is severe.

Harvesting Leaves and Flowers

All parts of the nasturtium are edible! The leaves have a peppery, watercress-like flavor, and the flowers are milder and beautiful in salads.

Harvest leaves and flowers in the morning when they are most turgid.
Pick flowers just after they open fully.
Regular harvesting encourages the plant to produce more growth.

FAQ: Nasturtiums in Zone 9

Can I plant nasturtium seeds in summer in zone 9?
It’s not recommended. The extreme heat will likely prevent germination or stress young seedlings so much they won’t thrive. It’s better to wait for the fall window.

Will nasturtiums survive winter in zone 9?
Yes, they often will. Nasturtiums are typically grown as annuals but in zone 9’s mild winters, they frequently behave as short-lived perennials or self-seed readily, coming back on their own the next season.

My nasturtiums are vining but not flowering. What’s wrong?
This is almost always due to excess nitrogen in the soil. This can come from fertilizer or very rich garden soil. Sadly, there’s not a quick fix, but next time, plant them in a less fertile spot.

What are the best nasturtium varieties for zone 9?
All types do well, but for heat tolerance, look for varieties like ‘Alaska’ or ‘Empress of India’. For ground cover, any trailing type is excellent. Dwarf or bush types like ‘Whirlybird’ are great for containers and edges.

Can I start seeds indoors for a head start?
You can, but use biodegradable pots that can be planted directly into the soil to minimize root disturbance. Start them about 2-3 weeks before your intended outdoor planting date.

By following these simple timing guidelines for zone 9, you can enjoy two spectacular seasons of nasturtiums each year. Their bright flowers and tasty leaves are a wonderful, low-maintenance addition to any garden, providing color, flavor, and even pest management benefits. Just remember: avoid the summer heat, skip the fertilizer, and you’ll be rewarded with an abundance of these cheerful plants.