Not too long ago, a reader emailed me and asked,

I bought some hostas and dwarf bleeding hearts to plant. Shortly thereafter I hurt my knee and I can’t go out there and plant them. They are all planted in one gallon plastic pots. How can I safely winter them? If I put them in my garage they will still freeze.

You may have plants in containers that should have been planted, but weren't. How do you winter them over?

It is the roots you are worried about freezing. The rule of thumb is that roots in a pot will effectively be in a situation two zones colder than plants in the ground. So if the plant tag says zone 5 and you are in zone 7 they should be fine.

But I’m guessing you live in a colder place. Definitely keep them outside until the tops die down. You want them to go dormant. After that, you want to put them in a situation where they will stay dormant but not get colder than two zones warmer than the hardiness zone on the tag. That will be different depending on what is available at your place. The garage might be okay, if it gets cold, but not as cold as outside. You could put them up against the house, and surround them with bags of leaves for insulation.

The other thing to consider is the greater the volume of soil in the container, the more insulation the roots will have. A one gallon container is not that big, and won’t have much insulating soil mix for the roots, so you might err on the side of caution and make that three zones warmer than the tag.

I have a drafty, dirt floor cellar that barely stays above freezing. I have put dormant plants in the coldest corner of the cellar and pulled them through the winter. They did start growing sooner than they should have, and made some pale spindly growth, but I very carefully hardened them off and planted them after all danger of frost. It was a pain in the neck but better than losing them.

Most herbs taste much better fresh, and rosemary is no exception. That’s why every winter I try to keep my rosemary alive in a pot inside the house. Rosemary is not reliably hardy north of zone 7, so while southerners can grow this in the ground and watch it take on shrub-like proportions, we cold climate gardeners must bring it into our houses and attempt to give it the equivalent of a southern winter indoors, or it will never really get big enough to harvest from regularly.

It’s not easy, let me tell you. More than one northern gardener has finished the winter with a dead rosemary plant. To succeed with any plant, a gardener thinks about its native range and tries to approximate those conditions. Rosemary is native to the Mediterranean basin. This is where many people make their first mistake. They hear that rosemary is drought-tolerant, and they let it dry out. But as Nancy Szerlag, Detroit News gardening columnist states, “a dry rosemary is a dead rosemary.” What people forget is that the Mediterranean climate receives almost all its yearly precipitation during the winter. The rosemary wintering over on a windowsill still expects it to rain.

That same Mediterranean native thinks winter is significantly cooler than the typical furnace-heated northern residence. Judy Miller, owner of Paradise Gardens Rare Plant Nursery and occasional contributor to this website, says, “I either keep it on a barely heated sunporch so it doesn’t go below freezing or above 50, or against the coldest window in a cold room.” No habitable room in my house stays below 50F in the winter, but some rooms are definitely cooler than others. Those are the rooms I consider for the rosemary.

This 8 year old 'Salem' rosemary is over 3 feet tall and wide. It spends each winter indoors. Photo by C.L. Fornari.

This frost damaged rosemary gives you an idea of how large my rosemary had gotten after two years. Unfortunately, all the leaves dropped and one whole section of the plant never came back after it was subjected to a late spring freeze.

Where to find named cultivars of rosemary

You can find rosemary in the spring almost anyplace that sells vegetable seedlings. However, if you want to get a specific cultivar, such as ‘Salem,’ you will probably have to order through the mail. Papa Geno’s Herb Farm has an extensive selection of rosemary varieties, including ‘Salem.’ I’ve never tried them myself, so if you have experience with them or have your own favorite source to recommend, please tell us all in the comments.

Improvisational Container Planting

I am pretty lackadaisical when it comes to container plantings. I have three window boxes hanging on the porch fence-cum-railing and a rusting metal washtub that I found in the barn when we moved in. I never really plan or purchase plants for these containers. I count on something showing up due to the kindness of friends or excessive seed sown, and then I try to make it work. Let’s call it improvisational container planting to give it some credibility. (Click all photos for larger–and sharper–image)

Take me to your secret garden

The washtub container used to rest by the main entrance to the house, but last year I moved it to the entrance to the Secret Garden, because we don’t want the Secret Garden to be so secret that no one finds it, right?

This photo is looking north. The house is downhill to the west, or to your left. The branches of the apple tree obscure the planter from the house more than they did last year, when this photo was taken.

So I wanted something bright for this container to be visible from the house, drawing you to investigate. That was the plan, but now that the apple tree is fully leafed out, you’re lucky to catch a flash of red when the wind ruffles the leaves.

Oh well. The red flower underneath the zonal geranium (aka pelargonium) is Tukana Scarlet Star Verbena, and the one below that with red and orange florets is Luscious Citrus Blend lantana, both received from Proven Winners as trial plants. I’d only grown verbena once before, and lantana never, so I was pleasantly surprised at how well they’ve been doing, especially since I never water the container. Well, I probably watered it once or twice after it was first planted, but never since. Out of sight, out of mind. That marigold blooming like crazy is ‘Signet Starfire’ from Renee’s Seeds, also a trial. And the geranium was given to me without a tag. Generic geranium. This container doesn’t follow the thriller, filler, and spiller formula, but it is bright.

Mother’s Day Special

Another tradition traditionally ignored around here is buying Mom a present for Mother’s Day. (Buying being the operative word, as plenty of homemade gifts and donated labor abound.) This year tradition was impulsively tossed aside by my DH, and I was escorted around the local Lowes with the injunction to pick out anything I wanted. Anything. Talk about brain freeze! I finally settled on a lovely hanging basket, suppressing both the gasp as I looked at the price tag and the frugal urge to put it back and look for something more reasonable.I think pale yellow flowers, such as this Yellow Chiffon Superbells calibrachoa, complement many hues on the color spectrum, especially the true blue of the Laguna Sky Blue lobelia, both, again, from Proven Winners. Just looking at this makes me sigh with pleasure, even though I know it is unfashionable in some quarters to love pastels. I think three windowboxes filled with this combination next year would not be too much.

Another good choice for containers, beds–and vases

Unless, that is, I decided to fill it with the Supertunia Vista Silverberry petunias above, accompanied by the Laguna Heavenly Lilac lobelia on the other side, pictured below. (Both were trial plants from Proven Winners.)This year the window box also has Gulf Winds alyssum provided by Renee’s Garden and Balcony petunias purchased as seed from Select Seeds. The Balcony petunias are wonderfully fragrant in the evening, but we only figured out after this photo was taken that they need to be pinched back regularly to look their best.

Next year, I would just use one Silverberry supertunia with a Heavenly Lilac lobelia on each end, and plant the Balcony petunias separately. The Silverberry petunia can also be a spectacular groundcover as you can see in Flowergardengirl’s North Carolina garden. One reason my Silverberry doesn’t look as full is we’ve discovered these petunias make excellent cut flowers.They last a long time in water and continue to open new buds. According to the literature I received, the “blooms are silvery white in the heat and blush pink in cooler temperatures,” so those of you with warmer summers might not see as much pink in the blossoms.

The opportunity to trial plants and seeds (as a result of attending the GWA symposium last year) combined with my 17-year-old son working for a local wholesale greenhouse made this the best year ever for my container plantings. What was your most successful container planting this year?

I don’t plant/dig/plant the rosemary plants I winter over–I feel it is too hard on them to repeatedly re-establish. So I keep them in pots, large enough for them to be comfortable in and small enough for me to winter inside feasibly. And carry! This also allows me to indulge in pretty pots for the porch. To harden them off, I start trooping them in & out about now so they spend some cool rainy days outside, then brighter sunny ones, then maybe not bringing them in overnight after a week or so. But as we can have sharp frosts (20’s or less) right into June I never put them farther than an arm’s reach from the door so I can snatch them back in even if I’m on my way to bed when I look at the thermometer. After a few weeks they don’t mind the frost and I can relax. I’ve even had lemon grass come back after a 26 degree night! Now I don’t put the tropicals out until June. I got a lemon & a blood orange plant this winter and they will go out on the porch with the other babies this year. The lemon is flowering now and it is glorious!

Correction to the rosemary hints. They can freeze–just not way deep like you’d get outside. I think something like 10F is the limit, maybe 15? Does your porch get colder than that? (Prescott AZ where I saw the planters full certainly sees that cold in the winter. They have some snow now.) And keep the plants on the dry side.
As to germination requirements, the wonderful pages from Tom Clothier and Norman Deno’s books are huge, HUGE resources and I wouldn’t be without them. I am always finding some lovely thing I want that won’t germinate easily and they are my two best places to look.
Garden chores for today: snowshoe 1/2 mile to the mailbox to check for seed catalogs and shovel around the greenhouse. Next time it is above freezing I’ll check the pots in there for watering. I keep them on the dry side too as a little water goes a long way when everything is cold. I lose more pots to wet over the winter than I ever do to cold.
Does Talitha ever grow Cardoon? I have read that the shoots taste like artichokes and wonder if that’s true or simply wishful thinking!

Kathy, if you want to keep rosemary happy in the winter, keep it cold & bright (as if it were having a milder winter than you are!)–I either keep it on a barely heated sunporch so it doesn’t go below freezing or above 50, or against the coldest window in a cold room. They seem to need about 6-8 weeks of this type of cold, and probably short days/long nights to initiate flower buds, so natural lighting is best. Last winter’s cuttings, now in 4″ pots, are all blooming as well so I think it is conditions more than age that favor bloom. Interestingly, different varieties are more precocious than others–I have an upright one that didn’t bloom last winter but is budding now. If you bring the plant into a warm room to show off this will shorten its blooming time; I bring some into the house at Christmas but put them back on the porch at New Years.
This spring I will add a deep blue flowering variety, a pink flowering one (Pink Majorca), and maybe a red one. I am of two minds about ‘Arp’ which is reportedly the hardiest–I think it is ugly–mostly naked stems like a Charlie Brown Christmas tree. People would probably buy it because of its reputation but I would have a hard time recommending it. It also doesn’t have a good scent. Both Richters and The Thyme Garden have very nice assortments of rosemary.
One spring I was visiting in northern Arizona and many of the homes and businesses had planters and window boxes full of blooming rosemary–made me very jealous!