Angelonia is one of those warm season annuals that can actually survive through winter as a pernnial to bloom again next spring. It may even want to continue to bloom untill frost. The flowers can be blue, purple, red, pink or white, and look something like small snapdragon flowers. Most have spots or stripes of an alternate color or two in their throats. Some modern varieties have fragrant flowers. Plants can get a foot or two tall, and almost as wide. In sheltered spots, angelonia can be cut back as soon as it starts to look tired in autumn. Exposed plants might be happier if cut back significantly later, as winter ends. Old growth may be unsightly for a while, but can protect interior stems and roots from frost. Besides, pruning stimulates new growth that will be more susceptible to subsequent frost.
Actually, French marigold, Tagetes patula, is no more French than African marigold is African. All are from Mexico and Guatemala. They were merely popularized and bred respectively in France and Africa. There are now hundreds of varieties. Yet, their color range is surprisingly limited to hues and shades of yellow, orange and ruddy brown. White marigolds are really just very pale yellow.
While African marigold is only occasionally grown for bigger cutting flowers on taller stems, French marigold is much more popularly grown for late warm season annual color. Because it blooms late in summer and early in autumn, and continues only until frost or sustained rain, it is often planted if earlier warm season annuals deteriorate while it is still too warm for cool season annuals.
French marigold can get more than a foot tall, and almost a foot wide, but typically stays closer to the ground. The delightfully aromatic and intricately textured foliage is rich dark green. Removal of deteriorating flowers (deadheading) promotes continued bloom, although a few spent flowers might be left to produce seed. Mildew can be a problem if watering is excessive or late in the day.
Like gardenia, dogwood and snapdragon, the potentially finicky Madagascar periwinkle, Catharanthus roseus, is often challenging to grow. It enjoys, but seems to prefer more humidity than it gets here. The happiest plants can get nearly two feet tall and wide in sheltered and humid spots. (They can get even larger in exposed spots in humid climates.) Yet, most of us are satisfied with relatively scrawny plants less than half a foot tall.
Madagascar periwinkle is popularly grown as a warm season annual until the weather gets too cool in late autumn, but it can tolerate a bit of cool weather, and can even survive as a perennial through winter if sheltered. The one or two inch wide flowers have five petals and small red centers, and can be white or various shades of pink, pinkish red, lavender or pastel orange. All parts of Madagascar periwinkle are incidentally toxic.
A landscape designer would have more fun describing both the modern and the good old fashioned varieties of morning glory. Their vivid colors are so resplendent. Their rich green foliage is so luxuriant. Their delicate vines are so elegant. Hey, perhaps this is not so difficult. Anyway, the popular garden varieties of morning glory are descendents of various species of the genus Ipomea.
Except for a few obscure types, and the perennial blue dawn flower, popular garden varieties of morning glory are surprisingly complaisant annual vines, which grow from seed sown at the end of winter. Without getting too invasive or weedy, they sometimes reseed where they get watered, although they might revert to a more feral state after a few generations, or after the first generation.
Some varieties of morning glory have the potential to reach single story eaves, although most stay a bit lower, and some varieties do not get much higher than a doorknob. They work well on small trellises, or even simple stakes, and are just right for picket fences. The simple two or three inch wide flowers are rich hues of blue, purple, red, pink and white, some with spots, stripes or streaks.
It is fair to say that garden verbena, Verbena X hybrida, is a reliable warm season annual. It gets planted in spring to spread out and bloom through summer with bright pink, red, purple or almost blue, or softer pastel pink or pale white. It is commonly replaced with cool season annuals by late autumn. However, garden verbena is actually a short term perennial that can survive winter to bloom for a few years.
Perhaps individual plants do not last long enough to be practical as permanent ground cover. Yet, if mulched just so, the thin branches can root where they touch the ground, and then grow into new plants to replace the original plants before they die out. Stems do not spread or cascade much more than a foot from where they are rooted. Nor do they stand more than six inches deep.
The flowers may not last very long once cut, but cosmos, Cosmos bipinnatus, blooms so abundantly, that there might not be any shortage of new flower to cut and bring in to replace those cut a day or two before. Their pastel pinks and lavenders, as well as white, suit the Easter season perfectly. Their soft light green foliage is remarkably lacy. Mature plants are about two to four feet tall.
‘Seashells’ has distinctively tubular petals (which are actually ray florets around the perimeter of each composite flower). ‘Daydream’ flowers each have a typical yellow center surrounded by a pink inner ring, which is surrounded by a lighter outer ring. ‘Sensation’ is a mix of tall varieties. ‘Versailles stays less than three feet tall. The popular ‘Sonata’ series stays less than two feet tall.
Cosmos likes full sun, somewhat rich soil, and regular watering. If it is happy enough, it can self sow.
Pulling out cool season annuals that are still somewhat colorful is never easy, even if they are already deteriorating. There is always the desire to stretch their season as late as possible until they succumb to warmer weather. Only a few can perform all year, or get cut back to hide below other taller plants until the weather gets cool enough in autumn for them to regenerate and bloom again.
Regardless of all the resistance, removing the annuals of a previous season relinquishes space for annuals that are appropriate to the next season, whether cool to warm season, or warm to cool season. Even if new annuals are initially wimpy relative to the older annuals that were removed, they should proliferate and bloom better than lingering unseasonable annuals would if not removed.
Timing is somewhat important. There is no point in removing cool season annuals too early if the weather is still too cool for warm season annuals. However, there is no point in planting too late either. Delayed planting only delays growth and bloom. Some warm season annuals, especially those grown from seed sown late in winter, prefer to get established while the weather is still cool.
French marigold is probably the most traditional warm season annual for bright yellow, orange and bronze. Lobelia contrasts excellently with rich blue and purple, and can also be purplish rose or white. Petunia can do even more with brighter and more variable colors. Cosmos provides pastel pinks and white on taller plants. Cockscomb colors rival those of marigold, and can also be red.
Pincushion flower, annual statice and zinnia are popularly enjoyed as bedding plants, and also work well individually, behind lower bedding plants, or in planters of mixed annuals or perennials. Verbena and moss rose cascade nicely from such mixed planters. Sadly, brightly colored and formerly popular busy Lizzie (impatiens) are either rare or unavailable because of a mold disease.
Nasturtium and alyssum are warm season annuals that are often grown through winter as well. Where they are allowed to naturalize and bloom throughout the year, deteriorating old plants might need to be groomed out as they get replaced by self sown plants. New nasturtium should be sown as seed, instead of planted as seedlings from cell packs. Alyssum grows well by either means.
The same cooling weather that is initiating fall color is what finishes the zinnias that bloomed so colorfully through summer. Like tomatoes, they can stay out in the garden until they succumb frost if they continue to perform, and if the space they occupy is not needed for something else. There should be no guilt with replacing them sooner. After all, they are technically warm season annuals.
Some of the more popular types of zinnias are identified as Zinnia elegans or Zinnia violacea. Most are known merely by their variety name. They have been bred so extensively than it is difficult to assign any of them to particular species. Most are susceptible to mildew if crowded or watered from above. They want full sun exposure and rich soil. Seed can be sown immediately after frost.
Zinnias are crazily variable. Some get more than three feet tall. Others are less than a foot tall. They can bloom in every color except blue. Some resemble other types of daisies, with distended centers. Others are as fluffy as African marigolds. Some bloom with small but profuse flowers. Others have fewer but bigger flowers that are wider than three inches. Most are excellent cut flowers.
It is pretty but pervasive. Actually, I do not really find scarlet pimpernel to be all that appealing, but this is how someone who reads my gardening column in the Santa Ynes Valley News describes it. Embarrassingly, she requested that I discuss scarlet pimpernel while it was more of a problem back on June 7, but I only recently read the message. By now, it is already dying back for autumn, and is completely deteriorated in dry and hot exposed areas. It will be back next spring, and will bloom with tiny peachy orange flowers so that it can throw tiny but ridiculously abundant seed by summer before anyone notices. Flowers can be other colors in other regions. The sprawling stems can spread more than a foot wide, and can get up to about ten inches high if sprawling over other weeds. The tiny and soft leaves are arranged in opposing pairs. Scarlet pimpernel may not seem like much of a threat now that it is deteriorating, but new seedlings will be profuse early next spring, and can compete with seedlings of more desirable plants.
Control of scarlet pimpernel is not easy. If application of herbicide is an option, it does not stick to the foliage of scarlet pimpernel very well, even with a wetting agent. Hoeing eliminated larger plants, but does not kill the seed that the larger plants have already tossed. Scarlet pimpernel starts throwing seed so early that it must be pulled as soon as it appears in very early spring. Like I said, it is not easy. The small plants are not even easy to see. The process must be repeated at least weekly for a while, just because some seedlings will emerge after the first batch is gone.
Fortunately, scarlet pimpernel is not very vigorous. If it comes up through mulch, only a few plants will survive, and they will be easy to pull. They do not compete with other more vigorous plants well either. Many simple ground covers will simply shade it out, although it can mingle with and ruin some of the finely textured ground covers like baby tears and thyme.
I am sorry that I do not have any more information about scarlet pimpernel than is commonly known. I am speaking primarily from experience, and my experience has not been as bad as with other more aggressive weeds. Scarlet pimpernel always seems to be around, but is not so much of a problem that I am too worried about annihilating it completely.
Good old fashioned busy Lizzie is hard to find nowadays, if it can be found at all. The nasty mildew that kills it so quickly might not be prevalent everywhere, but happens to be a serious problem where most of the bedding plant farms are located. Now, the formerly uncommon New Guinea impatiens, Impatiens X hawkeri, which is somehow resistant to the mildew, is becoming popular.
The two specie have distinct personalities though. Busy Lizzie dazzles with cheery cartoonish colors, and bloom profuse enough to almost obscure the light green foliage. New Guinea impatiens has bigger and bolder flowers of white, pink, red, magenta, lavender, purple, apricot and reddish orange, but does not try to hide its rich green, bronze, purplish bronze or gold variegated foliage.
New Guinea impatiens are more expensive, and are not available in cell packs like most other bedding plants are. They are most popular in four inch pots. They do well in pots and tolerate partial shade, but want rich soil and regular watering. Mature plants can get more than a foot wide, and might get as tall if crowded. Although grown as annuals, they can survive as short term perennials.