How to Root Petunias in Water in 7 Simple Steps
Rooting petunias in water is a simple way to create more of the vigorous flowering annuals. Gardening expert Katherine Rowe explores how to root the summertime favorites in water so we’ll soon have new transplants to infill the display.
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Petunias are among the most popular flowering annuals for their easy color with showy blooms and a long bloom season. Their mounding and cascading stems quickly fill a container, spill over a hanging basket, or sprawl along a low wall with color-lined stems. The sweet nectar and light fragrance draw pollinators like hummingbirds and butterflies while the blooms last until frost.
The summer garden can always use more petunias, and one way to make more is to propagate them from vegetative cuttings. Petunias’ long stems root easily in water, letting us create a new crop to fill in garden gaps, tuck into pots for a late-season bloom, or even to grow out over the winter for transplanting in spring. It’s a quick, easy, and economical way to produce more plants. And, growing a successional round brings fresh blooms when the early starts take a mid-summer break.
Rooting petunias in water is a resourceful and straightforward process. It’s rewarding, too, to see the new plants develop before our eyes. While propagating cuttings in a soil mixture is the primary way to propagate stem cuttings, rooting in water is a space-saving, no-mess way to enjoy the display while plants root. And, they root just as quickly or more so in water than in potting media.
Shock Wave Purple Tie Dye Petunia
Shock Wave Purple Tie Dye Petunia Seeds
Plant Selection
Any petunia with fresh, healthy, pliable stems is a candidate for cuttings (unless it is protected under a plant patent, like SupertuniaⓇ, which prohibits propagation). From mounding to cascading, the soft stems are viable for rooting.
Petunias fall into divisions based on their growth habit and flower structure. Trailing petunias are among the easiest to propagate with their lengthy stems and growth production.
- Grandiflora – Large single or double flowers, with ruffles or fringes and long, sprawling stems.
- Multiflora – Blooms are smaller than grandiflora, but more numerous, and hold up better in rain. These have a more compact habit.
- Milliflora – Miniatures that produce loads of one to one and a half-inch flowers on compact, self-cleaning stems (no deadheading).
- Spreading/Trailing – Vigorous and low-growing groundcover types with good heat and drought resistance; low maintenance and quickly fill hanging baskets and pots.
Select the Container
A small glass jar, vase, or other clear glass container is the ideal vessel for rooting petunias in water. Glass allows plenty of even light to infiltrate for photosynthesis and root development. It lets us keep an eye on water level and clarity and all those developing roots, too.
Plan to house multiple cuttings in the same container, or separate them by variety if taking cuttings from multiple selections. If so, a label helps keep track of them as they grow.
Sanitize Materials
To sterilize the container, give it a wash in hot, soapy water. The cleanse prevents bacteria from building up, and creates a sanitary environment to preserve the health of the cutting and new roots. Soaking reused vessels in one part bleach to nine parts water eliminates any carry-over problems.
Take Cuttings
Petunias’ long stems make them ideal for starting in water. Take cuttings early in the summer, for an infill round of plantings, or closer to fall for overwintering. It can take five to six weeks for a successful cutting to be ready for transplanting.
Select fresh growth that hasn’t flowered yet, and clip a four to six-inch length. If the only options are flowering stems, remove any flowers and buds before sticking them in the jar. Take off all leaves from the lower portion of the cutting, leaving one or two sets intact on the upper end.
During the growing season, petunias benefit from pruning to rejuvenate growth and promote continual flowering. A regular trimming session is prime time to collect cuttings. Cut the green stems just above a leaf node (where leaves meet the stem) so the remaining stem will generate new growth. Cut the stem by about 20% or as much as 50% for pruning and shaping.
Stick the new cutting into a jar filled with shallow water. Leaf nodes should be under water, but the upper stems and leaves should be above the surface. Too much water can damage the stem’s viability.
Provide the Best Placement
With the stems in their fresh containers, place them in a bright spot. The flowering annuals grow best near a light-filled window, but there is also some evidence that dark exposure for a few days before light exposure can enhance rooting. An east-facing window gives good morning sun exposure, while a south-facing window provides the most. Filtered light in the afternoon (like through a curtain) protects tender growth. Ample light and a sunny exposure for several hours a day promote stem and root development.
Tending While Rooting
Once situated, check the water level regularly to account for uptake and evaporation. Empty and refresh it every few days to keep it from becoming cloudy, murky, and stagnant. Fresh, oxygenated water helps generate healthy roots.
Rotate the vessel when changing the water for even light exposure as the stems grow. It may take two or three weeks for the petunias to root in water and to develop a good root structure.
After Rooting
New plants are ready for transplanting when their roots grow beyond one to two inches. You can opt to transplant them into their garden location, gradually acclimating them, or place the rooted cuttings in moistened potting soil in a small pot. Put the pot in a spot with the same bright light conditions to continue growing.
Hardening Off and Transplanting
After a few weeks in the pot, the young plants are ready to move to the garden. Tender seedlings benefit from gradual acclimation from the indoor growing situations to garden conditions. Before transplanting, place them in a protected outdoor area for a few days to a week. Slowly move them to conditions mirroring their new garden location. Protect them from strong winds, cold nights, and afternoon sun in the process.
If you’ve overwintered the propagated petunias, transplant the seedlings after the last frost. Follow spacing guidelines according to the variety to allow for growth and airflow between plants, usually 8-12 inches apart.
Ideal growing temperatures are around 55 to 80°F (13-27°C). While the annuals flourish in mild summer temperatures, high temperatures cause stress and result in fewer flowers. Hot spells slow growth and production.
Petunias are frost-sensitive, and late spring frosts, chilly nights, and early fall cold snaps inhibit flowering. Growth slows when nighttime temperatures fall below 40°F (4°C). Overwinter potted petunias until the next growing season.
Care After Planting
Petunias are easy-going annuals, but they’re not maintenance-free. To promote the best growth and flowering, provide consistent moisture and give a boost in nutrition at planting and during the growing season.
Water and Fertilizer
Young seedlings and transplants have small root systems, and consistent soil moisture throughout the growing season is best. Site them in well-draining soils to prevent problems at the root level.
Once established, the adaptable annuals tolerate short periods of drought and can dry out between waterings. If the soil is dry to the depth of an inch (one knuckle deep), it’s time to water. Containers and hanging baskets dry out quickly in the summer heat, and depending on your climate, they may need water daily.
As petunias do all their growing and prolific flowering in a single season, they’re heavy feeders. Apply an organic balanced fertilizer like 8-8-8 or 10-10-10 at planting. A slow-release granular sustains plants for about two months and distributes nutrients over time.
A liquid feed later in the season gives a boost. Petunias benefit from applications starting in June (every few weeks) and increasing in July to every two weeks. Use a formula specific to flowering plants to boost blooms with higher phosphorus (P). Phosphorus is more beneficial than high nitrogen (N) in the flowering phase.
Deadheading and Trimming
Petunias may become spindly as the season wears on, and their long stems grow leggy. To give them a refresh, opt for a light prune in midsummer. Repeat the trim in late summer or early fall as needed. Clipping the stems promotes new growth and flowering.
Many petunias, including smaller-flowered and newer cultivars, are self-cleaning and don’t require deadheading to promote blooming. Some selections, including old-fashioned grandiflora varieties with large or double blooms, benefit from removing spent blooms. Deadheading the blossoms and sepals prevents the annuals from going to seed, channeling energy into flower production instead.
In addition to growing petunias from vegetative cuttings, they also grow from seed. Choose your favorites for a floriferous selection.
