Rudbeckias and sunflowers are late summer's gold in Sonoma County

Despite the oppressive heat of late summer, when we all wilt, the brilliant yellow daisy flowers called black-eyed Susan’s (Rudbeckia) and annual sunflowers (Helianthus) are in full glorious bloom, defying the long days and warm temperatures.

The vitality of the blooms seem fed by the sun itself. There are a number of showy rudbeckias and sunflowers that grow well in the area.

Rudbeckias and sunflowers are in the sunflower (Asteraceae) family. The flowers of many plants in this family are composed of showy ray flowers - the petals and the less spectacular but very interesting central disc where the flower reproductive parts are contained. For a bee, the disc is where the action is.

The petals that we so admire serve only as nectar guides to the pollen and nectar contained in the multitude of tiny disc flowers clustered together. Tiny, individual disc flowers bloom starting from the base or outside of the disc, and gradually over a period of days, progressing up to the top or middle of the disc. As the tiny flowers mature, you can see bees working upwards or towards the flower middle to gather pollen and nectar.

The most common rudbeckia is the perennial Rudbeckia fulgida ‘Goldstrum.’ It is a long-blooming, easy-to-grow plant that spreads over time by rhizomes. The leaves and plant are deep green, compact and usually stiffly upright to about 2 feet tall. The central disc is black - hence the name, and is a distinct raised button. The petals are positioned downward. This floral arrangement is typical of many rudbeckias. The speed of spread depends on conditions. With lots of water and good soil, the spread is faster. With dry conditions and poor soil, the spread is slow.

If you desire a large swath of showy, bright yellow daisies this plant is a good choice. Cut spent flowers stalks down to about 1-3 inches above the ground to stimulate more bloom. This rudbeckia is not the best for bees.

Another rudbeckia less commonly seen and a little less easy to accommodate in gardens due to the plant’s size is Rudbeckia nitida. It has much larger, more loosely held, coarse toothed leaves.

The flowers are at the top of 7-foot tall rather loose stalks. The petals are a clear bright yellow, and slightly limp, hanging distinctly downward.

The central disc is green, becoming gold, as the tiny flowers mature.

The cultivar R. nitida ‘Herbstonne’ has larger flowers with more broad petals. This rudbeckia spreads too, but more slowly than the R. fulgida.

With lots of water and compost, the ‘Herbstonne’ cultivar may need staking. This rudbeckia is highly attractive to both honeybees and native bees and is a great place to observe them. The species also grows well with some shade.

A really perfect rudbeckia is Rudbeckia triloba. It is a short-lived perennial from the Midwest, and reseeds a little each year. It closely resembles a very densely branched dwarf sunflower.

It grows to about 3-feet tall and is covered in a multitude of sunflower-like flowers for weeks starting in midsummer through fall.

Incessantly cheerful and well-behaved - this rudbeckia should be more widely grown. This rudbeckia is highly attractive to bees. It is drought resistant but also grows well with regular water.

Rudbeckia hirta or gloriosa daisy is usually grown as an annual but is a short-lived perennial. It is about 2-feet tall and has very upright stiff, hairy stems and leaves with huge daisy flowers from deep orange-yellow to multi-colored shades of brown and red.

The leaves are large and lance-shaped. It makes great cut flowers and is very drought resistant. It can reseed. Cut spent flowers down to a low branch junction to stimulate more bloom.

Helianthus annuas, the annual sunflower is both wild and planted in the area. Surprisingly tough, it grows along roadsides and in grassland. In gardens, both multi-branched and single-stem cultivated varieties are planted.

Flower colors range from traditional yellow to peach, red and multi-colored blooms. Plant size depends on the soil, water and nutrients they receive, but many varieties are around the 6-8 foot range. There are dwarf varieties available.

Dwarf varieties often bloom for a very much shorter period than large sunflowers and may not be worth planting. Some sunflowers are bred to be pollenless.

Initially a genetic mutation, they are now grown extensively for the cutflower trade as blooms won’t drop pollen onto your table.

While convenient for us - this is bad news for bees. While these varieties still produce nectar - a bees daily fuel - pollen is a larval food source both for our native bees and honeybees. No pollen means no bee reproduction. Sunflowers are a very important summer pollen (and nectar) resource for a variety of native bees, some which specialize in this pollen, and for honeybees for their brood.

Also, sunflower seeds are rich in proteins and fats for songbirds. Pollenless sunflowers generally produce few seeds.

For those who enjoy starting plants from seed, the annual Silver-Leaf Sunflower (Helianthus argophyllus) a native of Texas, Florida and North Carolina, is a spectacular annual sunflower.

It is a 6-foot tall and 5-foot wide multibranched sunflower with mid-sized leaves and dense growth. Branching is robust and begins at ground level. The soft silvery/white foliage is what sets this sunflower apart - and the leaves and stems are covered with silvery, fine hairs.

The multitude of flowers are 6 inches across and are a deep yellow with a chocolate-colored central disc. It is very heat- and drought-resistant and needs full sun and well-drained soil. Drip irrigation is best. Too much water causes the branches to break.

Annie’s Annuals and Perennials (anniesannuals.com) usually has plants early and though spring. The seed company Select Seeds (selectseeds.com) sells the seeds as Sunflower ‘Gold and Silver’.

Kate Frey’s column appears every other week in Sonoma Home. Contact Kate at: katebfrey@gmail.com, freygardens.com, Twitter @katebfrey, Instagram @americangardenschool