Propagating cuttings through a Cape Town winter

Somewhere around the end of May, cuttings that rooted in a fortnight start taking six weeks. Nothing has gone wrong. It is just winter, and roots are temperature and light before they are anything else.

The Cape winter is a particular kind of difficult. It is not cold enough to kill a houseplant cutting, but it is cold enough and dark enough and damp enough to make one sit in a tube doing nothing for two months. Understanding why makes the waiting less annoying.

What the numbers actually say

Cape Town in July averages a minimum of about 7°C and a maximum of about 19°C. That maximum is only reached outside, in the sun, in the middle of the day. Most Cape homes have no central heating and not much insulation, so an interior room sits somewhere in the mid-teens for most of the day and drops overnight.

Commercial propagators aim for a rooting medium around 23–25°C. That is not a nice-to-have. Root initiation is a metabolic process and it slows down as the temperature drops. A cutting in a jar at 15°C is not refusing to root. It is rooting at about a quarter of the speed.

Then there is light. Cape Town gets roughly ten hours of daylight in July against about fourteen and a half in December, and six hours of that is behind cloud on the average winter day. A cutting has no roots, so it cannot take up much water, and it has to fund root growth out of stored sugars and whatever photosynthesis it can manage on a dim windowsill. Less light means less fuel.

And it is wet. July brings around 85 mm of rain across roughly ten days. Cape houses in winter are damp houses. Still, humid air with no movement is exactly what stem rot and grey mould want.

So what actually roots in June, July and August

Some things do keep going, slowly. Broadly, the soft-stemmed, fast-growing, tropical foliage plants are the ones worth trying.

• Pothos and its relatives. Reliable in winter, just slow. Expect five to eight weeks rather than two to three.
• Tradescantia. Roots at almost any temperature, which is part of why it is a listed invasive in this country. More on that another time.
• Philodendron, including the common heart-leaf and the 'Hope' types. Slow but willing.
• Plectranthus, the indigenous spurflowers. Soft stems, shade-adapted, and they root in water without complaint. Not their preferred season, but they cope.
• Spider plant babies. These already have root nubs on them before you cut, so you are not really propagating, you are just finishing a job the plant started.
• Delicious monster nodes, if you can find them a warm spot. Two to four weeks in summer, comfortably double that now.

What is not worth starting in July:

• Anything succulent. Spekboom, crassulas, string of pearls. Cold plus wet plus dormant is a rot recipe. Wait for October.
• ZZ plant. It takes up to nine months from a leaf in good conditions. In a Cape winter you are effectively starting a project you will forget about.
• Snake plant leaf sections. Same problem, and the variegated ones lose their stripes from leaf cuttings anyway.
• Fiddle-leaf fig and rubber plant. Both want warmth to callus and root. They sulk.

Where to put a propagation station in a Cape house

This is the part people get wrong, and it is mostly about aspect.

In the southern hemisphere the sun sits in the northern half of the sky. A north-facing window gets the winter sun. A south-facing window in Cape Town gets bright shade and, from June, a cold draught off the Atlantic side of things. If you have one good north-facing sill, that is where the cuttings go from June to August. In summer you will want to move them off it again, because a north window in January will cook a bare stem.

Some more specific placement notes:

• Not touching the glass. Single glazing at 2am is a cold plate, and a glass tube pressed against it will drop several degrees below room temperature. A hand's width back from the pane is enough.
• Off the sill overnight if the sill is stone or tiled. Those go properly cold. A wall mount a little above the sill, or a bar hung across the window, keeps the tubes in the light but out of the cold pool at the bottom.
• Near a kitchen, not in a bathroom. This is the opposite of the usual advice, but Cape bathrooms in winter are the dampest rooms in the house and often the coldest. A kitchen counter or the top of a fridge is warmer and drier. The fridge top is genuinely one of the better spots — steady gentle warmth from the compressor, and nobody uses that space anyway.
• Away from a heater blowing directly on the glass. Warm is good. Hot dry air on a leafless cutting is not.
• Some air movement. Crack a window for ten minutes a day. It costs nothing and it is the single best thing you can do about mould.

Our hanging bars and wall mounts exist partly because of this. In a Cape flat the warm, bright spot is very often a wall next to a window rather than the sill itself, and there is rarely a shelf going spare.

Water, in winter

Change it when it goes murky, or top it up as it drops. That is the whole rule and it does not change with the season. What does change is the pace — algae grows more slowly in the cold and in lower light, so you will find yourself topping up more often than replacing.

One small thing: Cape tap water in July comes out of the pipe genuinely cold. Filling a tube straight from the tap drops the cutting's temperature by several degrees for an hour or two. Fill a jug and leave it on the counter overnight, then top up from that. It is a marginal gain, but marginal gains are all winter offers.

Do not add fertiliser to the water. A cutting with no roots cannot use it, and it feeds the algae.

Realistic timelines

Take whatever you would expect in February and roughly double it. As a rough guide for an unheated Cape Town room in July:

• Tradescantia: one to two weeks
• Pothos: five to eight weeks
• Philodendron: six to ten weeks
• Plectranthus: three to six weeks
• Monstera node: six to twelve weeks, and then another few months before a leaf
• Anything succulent: no

Two more honest notes. First, a cutting that has done nothing for six weeks is often still perfectly alive — a firm stem and a green leaf means it is waiting, not dead. Slimy stem means it has gone, and no amount of patience fixes that. Second, roots that form in cold water in low light tend to be thin and brittle. Pot them up gently, and expect a week or two of sulking while the plant swaps water roots for soil roots.

The useful thing to do in July

Take the cuttings you can take now, put them somewhere sensible, and then leave them alone. Then make a list for September. The first warm week after the rain breaks is when everything moves at once, and it is much more satisfying to have the tubes cleaned and the secateurs sharp before that than to be scrambling.

Roots take their time. In winter they take a bit more of it.