Before we attempt to rid our zinnias of powdery mildew disease, let’s first hear from Debbie Flower, who has plenty of zinnia growing tips for us in today’s podcast. Here’s the quick summary of our chat, which included how to cut outdoor flowers for indoor use. A complete transcript can be found at the bottom of today’s newletter.
* Plant zinnias in full sun. They’re heat and drought tolerant, and bloom most prolifically when days are under 12 hours (expect peak blooms in fall). Planting zinnias where they get full sun, with proper spacing (18”-24” apart) is also great cultural controls for thwarting a powdery mildew breakout.
* Succession-plant every two weeks through early summer for a continuous supply of cut flowers. This is also a good powdery mildew control strategy. Trash (don’t compost) heavily infected zinnia plants. Plant new seeds where you want them to grow!
* Wait until soil is at least 70°F to sow seeds. Germination requires warm soil.
* Cover seeds lightly with vermiculite. It marks where seeds are planted and retains moisture during germination.
* Don’t plant two seeds per spot if using fresh seed. One is enough; double-sowing is only needed to compensate for old/marginal seed.
* Avoid overhead irrigation. It spots flowers and splashes soil onto foliage, promoting disease. Use drip or soaker hoses instead. Another powdery mildew prevention strategy.
* Space plants so they never touch neighboring plants. Good airflow prevents powdery mildew and Alternaria leaf blight.
* Transplant zinnias early. Don’t let nursery starts become root-bound; roots disturbed at that stage cause double-flowered varieties to revert to singles. And don’t buy zinnia plants with powdery white substances on the leaves!
* Pinch young plants (at 4 nodes, remove 1–2) for a bushy, branched plant with more but shorter stems. Skip pinching if you want tall stems for large bouquets.
* Cut flowers in the morning. Plants move carbohydrates (food) into flowers overnight, so blooms are fullest and will last longest when cut early.
* Cut stems at a node, leaving at least one axil bud on the remaining stem. That bud becomes the next flower stalk. More axil buds left = more future stems; fewer = longer current stem.
* Strip leaves that will sit below the waterline and remove side branches from the cut stem before putting in a vase.
* Use floral preservative in vase water, or try hot water. Zinnias last 5–7 days as cut flowers. They will last longer if you do refresher cuts from the bottom of the stem every other day, and add fresh water.
* Use California buckwheat (Eriogonum fasciculatum) as filler in zinnia arrangements. Outdoors, California buckwheat attracts pollinators and has attractive clustered flower heads.
* Support tall varieties in windy or rainy locations with a small tomato/pepper cage. The small cages sold at big-box stores that are useless for tomatoes are well-sized for large zinnias.
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