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Great Gardening: As autumn draws near, it’s time to decide which plants are coming inside

The air was suddenly chilly one morning last week. I’d returned home from a trip the night before and was eager to see my plants on the deck. I put on my cozy pink robe and went outside, coffee cup in hand. The plan was to relax for a few minutes among the plants and then get back to work deadlines at my desk. Relief! Most plants looked great, especially all the begonias. Just a few plants were drooping. My fault, I thought: Must stay home more and water better.

But that nip in the air spoke to me: Winter is coming. These plants will be going back inside – or at least most of them. (Which ones are too big, do poorly inside, or develop pest problems? Which should just go to the compost pile? Tough decisions.) And some plants need serious attention before they are living room-worthy. I pulled out the potting mix, put on the gloves and started: It was the first “Potting Up Day.”

Decisions

Over the years my taste has changed as well as my practical needs. In the early ’70s in a New York City apartment I displayed my houseplant collection in ceramic pots with a French blue-and-white pattern. They were beautiful, hanging in white macramé plant hangers (remember those?) in my grimy east-facing window in the West Village. I named the plants Louise, Jacques, Maurice, etc. since I didn’t know a ficus from a schefflera. I wish I’d kept those pretty pots but after several apartment moves they got away from me, and only one beefsteak begonia remains to tell the tale. Now those pots would be too heavy to use anyway.

As time passes my plants get bigger and bigger and my slightly arthritic hands and back get more fragile, so now I mostly use plastic pots. Inside the house I sink them into decorative outer pots, called “cache pots,” mostly from yard sales. They may be heavy but I can lift the plants and containers separately. Every year the pairings change – the mix-and-match game always part of the fun of decorating with plants.

That morning on the deck it was clear which plants needed help. Some were lying down sideways as they’d become top-heavy and overnight wind had knocked them down – not for the first time. Others were so pot-bound that they needed watering almost every day. Some plants do thrive with crowded roots – clivias for instance – but there is a limit. That old beefsteak begonia and its young relatives were crawling over the lips of their pots. So I pulled out the various containers I had stored, made sure they were clean and lined them up on the picnic table.

The potting-up process

One favorite plant is difficult to handle: the Crown-of-thorns, Euphorbia milii. This cultivar was brought from Florida to Lockwood’s Greenhouse long ago by the houseplant manager Donna Connelly, who propagated many from one plant with unusual yellow flowers and large leaves. I fell for it in spite of its prickly nature. But now it is 2 feet tall and tips over in the slightest breeze, so I put on the elbow-high rose gloves and went at it. I looked for a heavy pot with drainage holes but settled for a plastic one with a wide base that would help to hold it upright. Some growers would use bamboo stakes, and I even considered a tomato cage, but decided to let the plant stand up by itself or lean against a wall until the roots are stronger.

Why didn’t I just go for a much wider container? That plant needs a large, stable base – but I can’t break the basic rule for potting-up houseplants: When it’s time to transplant a crowded plant, put a small plant into the next-sized pot, typically just an inch wider than its current housing. Put larger plants into a pot just a couple of inches larger. If you give a plant lots of potting mix to grow into, it will spend years growing its roots instead of producing lovely foliage or flowers. To solve the crown-of-thorn’s tipsy problem I moved it one pot size up and cut back the plant by nearly a third. Since it’s a Euphorbia (like poinsettias and other euphorbias), the cuts produce a lot of white, dripping sap. Some people get a serious dermatitis from euphorbia sap, so I kept the gloves on. The cuts will seal over and I think the plant will do fine. With new potting mix, a little room for roots, some fertilizer and increased humidity indoors, I’ll see flowers by Thanksgiving.

The begonias led to a different kind of potting-up project. The stems rot and break off so easily. They thrive on neglect, it seems, and too much water (or rain) is deadly. Mostly they don’t mind being somewhat crowded, but they do need a little room to grow root hairs. So I attempted a combination of cutting back the leggy extensions, choosing the portion of the plant that is most solidly rooted, and moving it – carefully – to the next size up. Begonias thrived wonderfully in our hot, dry summer (as long as they weren’t baked in full day sun). The all-time begonia winner is still ‘Dragon Wing’ and all its offspring. It will be painful to clip mine back enough to fit into its designated indoor space in two or three weeks – they don’t like cold nights – but I know that it will flower well into winter.

What’s next?

It is way too soon to take most plants inside. The theory is: Wait until the outdoors feels about the same as the indoors, before you turn on the heat. Many plants react badly to rapid, extreme changes. I will leave the Christmas cacti outside until frost is imminent. I will also cut back some 6-foot plants to fit through my doors once again. But that’s for another day.

My coffee turned cold, and my office work never got done that morning. But how I enjoyed that first “Potting Up Day.”

Sally Cunningham is a garden writer, lecturer and consultant.

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