No matter how carefully I plan, no matter how perfect the growing conditions, it’s inevitable that I find gaps in the garden in late summer. Clearly, I’m not alone, or there wouldn’t be such a market for potted mums in September. Thing is, it’s tough to find holes exactly the right size for big potted fillers, and the dense, mounded form of container-grown mums make it hard to have them look loose and comfortable, instead of like blobs dropped into the garden. With a little advance planning, annuals can be a much better-looking option for filling spaces and adding fall color.
I’ve found that early to mid-August is the ideal time to give the garden a thorough grooming and then tuck annuals into the holes left by weeding and cutting-back. The only way to have fresh-looking fillers on hand at this time is to start them myself in July. And now that I’ve gotten more into vegetable gardening, it’s easy to think about starting annuals at the same time I’m sowing kohlrabi, broccoli, cabbage, lettuces, and other veggies for fall.
I used to just start whatever seeds I had left over from spring, and I still do that to some extent. But I also like to look for good sales in early to midsummer, when retailers are trying to clear out their spring seed racks. Even better are the fillers that I can easily root from cuttings of plants I already have. Set out in late summer, the seedlings or rooted cuttings have a few weeks to settle in and mingle with their companions, adding a lusher look to the garden.
So, what makes for good fall fillers?
For one, they have to sprout (or take root) and look good quickly. Started in pots in early July, purple basils such as ‘Red Rubin’, ‘Osmin’, and ‘Purple Tulsi’ are one of my favorites for August and September color.
The down side is that they’re very cold-sensitive, so they look pretty scrappy as soon as nights get chilly.
Coleus (Solenostemon), such as ‘Oxblood’ (above) and ‘Sedona’ (below), are also great for fall foliage color. In just two weeks, cuttings can root and produce a nice-sized filler plant for the front to middle of a border.
The same goes for ‘Purple Lady’ beefsteak plant (Iresine) [above], though it’s more of an spreader than an upright grower. That makes it ideal for sprucing up the edge of a border.
Sweet potato vines (Ipomoea batatas) root even more quickly than coleus and beefsteak plant. In fact, I often find pieces that have already taken root in my bark-mulched paths when I trim back some of the over-enthusiastic patches in August. If the weather is going to be cloudy for a few days, I transplant them directly to fill bare spots; otherwise, I put them in pots for a week or so before planting them out.
It takes them several weeks to thicken up and start vining again, so they’re not ideal for filling in along the front of a border (unless maybe you plant several cuttings in each pot to create a thicker clump). They are terrific for filling in around the base of upright perennials that have lost their lower leaves, or that have needed to be cut back.
‘Homestead Purple’ verbena is another trailing filler that’s super-easy to propagate from cuttings, or from stems that have rooted where they touch the ground.
Wandering jews (Tradescantia zebrina) are even easier than sweet potato vines: I just snip off shoot tips a few inches long, scratch up the soil a bit in a new spot, and keep the soil moist for a few days to let them root. They’re much more diminutive than sweet potatoes, so they’re ideal for small spots. I found one this spring that’s a solid deep purple, but the silver-and-green, white-and-green, and white-, pink-and-green ones are equally pretty and just as easy to propagate.
Most of the fillers I use for fall are low-growing trailers and weavers, but some of them are a bit taller for height or bulk. Cosmos – both Cosmos bipinnatus and C. sulphureus types – are ideal for this, easily reaching at least 2 to 3 feet in fall from a mid-July sowing and mid-August transplanting.
‘Tiger Cub’ corn (Zea mays) also reaches about 2 feet tall, and it has showy, white-striped foliage. It’s a simple matter to direct-sow the kernels in early to mid-July and enjoy the clumps of strappy foliage through September.
I have one tough spot in the front garden where a species peony fills a space about 3 feet across until mid-August, when it suddenly turns brown and goes dormant, leaving a huge empty space by late August. This year, I solved the problem by starting bed-of-nails (Solanum quitoense) from seed in early July, cutting back the other stems of the peony, and then setting out the solanum seedlings around the edge of the clump. They grew quickly and filled the space just as the remaining peony stems died back.
So, fast-growing is good when it comes to fall fillers, but it’s even better when they’re plants that actually thrive in cooler temperatures. That way, they just keep getting better as the autumn progresses, even if we get an early light frost.
Nasturtiums (Tropaeolum majus) are one of my top favorites for fall fillers. This year I sowed two flats (36 pots) of various nasturtiums in mid-July and could have easily used twice as many. Planted out in mid-August, they’re looking lush and lovely now in late August and are beginning to flower. They look much better than the ones I’d set out in spring, because those plants really fried during our hot, dry spells.
Pot marigolds (Calendula officinalis) are also winners for the same reasons: they’re super-easy to start from seed, grow quickly, come into bloom when still fairly young, and keep flowering freely as the weather gets colder.
While I’m sowing seeds for the vegetable garden, it’s a simple matter to sow extra chards (such as the ‘Bright Lights’ seedling above) and lettuces for fillers in the ornamental borders, too.
Best of all, though, are the annuals that serve as fall fillers all on their own, with no extra work on my part.
Just when I think I’ve lost them, seedlings of my favorite green flowering tobacco (Nicotiana ‘Ondra’s Green Mix’) start appearing throughout my borders in late July through August.
‘Cramer’s Plum’ love-in-a-mist (Nigella damascena) is another dependable self-sower. The seeds that overwinter sprout early, producing their white flowers mostly in May, followed by the plum-purple seedpods. In July, I crumble the dried seedpods around the garden, and by mid-August, a new batch of seedlings appears for fall color.
A few other self-sowers that help to spruce up the fall garden include dill (Anethum graveolens)…
…borage (Borago officinalis)…
…Brazilian vervain (Verbena bonariensis)…
…‘Kingwood Gold’ jewels-of-Opar (Talinum paniculatum)…
…silver ponyfoot (Dichondra argentea ‘Silver Falls’)…
…sunflowers (Helianthus annuus)…
…and celosias (which often produce some really wild-looking offspring).
Wow, that’s a lot of options for fall color! Who needs perennials, anyway?