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What Are The Best Potting Soils for Dahlias, Lilies, and Begonias?

 

“What kind of potting soil should I use for Dahlias, Asiatic and oriental lilies, and begonias?” Question from Luciana of Portland, Oregon

Answer: Each flowering plant has some distinct needs when it comes to soil moisture, pH, and quality. The right kinds of fertilizers also help these flowers bloom at their best.

Soil and Fertilizer for Dahlias

Potted Dahlias need porous soil that drains well, holds moderate moisture and has a slightly acid to neutral pH (6.2 to 7). I recommend our Black Gold® All Purpose Potting Mix or OMRI Listed Black Gold® Natural & Organic Cocoblend Potting Mix, which is approved for organic gardening. Both potting soils have all the right characteristics. When picking a fitting fertilizer, choose one formulated for blooming plants. Proven Winners Premium Continuous Release Fertilizer is a good choice. Adding Proven Winners Premium Water Soluble Plant Food as directed will also help boost flowering through summer.

Soil and Fertilizer for Asiatic and Oriental Lilies

Lilies of all types grow best in soils that are well-drained and rich in organic matter. The ideal pH should be a little more acidic (5.5 to 6.5), but neutral soils are also tolerated. Once again, I recommend our Black Gold® All Purpose Potting Mix in addition to another of our OMRI Listed mixes, Black Gold Natural & Organic Ultra Coir, which is rich in organics but drains well. Here, it is best to choose a fertilizer specially formulated for summer bulbs. These tend to be balanced fertilizers with added bonemeal, and there are many fine choices on the market.

Soil and Fertilizer for Begonias

Fast-draining soils that are light and fertile are preferred by begonias. Their tubers or fibrous roots are prone to rot, so soils that hold onto water too well can be detrimental. Once again, a slightly acid pH (5.5 – 6.5) is needed. Black Gold® Natural & Organic Potting Mix is a good soil choice. Adding a little extra Black Gold Perlite for added drainage is also recommended. Proven Winners Premium Continuous Release Fertilizer helps boost flowering and performance in begonias. The occasional addition of Proven Winners Premium Water Soluble Plant Food will also help boost flowering.

Have a great gardening season!

Jessie Keith

Black Gold Horticulturist

Beautiful, Blooming, Cascading Begonias for Hanging

The Belgian ‘Double Apricot’ pendulous begonia is a showstopper.

By February, I am longing for some beauty when I look out of the window.  It’s the worst month of the year here in the Midwest, with its dead and bleak outdoors. So,  now’s the time I start dreaming of the flower beds and containers for the coming year. This year I plan to focus on cascading Begonias for my shade pots, window boxes, and hanging baskets, and there are several excellent choices.

Cascading begonias are derived from several different species and begonia groups, but all of them have one thing in common, cascading habits and beautiful flowers. The tender plants have succulent foliage and thrive if given regular water, well-drained soil, and season-long fertilization. Here are those that I plan to grow at my own home this year.

Angel-Wing Begonias

‘My Special Angel’ is a new angel wing begonia offered by White Flower Farm. (Image thanks to White Flower Farm)

Angel-wing begonias have both beautiful leaves and flowers. The leaf size depends on the variety, but all of them have a telltale wing shape. They are hybrids of the Brazilian begonia (Begonia aconitifolia) and the Lucerna scarlet begonia (B. coccinea ‘Lucerna’), which were first bred by Eva Kenworthy Gray in 1926. The progeny and descendants have since been called angel wing begonias. Many hundreds of varieties exist today. (Click here for a full account of angel wing begonia history.)

Angel wings are cane-type begonias, which means that they develop tough, almost bamboo-like stems called canes (click here to learn more about cane begonias). Their pretty wing-shaped leaves may be green, bronze, silver, or deep rose, and some are marked with lighted dots or stripes. The flowers appear in clusters over the leaves and come in shades of white, pink, orange, or red. Standard angel wing begonias can become quite tall (4 feet or more), without pruning, and are best reserved for large containers. To prune, cut back any tall or leggy stems at a leaf node.

The new variety called ‘My Special Angel‘ looks especially promising with its pink flower clusters and bold, beautifully speckled leaves. ‘Whimsy‘ is similar but has darker speckled leaves. Expect both to reach between 1 to 3 feet without pruning. Another exceptional variety is the bold, large-leaved, salmon-flowered ‘Snow Cap‘, whose leaves are olive-green and speckled heavily with silver.

Dragon Wing Begonias

Dragon Wing Pink begonias bloom all summer long. (Image by Proven Winners®)

Dragon wing begonias are also cane-types, but they are shorter, more compact, and better for hanging baskets. Most will cascade to 30 inches or less. Their leaves and flowers are equally as showy and diverse but often smaller. I have been wondering what to put in my large shaded baskets, and a dragon wing, such as Proven Winners® Dragon Wing® Red or Dragon Wing® Pink, would be perfect. Each has glossy green leaves and colorful, drooping flower clusters. They will look gorgeous. The plants are self-cleaning and should not require pruning.

Pendulous Tuberous Begonias

Illumination Orange Begonia is very pretty and can be grown from seed.

My favorite cascading begonias are pendulous begonias (Begonia pendula hybrids). They are best known for large, spectacular, single or double flowers, in many shades of red, rose, pink, yellow, ivory, and apricot, which cascade to 15 inches or more. Most reach 8 to 12 inches high. The double flowers look like roses! The plants are so impressive that I have ordered three this year, so my shade containers are going to be all begonias this year. One of the prettiest is the outstanding Belgian hybrid, ‘Double Apricot’. You can also try the beautiful varieties in the Illumination® Series, which can be grown from seed. (Always start begonia seeds as early as January to get them to planting size by May.) Illumination® White and Orange are especially resplendent.

Pendulous begonias are tuberous, so you can most commonly buy them as easy-to-plant tubers or as plants. Often the plants sold at garden centers are small, so you can put three of them in one large basket or pot.

Bolivian Begonias

Santa Cruz® is an exceptional Bolivian begonia variety with orange-red flowers. (Image thanks to Proven Winners)

Hummingbird-pollinated Bolivian begonias (Begonia boliviensis hybrids) have entirely different flowers than most other begonias. Each has five long petals, which form a single elongated flower. The green leaves are narrow and pointed. The stems hang at least 20 inches over the side of the container and can stand 1-3 feet high, depending on the variety. These are most commonly sold as plants, but they may also be purchased as tubers.  Santa Cruz® is an exceptional form with orange-red flowers. Several pretty hybrid mixes with many-colored flowers are also available. This is a small taste of the numerous varieties out there.

Planting Cascading Begonias

Begonias do best in shade but will tolerate partial sun–between 2-4 hours per day. As stated above, these begonias may be tuberous or have fibrous roots. Tubers need to be planted root-side down (often with the hollow-side up) and only 1.5 inches deep.  If small, pink buds are already emerging from the tubers, take care not to damage them, and plant with them facing upwards. Apply a continuous-release fertilizer at planting time. Begonias like organic-rich soil that is well-drained, such as Black Gold Ultra Coir Potting Soil.  Be cautious not to overwater pots because this can lead to tuber or root rot.  You can start growing them indoors to give them a head start for planting outside in late spring.

These begonias have gotten me excited about my potted flower garden plans.  Now I’m really looking forward to spring!

Wrap Up with Climbing Rex Begonia Vine

Climbing Rex Begonia Vine - Pam Beck
If allowed to grow outdoors in summer, the Rex Begonia Vine can reach 12-feet in height.

If you are excited by the prospect of growing a unique vine indoors, there is none more interesting than the climbing Rex Begonia Vine, Cissus discolor. The leaves of this quick-growing vine are deep green, decorated uniformly with silvery brushstrokes, and when flipped, the leaves reveal surprising burgundy-red backsides matching its stems and tendrils.

For the best results, give Rex Begonia Vine adequate support, allow it to dry slightly between waterings, and place it near your brightest windows. The best mix for this plant is Black Gold African Violet Mix.