In the Garden:
Coastal and Tropical South
Strawberry begonias wait to be divided as rooted begonias and sago palms get growing.
Good candidates for propagating even in the heat of August include many perennials that you'll want to plant or share over the next few months.
The bench outside my greenhouse is crammed full of baby plants and pots waiting to be divided or thinned. While it's too hot to till, propagating a slew of plants under the shade of a big oak tree is pleasant. Candidates range from overgrown perennials to annuals you'd like to restart to overcrowded pots of foliage plants. The same essential principles apply to a wide variety of plants.
So put a shady spot to work by setting up a rooting area. A simple wire shelf elevated by a couple of bricks provides the necessities: drainage and good air circulation around the pots.
Begin by making a very well-drained potting mix. Start with a bag of good potting mix and note whether it also includes fertilizer or water-holding polymers. Mix equal parts of your soil and ground bark, not shredded nor in chunks. For every 15 gallons or so of soil mix, add some sharp sand or grit (up to a quart if rooting succulents), one cup of dolomite lime and one cup of your favorite granular fertilizer if none is included in the original bag of mix. Mix the ingredients well and store covered until used.
Pots and Proper Care
Propagating is a great way to recycle small pots, but reserve the largest for repotting container plants that grow out of bounds. Small pots (3" to 5") can be useful for many plants, quart size for most perennials or 1 gallon for really large plants like rice paper plants. Clumping tropicals like rice paper produce many offsets in summer that can be lifted with little disturbance to the main plant. Pot them up right away and by October they'll have plenty of new roots and probably a new leaf or two. Use the smallest pots for plants that need to be dry during rooting such as cacti and bromeliad pups. For the average 4"-6" cutting such as begonia, use a 4" pot.
While it might seem thrifty to stick lots of cuttings in a larger pot or tray, there is a much greater potential for transplant shock. When the roots of two plants grow together in the rooting tray, separating them can tear precious tissue. It will be easier and less traumatic to squeeze the pot and remove the roots intact. During the weeks it takes to root, keep the plants watered, adding fertilizer to the water weekly, and keep them in the shade. Gently tug at the stems after two weeks; if it resists, it is rooting, but do not rush the process. The appearance of a new leaf or sprout is a very good sign.
Cuttings and Divisions
Take cuttings in summer from herbaceous plants, those that grow with green stems each year. The group includes green cane plants such as dumb cane and dieffenbachia. Indeed, most "tropical foliage plants" root well from summer's abundant growth whether we grow them in pots or a garden bed. If such a plant is not doing well, like a lanky schefflera too long in a dark corner, cut it back and root the tops. Along the southern coasts, root cuttings of coleus and other annuals now. They'll brighten the porch all fall in pots and can give you a leg up on next spring's planting.
Strawberry begonia (aka strawberry geranium) and others that send out runners can be propagated 2 ways. Set small pots around the mother plant and secure the babies in them with a hairpin-shaped piece of wire. Do not cut them apart for about a month. Or you can separate crowded plants, keeping any "babies" attached. Pot up the mother plant, then lay the stem with the new plant alongside it in the pot for a doubly delightful new pot.
You can also divide any perennials that have finished blooming for the year, such as daylilies, iris and stokesia. Lift them out of the bed, separate by hand or with a sharp knife, then trim back the tops by about half before potting. Roots will form by fall when transplanting weather is usually favorable.
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