The Cut-Flower Gardener's Guide to Growing Tall Zinnias
This year, I grew a 7-foot tall zinnia wall in a 3-foot wide by 13-foot long raised garden bed. It was absolutely stunning, and I'm sharing exactly how I did it so you can create your own zinnia wall at home.
Growing Conditions
Growing Zone: 5b-6a (Denver Metro Area, Colorado)
Soil
My garden bed is built with layered branches, lawn clippings, leaves, homemade compost, native topsoil, lawn removal sod, and OMRI-certified organic compost from A1 Organics. This layered approach creates rich, well-draining soil that zinnias love.
Sun Exposure
The bed receives 7-8 hours of direct sun with eastern, southern, and western exposure. Zinnias are sun-lovers, so aim for at least 6-8 hours of direct sunlight.
Watering Schedule
Weeks 1-4: Drip irrigation for 30 minutes daily, plus hand watering as needed to keep soil moist while seeds germinate.
Weeks 5+: Drip irrigation for 30 minutes every other day.
Note: During heat waves (multiple days over 100°F), I supplemented with hand watering whenever the flowers looked droopy.
Pest Management
I don't use pesticides or herbicides. If pests become an issue, I protect the flowers with insect netting or organza bags as needed.
Month-by-Month Timeline
April: Starting Seeds Indoors
I started some zinnia seeds in seed-starting trays under grow lights in my basement. I used heat mats for the first two weeks, then transferred the trays to grow lights only until they were ready to move outside.
Lesson learned: Going forward, I won't start zinnia seeds indoors at all. The transplants took longer to establish and actually flowered later than the seeds I direct-sowed. Save yourself the effort and direct sow instead!
May: Hardening Off & Planting
My last frost date was around May 10th. One week before transplanting, I started hardening off my seedlings by placing them outside during the day and in the garage overnight to acclimate to temperature changes.
To prep the garden bed, I topped it with fresh compost and enabled the drip irrigation system.
When it was time to plant, I planted everything at once—both direct-sowing seeds and transplanting seedlings. I kept the top of the soil consistently moist for seed germination. For the first week, I covered the bed with frost cloth to protect seedlings on cold nights.
June: Trellising & Pinching
When seedlings reached around 14 inches tall, I added trellis netting by anchoring it to garden bed posts and my arbor. I installed two layers of netting:
First layer: approximately 14 inches above the bed
Second layer: approximately 30 inches above the bed
In hindsight, I should have added a third layer at 48 inches for even better support.
The pinching technique: When zinnia stems reached 16-18 inches tall, I cut each stem back down to around 14 inches (just above the first layer of netting). This encourages the stem to thicken at the bottom and branch out, creating multiple blooms at different heights.
As the zinnias grew taller, I continued redirecting any stems that fell out of the netting or grew through the wrong spaces, keeping them growing straight up since they naturally want to grow sideways.
First bloom: June 25th!
July & August: Maintaining & Harvesting
Continue threading zinnia stems back into the trellis net spaces by hand as they grow outward. By July, the trellis netting was completely hidden by foliage when viewed from the side.
Once stems are mature and long enough, start enjoying them as cut flowers. The great thing about zinnias is that the more you cut them, the more they bloom!
Cutting Tips for Beautiful Bouquets
When to Cut
A zinnia is ready to harvest when you shake the stem about 12 inches below the flower and the flower stays stiff. If it's not mature yet, the flower will jiggle noticeably.
How to Cut
Cut deeply down the stem—at least 20 inches—to encourage taller, stronger new growth. The longer you leave a mature flower on the stem, the more petal layers will form, creating big, fluffy blooms. The flowers pictured were left to mature on the stem for 14 days.
Vase Life
Cut zinnias will last 6-9 days in a vase if you:
Change the water every other day
Use flower food
Snip an inch off the stem every four days
