Gadenin日本語Get the appWater the soil, never the foliage
Zinnia leaves are broad, slightly rough and slow to dry, and every time you spray them with a hose you hand powdery mildew and leaf spot a few free hours of wet surface. Put the water on the ground at the base of the plant instead. A can with the rose taken off, a soaker hose laid along the row, or a wand held below the leaves all do the job. This single change delays mildew by two to four weeks in most gardens.
Water deeply and infrequently. A thorough soak that wets the top eight inches (20 cm) twice a week beats a daily sprinkle, because shallow watering keeps the roots near the surface and leaves the plant helpless in a hot spell. Established zinnias are genuinely drought tolerant once the taproot is down, and a plant that has been made to search for water stands up better in wind.
Water in the morning if you have a choice. Foliage that does get splashed then dries within the hour, whereas an evening watering leaves the base of the plant damp all night, which is when mildew spores germinate and slugs feed.
| Condition | Watering | Signs you have it wrong |
|---|---|---|
| First fortnight after emergence | Light water every 1 to 2 days | Seedlings wilting by midday, or damping off at soil level |
| Established plants, ordinary weather | A deep soak twice a week | Leaves flagging by mid afternoon and recovering at dusk |
| Hot dry spell above 85F (29C) | A deep soak every 2 to 3 days | Lower leaves yellowing and dropping, flowers small |
| Wet humid weather | Stop entirely and let it dry | White dusting on lower leaves, brown blotches spreading upwards |
| Plants in containers | Check daily, water when the top inch is dry | Wilting every afternoon means the pot is too small |
If you have overhead irrigation you cannot change, run it at first light rather than in the evening. The leaves are then dry within an hour or two instead of staying wet through the night.
Feed lightly, or you get leaves instead of flowers
Zinnias flower best on moderate soil. Heavy nitrogen produces a tall, soft, dark green plant that flops in the first storm, mildews early because the growth is lush and crowded, and carries far fewer flowers than a leaner plant beside it. If your bed has just had a load of manure, sow something else in it and put the zinnias where the ground is plainer.
A single application of a balanced general fertilizer worked in before sowing is enough for most soils. Once the plants are flowering, a liquid feed higher in potassium than nitrogen every three or four weeks keeps flower size up without pushing soft growth. Skip it entirely if the plants already look dark and leafy.
Container plants are the exception, because watering flushes nutrients out of a pot fast. Feed those fortnightly at half strength from the point the first buds show, and be prepared to feed weekly by late summer when the roots have filled the pot.
Support the tall types before they need it
Tall zinnias carry heavy flowers on hollow stems and go over in one squall of summer rain. Once a stem has bent it never straightens, and a leaning plant sprawls onto its neighbors, which shuts down the air movement you spaced them out to get. Put support in when the plants are a foot (30 cm) high, long before it looks necessary.
The best support for a block of cutting zinnias is horizontal netting, a single layer of six inch (15 cm) mesh stretched over the bed on stakes and raised as the plants grow. The stems come up through it and hold each other. For a handful of plants in a border, a short cane behind each one with a loose tie at eighteen inches (45 cm) is enough.
Pinching the plants early, which you do anyway for cut stems, also makes them shorter and sturdier, so support and pinching work together. A pinched zinnia branches from low down and carries its weight better than a single tall unpinched stem.
- Stake at knee height Drive stakes at the corners and every three feet (90 cm) along a block when the plants are around 12 in (30 cm) tall. Doing it later means pushing stakes through roots you have spent two months growing.
- Lay netting flat and raise it Stretch one layer of wide mesh netting at 12 in (30 cm) above the soil and lift it up the stakes as the plants grow through, keeping it around two thirds of plant height.
- Tie loosely in a figure of eight For single canes, cross the tie between cane and stem so the stem is not pressed against the wood. Zinnia stems are hollow and crush easily under a tight tie.
Keep the base clean and keep cutting
Strip the lowest leaves off each plant once it reaches around eighteen inches (45 cm), taking off the bottom four to six inches (10 to 15 cm) of foliage. Those leaves are the first to catch mildew and leaf spot, they get splashed with soil at every watering, and the plant loses nothing by giving them up. A clear stem base also lets air move under the row.
Take off any leaf that has gone yellow, blotched or dusted white and carry it out of the bed rather than dropping it. Leaving diseased leaves on the ground under the plant keeps the spores exactly where the next splash will lift them back up.
Beyond that, the main job is simply to keep cutting or deadheading. A zinnia left to set seed slows down and then stops, whereas one that is picked over every few days keeps producing until frost. That is covered properly under flowering, but treat it as part of routine care rather than an occasional treat.
Record the date you first strip the lower leaves and the date mildew appears. In most gardens the gap is remarkably consistent year to year, which lets you plan a preventive strip a week earlier next season.