Start seeds in individual cells and then transplant them into a small pot once they have developed two pairs of real leaves. If you want to plant Pentas from seed, you can do so indoors two months before the first frost or outdoors when the weather is consistently warm. Make sure to provide new plantings with plenty of water. In a few weeks roots will begin to grow and the plant will be ready to be transplanted. Place the new plant in an area that is protected from sun and wind, keeping the soil moist. Take a cutting from the parent plant early in the morning, stripping away leaves that are near the cut end, and any blossoms, and then dipping the cut end into rooting hormone before placing it in the prepared pot. To do so simply prepare small pots with a moistened mix of peat moss and perlite, making a hole in the planting medium with a pencil or chopstick. Pentas can be planted from seeds but they are remarkably easy to propagate from cuttings. The plant benefits from being fertilized in the spring with a slow release granular fertilizer and then followed every six weeks with a water soluble version that it can absorb quickly. After it is acclimated to its new location it will require little attention, only needing water when rainfall is sparse. When you first plant your Pentas keep its soil moist to allow the root system to become established. Pentas do very well as container plants and if you live in a cold weather area bring the Pentas inside and place it in a sunny spot over the winter months.
Pentas do not tolerate the cold, so if frost is expected, they can be protected by covering them with a sheet or placing warming lights around them. A couple inches of mulch at their base helps them hold onto their water and keeps weeds away. Pentas need enough room to reach their mature size of 15 inches wide and three to four feet high. They also do well in a shadier area but will produce fewer blooms and will grow leggy as they reach for the sun. Whether your garden is in a warm weather area where the Pentas thrive as a perennial, or a colder zone, where it grows as an annual, choose a sunny spot with well drained, mildly acidic soil.
It is a good idea to replace old, woody specimens with a freshly propagated plant every few years, as they do lose vitality eventually.By Jo Cosgrove | Ecological Gardener, Horticulturist, and Educator – last update on December 2, 2021 From this, I learnt is that it seems to help to put the cutting in water for a week or so before it is potted up. They are useful as cut flowers, and strike reasonably readily from cuttings taken in spring or autumn: one of my prettiest pink cultivars (pictured above) came to me as a part of a birthday posy many years ago. I do trim them very lightly from time to time during their flowering season to promote extra blooms. In areas of Sydney with very cold winters, they may not survive: it is a good idea to take cuttings in autumn and plant these out in spring. The plants do look a bit sad in winter: denizens of tropical Africa, Madagascar and the Arabian Peninsula, they don't enjoy the colder months but they will generally survive an average Sydney winter, as long as they are not pruned until the warmer weather returns in September. Pentas needs just ordinary, well-drained soil and occasional watering - it seems to stand up to the summer onslaught of heat very well.