Delphiniums are one of the standout flowers of midsummer, bringing vertical interest and classic cottage garden charm to borders. But by July, many gardeners begin to notice fading blooms, drooping stems, or foliage struggling under the pressure of soaring temperatures.
Whether you’re growing tall Pacific Giant cultivars, compact varieties for smaller yards, or other popular delphinium types, July is a crucial month for maintaining their health and appearance. Knowing how to care for delphiniums during periods of intense heat can make the difference between plants that fade quickly and those that continue performing well into late summer.
This month is all about helping plants recover from their first spectacular display while protecting them from summer stress. With much of the US experiencing hotter-than-average temperatures and prolonged dry spells, a few timely maintenance jobs can encourage a second flush of flowers and keep plants healthy for the rest of the season.
Here are the five jobs gardening experts recommend tackling now.
1. Deadhead Spent Flower Spikes to Encourage a Second Flush
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The biggest July job is removing faded flower spikes as soon as they’ve finished blooming. If you’re looking for plants to deadhead in July, delphiniums should be high on your list, as timely pruning can encourage a welcome second display later in the season.
‘Deadheading is the most important thing you can do for delphiniums in July,’ says Rachel Bull, Head of Gardens at Homes & Gardens. ‘Many varieties will reward you with a second, lighter flush of flowers later in the summer if you cut back the spent spikes before the plant starts putting energy into producing seed.’
To cut back delphiniums correctly, wait until most of the florets on a flower spike have faded, then cut the stem back to a healthy side shoot or down to the base if no new growth is visible. A sharp pair of Fiskars Bypass Pruning Shears, available from Amazon and The Home Depot, will make clean cuts that are less likely to damage stems. If your delphiniums have reached their full height, it’s also worth checking their supports while you’re pruning. Grow-Through Plant Supports, sold at Amazon, help keep tall flower spikes upright through summer downpours and strong winds.
‘Don’t be tempted to leave the seedheads for too long if repeat blooms are your goal,’ Rachel adds. ‘The sooner you deadhead, the better the chances of encouraging fresh flowering.’
2. Water Deeply During Heatwaves
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While delphiniums appreciate consistently moist soil, they’re not particularly tolerant of prolonged drought. During periods of extreme heat, they can quickly become stressed, causing blooms to fade early and foliage to wilt, so knowing how to water in hot weather is key to keeping plants healthy through July.
‘If you’re experiencing a heatwave, deep watering is far more effective than little and often,’ says Rachel Bull. ‘Aim to soak the soil once or twice a week, depending on rainfall and your soil type, so moisture reaches the deeper roots.’
Water early in the morning to reduce evaporation and help plants cope with rising daytime temperatures. A Gilmour Heavy Duty Adjustable Metal Hose Nozzle, available from Amazon and Walmart, makes it easy to switch between a gentle shower for soaking borders and a stronger stream for other watering jobs around the yard.
Adding a two- to three-inch layer of compost or other organic mulch around the base will also help conserve soil moisture, regulate root temperatures, and reduce the need for frequent watering throughout the hottest weeks of summer.
3. Check Supports Before Summer Storms
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July often brings intense thunderstorms across much of the US, and tall delphinium flower spikes are particularly vulnerable to strong winds and heavy rain. Even if you staked plants earlier in the season, now is the time to make sure supports are still doing their job.
Soft twine, bamboo canes, or grow-through plant supports all work well, provided stems have enough room to move naturally without rubbing. A pack of Ecostakes Bamboo Garden Stakes, available from The Home Depot, is an inexpensive and versatile option for supporting tall delphiniums, while soft garden ties can be used to gently secure stems without damaging them.
4. Feed After Flowering to Support Fresh Growth
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Once you’ve deadheaded the first flush, giving plants a light feed can help fuel new shoots and encourage repeat flowering. A balanced fertilizer or one that’s slightly higher in potassium is ideal after flowering, as it helps plants recover without encouraging lots of soft, leafy growth that can struggle during hot weather.
Miracle-Gro Water Soluble Bloom Booster Flower Food, available from Amazon, is a popular option for supporting flowering plants and can help provide the nutrients delphiniums need as they recover from their first bloom cycle.
Always water well after feeding, particularly if temperatures are high, to help nutrients reach the root zone without scorching stressed roots.
5. Keep an Eye Out for Powdery Mildew
Hot days followed by humid nights create ideal conditions for powdery mildew, one of the most common problems affecting delphiniums in midsummer. Good airflow is one of your best defenses, so remove any badly affected leaves, avoid overhead watering where possible, and make sure neighboring plants aren’t becoming overcrowded.
It’s also worth checking for slugs and snails around fresh new shoots after deadheading. Although they’re more active in spring, they can still damage tender regrowth later in the season. For an easy, targeted solution, Safer Brand Insect Killing Soap, available from Amazon, can help tackle soft-bodied summer garden pests while being gentle enough for use around ornamental plants.
The key to keeping delphiniums thriving through summer is avoiding a few simple mistakes. Don’t allow plants to dry out completely during hot spells, as drought stress can shorten flowering and reduce the chance of a second flush.
Stay on top of deadheading, too – removing spent spikes promptly encourages fresh growth rather than seed production. And resist cutting back healthy foliage too early, as the remaining leaves continue to feed the plant and store energy for next year’s blooms.