With cheery, daisy-like blooms in a myriad of dazzling colors, it's no surprise that zinnia's top many gardeners must-grow list. With perfect rounds of petals arranged either as a simple, single layer or multiples, these easy-going annuals offer something for every taste.
Relatively simple to raise from seed; either under cover mid-spring or direct sown when frosts have passed, there's no doubt that knowing how to grow zinnias can transform any summer yard.
Whether filling pots, boosting borders or brightening pathway edges, these pollinator and florist favorites seldom fail to disappoint, but they do appreciate the occasional boost to keep them flowering until the first frosts. My favorites to sow this year are the 'northern lights' seed mix from Botanical Interests. Here we delve into what care zinnias need this month.
Promptly Remove Fading Flowers
Just a little care can keep zinnias performing throughout July, and beyond.
'This is the one task that makes the biggest difference to zinnias in July,' explains Stephan Winterfeldt, Horticulturalist at Park Seed. 'Cut spent flowers right down to the next set of leaves or a side shoot, not just snipping the flower head off.
'That stimulates branching and more flower stems. Do it every few days and a zinnia patch will keep flowering right through to frost. Skip it for a couple of weeks and the plant really slows down.'
Remove spent blooms with a clean, sharp pair of slim-nosed snips, such as these Corona shears from Lowes.
Keep A Check On Tall Stems
With 18 species and hundreds of varieties, zinnias come in all shapes and sizes but those with long stems need close supervision.
‘Stake taller varieties to keep them upright through strong winds,' suggests master gardener Pamela Reardon. Essential to avoid broken stems and damaged flower buds, consider supporting bushy plants with the best natural supports, metal half hoops from Lowe's or a grow-through plant grid, such this one, also from Lowe's.
During July, straggly stems can appear untidy and will benefit from pruning back. 'If plants have gone leggy and bare at the base by midsummer, cut the whole plant back by about a third,' says Stefan. 'It looks severe but zinnias generally recover well in warm weather. With water and a light feed afterward, you'll usually see a bushier plant with more flowering stems soon after.'
Benary's 'giant blend' zinnia seeds from Botanical Interests are ideal if you're looking to grow tall varieties.
Feed Container Grown Zinnias Fortnightly
By midsummer, zinnias are flowering non stop and container grown plants have depleted the nutrients in the compost. To keep them performing we need to feed as well as water.
'In containers, or where soils are especially lean, I like giving zinnias a balanced liquid fertilizer every couple of weeks during active flowering,' says master gardener Tabar Gifford. Try SuperThrive Liquid Concentrate from Amazon.
Plant expert Katie Sunderlage also cautions to water and feed wisely. 'Avoid overhead watering, instead soaking thoroughly at the base of the plant, especially on cactus or pompom varieties. The double blooms can trap moisture, causing rot or mold.'
Walmart's long spout watering can help to direct liquid.
Take Action Against Powdery Mildew
July's warm and humid conditions are perfect for powdery mildew. 'Zinnias are highly prone to powdery mildew, so make sure plants are well-spaced for good airflow,' says Lindsay Del Carlo, Trial Garden Manager at Renee’s Garden.
'It's wise to anticipate powdery mildew and give susceptible plants a pre-emptive spray of an organic fungicide – copper, sulfur, neem oil, or a baking soda solution – before you even see it. If white powdery spots appear on the leaves, treat them right away to keep it from spreading.'
Your watering method can also help combat this fungal disease. 'Water deeply once a week, providing about 1 inch of water, applied at the base using soaker hoses or drip irrigation,' continues Lindsay.
'This avoids overhead watering, which wets the foliage and invites fungal disease. Let the top 1–2 inches of soil dry out between waterings.'
Find soaker hoses of different lengths at Walmart , and head to Amazon for neem oil.
Keep Picking... And Enjoy Blooms Until Fall
Nothing celebrates July more than a vase full of zinnias and cutting stems actually helps the plant too. Tabar explains, 'When a zinnia finishes blooming and you leave the spent flower in place, the plant shifts its energy toward producing seed. Cut that flower the plant responds by branching and sending up multiple new flowering stems.'
Handle the hollow stems carefully to avoid crushing them and cut at a 45 degree angle, just above a leaf node. This deters disease, aids branching growth and enables the cut stem take up water.
These Darlac deadheading snips from Amazon are pocket friendly and easy to use. Keep the blades clean with this specialist tool cleaner, also from Amazon.
What to Shop
Hopefully you now feel confident nurturing zinnias through the summer, however its also worth knowing how to grow zinnias in pots plus the 7 plants never to grow next to zinnias.
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