Dahlia Care in July: What to Do Right Now

Water deep, and more often than you think

Heat changes the watering math. A dahlia in full July growth is moving a lot of water, and short, shallow sprinklings do not reach the tubers where it matters. Extension guidance is to water deeply and less often, soaking the root zone so the moisture goes down rather than sitting on the surface, and to do it more frequently as the temperature climbs. Inconsistent water is the usual reason for stalled or undersized blooms in midsummer, so the goal is steady, deep moisture, not a daily splash.

A few inches of mulch around, but not touching, the stems buys you margin: it holds moisture, keeps the root zone cooler, and slows the surface from baking hard between waterings.

Switch the feed from leaves to flowers

This is the July move most gardeners miss. Early on, some nitrogen builds the plant. Once it is budding, high nitrogen works against you, pushing soft leafy growth at the expense of flowers. The grower's answer is to ease off nitrogen now and favor a lower-nitrogen feed with more phosphorus and potassium, the sort sold for tomatoes or blooms, which supports flowering and stem strength rather than more foliage. Feed on the label's schedule through the blooming season and then stop well before you plan to lift, since late feeding pushes soft growth into fall.

If your plants are all leaf and few buds, over-rich soil or a high-nitrogen feed is the first thing to suspect.

Get ahead of the summer storms with staking

A dahlia carries its heaviest load exactly when summer storms arrive, and a single downpour can flatten an unstaked plant and snap the hollow stems for good. If you have not already, stake now, before the plant needs it, and tie the main stems loosely to a stout support as they gain height. The big decorative and so-called dinnerplate types are the most vulnerable, since a large bloom acts like a sail in wind. Our guide on how to pinch and stake dahlias covers the method; July is the month to make sure it is actually done.

Disbud for bigger, cleaner blooms

Look at the tip of a flowering stem and you will usually see three buds: a central one flanked by two smaller side buds. Removing the two side buds while they are small sends the plant's energy into the single remaining flower, giving you a larger, longer-stemmed bloom on a cleaner stem. This is standard practice for exhibition and for cutting, and it is worth doing on your best plants even if you never enter a show. If you would rather have more, smaller flowers for the border, you can skip it. It is a choice, not a rule.

Keep deadheading, and start cutting

Dahlias only keep blooming if you keep taking flowers off them, spent or fresh. Deadhead faded blooms so the plant makes new buds instead of seed; the one trick is telling a spent flower from an unopened bud, which our guide to deadheading dahlias walks through. July is also when the vase season really begins: cut in the cool of the morning, take stems longer than feels comfortable, and the plant answers with more. Cutting is deadheading that happens to end up in a jug.

Watch for the July pests

Warm weather brings the chewers. Slugs and earwigs work at night and leave ragged holes in petals and leaves, so check after dark if damage appears. In hot, dry spells, watch the undersides of leaves for the fine stippling and webbing of spider mites, which thrive in heat and multiply fast. Humid stretches can bring powdery mildew as a dusty film on the foliage; improving airflow between plants helps. Catching any of these early, while it is a few plants rather than the whole bed, is most of the battle.