The Dallas Arboretum plant trials program is a natural choice for breeders and plant promotion companies to test their materials. As all Texans know, we have one of the most extreme climates. It can be sunny and hot one day and freezing cold the next, or drought for six months followed by flood. Plants have to be tough to live here! Quite often I hear that this or that plant is heat tolerant because it survived 90-plus degrees in the north. Well my answer is always “90-plus degrees? Oh, that was our low temperature last night!” Our long growing season, hot summers, erratic winters and troublesome soils really puts plants through their paces. We test annuals, perennials, shrubs, trees and bulbs. Here are some of the best performers we tested this year.
ANNUALS – COOL SEASON
Pansies – When it comes to pansies, bigger flowers don’t mean better plants. We’ve found that the mid-sized varieties flower more, return faster after hard freezes, and last longer in the heat. The best performer historically is the ‘Nature’ series from Takii. This variety is one of my favorites, with compact plants, and 2-1/2 inch flowers in many colors that are held just above the 
foliage. The ‘Matrix’ series from PanAmerican Seed is another proven variety with excellent growth habit and heavy flowering. It comes in both solid color flowers and those with faces (or blotched as we call them in the industry). If you want a slightly larger flower, go for the ‘XXL’ from PanAmerican series. It is one of the few large flower varieties that scores highly for us.
If you really want a lot of color for your buck, then choose the smaller flowered violas. Believe it or not, but plant for plant vs. pansies they deliver more flower power! They show wonderfully from a distance because there are so many blooms. The best scoring varieties in our trials this year were the ‘Gem’ & ‘Jewel’ series from Takii seed, the ‘Gemini’ series from Sakata and the ‘Sorbet’ series from PanAmerican. Truthfully there isn’t a bad viola out there! They all perform wonderfully for us.
Dianthus ‘Amazon’ series from PanAmerican is my favorite dianthus. This one should be planted in fall. The deep green glossy foliage will form 12″ mounds that will erupt in spring with flower stalks that stand 2-1/2 feet tall topped with softball sized flower heads. Guaranteed to stop traffic. There are three colors available: Neon Cherry, Neon Purple and Rose Magic. The last one, ‘Rose Magic,’ may be the neatest flower ever; each head is composed of hundreds of small flowers of different colors. Yes, different colors of purple, pink, and rose. All colors of this variety make excellent cut flowers, too.
Snapdragons — There are many new choices in snaps. Some of my favorites are the old standbys ‘Liberty’ & ‘Sonnet’ series. Both of these get 2 to 2-1/2 feet tall with large spikes of flowers. All snaps really should be planted in fall. This will give them time to form large plants that will reward you with multiple flower heads next spring. Two new series that I really like are the ‘Solstice’ series from Ball Seed and the ‘Coronette’ series from Syngenta, both of these form 12 to 18 inch plants with large spikes of flowers that last for a long time. Neither needs staking to stay upright in our windy springs.
Columbine — Most parts of the world look at columbines as tough perennials for shade; unfortunately they are just not adapted as perennials in most of Texas (with the exception of the Texas native Aquilegia chrysantha ‘Hinckleyana’). Two series have stood out in our trials as fall planted annuals, the ‘Songbird’ & ‘Swan’ series. Both series come in multiple color combinations. My personal favorite is ‘Songbird Dove.’ Huge white flowers flutter of blue gray foliage starting in mid-April through May and are sure showstoppers in shade.
ANNUALS – WARM SEASON
Ageratum ‘Artist’ Series from Syngenta. OK, I was skeptical about this one. Ageratum just doesn’t live long in Texas, so the first time this series lived all summer through 100-plus degree weather I chalked it up as a mistake. Well it did it three years running! This is one tough plant, flowering from first planting in April until the first frosts of November. No other ageratum has ever even come close. It is available in blue, purple and rose. All do equally well.
Angelonia ‘Angelmist White Cloud’ from Ball Seed is a true improvement in Angelonia. I’ve never liked the fact that most Angelonia flop over and cycle in and out of bloom. Well, this variety stops all of those problems! ‘Angelmist White Cloud’ forms perfect 14-inch plants with tight flower spikes of purest white.
Begonia ‘Babywing Pink’ from PanAmerican is a heavy flowering dwarf form of the indispensable ‘Dragonwing Pink’ Begonia. The beautiful mounds of arching foliage are covered in light pink flowers. The 2-feet tall plants work wonderfully in shady borders and are much more compact than ‘Dragonwing Pink.’ Excellent planted in containers.
Celosia ‘Fresh Look’ was a surprise winner for me. This All-America Selections winner truly deserves its title. The plants are easily grown from seed and quickly begin to flower, and continue to flower all summer. Most celosia stop flowering quickly and succumb to our high heat, but not ‘Fresh Look.’ The 2-1/2 feet tall flame like plumes of red, orange or yellow stand out in the landscape.
Pentas ‘Graffiti’ Series from Benary. Pentas have come a long way in the last few years. Not too long ago pentas were available only in a few colors and were tall gangly plants that did not flower heavily. The ‘Graffiti’ series is destined to become a staple of Texas gardens. Easily grown in full sun or shade, the 12-inch tall mounds are constantly blanketed by large clusters of flowers. And like all pentas this series shrugs off our Texas heat and humidity and keeps on blooming until frost.
Torenia ‘Catalina’ Series from Proven Winners is my horticultural version of a slipcover. You have an ugly spot in the garden? Grab some Torenia! ‘Catalina’ series Torenia comes in several colors and will grow equally well in sun paired with lantana or mixed in shade with impatiens. This particular Torenia has large upright blooms that are produced on compact plants that spread to 2 feet No other summer annual gives us such rich purples and blues as Torenia.
Zinnia ‘Profusion’ Series from Sakata is guaranteed to fire up your garden with color! These are trowels down the toughest and most disease resistant ever. This hybrid of the tall cutflower type Zinnia elegans and dwarf small flowered Zinnia linearis combines the best of both. Large semi-double flowers on disease resistant 18 inch mounds are always in bloom.
My favorites are ‘Fire,’ ‘Orange’ and ‘Apricot’ all in lessening degrees of orange. ‘Profusion White’ is another that is also wonderful in the garden. I do not recommend ‘Cherry,’ though. The plants are disease resistant, but the lovely pink flowers become spotted with brown the first hot days of summer.
ANNUALS – FOLIAGE
A good rule of thumb when designing containers or annual color flowerbeds is to use about half flowering plants and half foliage. The combination of the two produces something much more beautiful than either one alone. Think of your garden as a cut flower bouquet, that backdrop of green, burgundy or variegated foliage acts as a frame for the flowers. Plus, even if for some reason your flowering plants stop blooming the foliage can still carry the show.
Ctenanthe lubbesiana ‘Tropical Dragon.’ Yes, I know this is a house plant! That should be a clue to you how tough it is. This fast growing tropical plant will quickly grow to 3 feet tall in the darkest shade areas. Heat, drought and humidity indifference are just a few of its good traits. OK, so it doesn’t flower, but the lovely shiny foliage is splashed with bright lemon yellow. Try it planted with white impatiens and the yellow spikes of lemon lollipop (Pachystachys lutea).
Coleus ‘Aurora’ series ‘Black Cherry’ & ‘Peach’ from Ball Floraplant. These coleus look good enough to eat! Wonderful splashed foliage on shorter compact plants will grow in full sun or shade. A perfect compliment to shade or sun containers.
Duranta ‘Gold Eagle’ has glossy green leaves centered with bright lemon yellow. This tough plant handles full sun or shade and loves our hot summers. Mix it with blue Torenia for an incredible combination.
Pepper ‘Black Pearl’ from Ball Seed has deep dark purple black foliage that stands up to the hottest summers Texas can serve up! If that’s not enough, each branch is topped with glossy black pearl-like peppers that age to scarlet red. These 2-1/2 feet plants are standouts in the landscape and look as good the last day of fall as they do when planted in spring.
PERENNIALS
Chinese Wild Ginger (Asarum splendens is one perennial no shade garden in Texas should be without. Its deep green leathery evergreen foliage looks so perfect, it almost seems fake. This plant is tough enough in the shade at the base of a Live Oak. Winter hardy through zone 6, this perennial is well worth the extra effort it will take to locate.
Begonia semperflorens ‘Kayleen.’ Yes, I did mean to put this under perennials. This particular bronze leaf begonia forms tiny bulbils at the base of the plant each year and is winter hardy through zone 7 in Texas. I’ve had it hardy in the trial garden for 3 years and my personal yard for 7. The burgundy foliage will begin to emerge in early April and is quickly adorned with typical pink begonia flowers. Plants perform best in full sun, but will survive handsomely in shade.
Dianella tasmanica may be the best thing to come out of New Zealand! This perennial has wide spike-like leaves of glossy green variegated with bright white edges. The 20-inch tall plants will grow in full sun or in bright shady areas. The flowers are not showy and almost grass like. I absolutely adore this perennial as a container plant. The upright spiky foliage compliments everything.
Blue Love Grass — Eragrostis elliottii ‘Wind Dancer’ from PanAmerican is a new blue foliaged grass that is perfectly adapted to Texas. The arching graceful leaves wave in the slightest of breeze enlivening any garden. The 4-feet tall mounds are great planted in mass and are exceptionally drought tolerant once established.
Salvia farinacea ‘Henry Duelberg’ was discovered by Greg Grant in a Texas cemetery. This vigorous 4-feet tall perennial is the heaviest flowering mealycup sage I’ve ever seen. The bright indigo blue flower spikes are produced from late spring until first frost. This Texas native is as tough as they come, but will reward occasional watering and fertilizer with constant blooms. Monarch butterflies adorn this plant every fall on their yearly migration. If white is your preferred color, try Henry’s wife ‘Augusta’ which has beautiful pearly white flowers.
Scoparia ‘Melongolly Blue’ from EuroAmerican didn’t impress me at first, but everyday I saw it just kept getting better and it never went out of bloom. This plant has wonderful soft textured light green foliage that is dusted with pure blue flowers. The cloud-like plants flower all summer. The small flowers and soft texture are best viewed in containers or planted where you can see them close up. The foliage was evergreen for us to 16 degrees.
The goal of the Dallas Arboretum plant trials is to find the toughest plants for Texas. We hope you will try some of these new varieties in your garden this year. Though some may not be easily available, keep looking because they are well worth the extra time to find them. If you would like to learn more about our trial program please visit our Web site at www.dallasplanttrials.org. Also, help support our test garden by coming to our 2nd annual plant sale on April 22-23.