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Tuesday - August 04, 2009

From: Sonora, CA
Region: California
Topic: Compost and Mulch, Diseases and Disorders, Transplants, Herbs/Forbs
Title: Coreopsis failing to bloom in Sonora CA
Answered by: Barbara Medford

QUESTION:

My Coreopsis buds form and then die. Very few open. The plants are two and three years old, in a clay type soil. Is it possible they're getting too much water, and that is whats making the buds die and not open properly? I don't water them a whole lot, but being a xeric plant, I just wonder? Thanks!!

ANSWER:

There are 26 species of the genus Coreopsis native to North America, 9 native to California and none native to Tuolumne County. Coreopsis lanceolata (lanceleaf tickseed) is native to 2 counties north of Sonora, but that's as close as any of them come. We realize that you are probably not growing something that naturally sprouted up in your garden, but that you purchased, either in bedding pots or seeds. It just helps to give us a clue when something is not flourishing, without knowing what your soil or climate is, precisely. Since Coreopsis lanceolata is one of the more popular in the nursery trade, we will look at the growing conditions for it and see what we can find out.

Coreopsis lanceolata (lanceleaf tickseed) is evergreen, blooms yellow April to June and is 2 to 3 ft. tall. From our webpage on this plant:

Growing Conditions

"Water Use: Medium
Light Requirement: Sun , Part Shade , Shade
Soil Moisture: Dry
CaCO3 Tolerance: None
Soil Description: Sandy, gravelly soils. Sandy, Sandy Loam, Medium Loam, Clay Loam, Clay, Acid-based, Calcareous
Conditions Comments: Lance-leaved coreopsis is the most common coreopsis and is easy to grow. It is drought tolerant but is not reliably perennial. However it self-sows readily and can become weedy. The showy golden flowers are nice in a vase and are a popular plant for visiting pollinators. It should have frequent deadheading to keep it in bloom well into the summer."

It looks like it will grow in clay and can even become pretty aggressive. So, we have some questions for you to ask yourself in trying to figure out what is going on? Have the coreopsis ever bloomed in what you consider a normal way in the two to three years you have been growing them? If not, you got off on the wrong foot, or stem, as it were, from the start. It is a xeric plant, but most of the West has been having a record-breaking heat and drought cycle and this may be inhibiting the blooms. With clay soil and xeric plants, you need to be sure they have the water to survive, but that their roots are not standing in water. Addition of some organic material (compost, for instance) to clay soil before planting can make a big difference, not just in drainage, but in permitting the roots to access necessary trace elements in the soil. If you suspect drainage is the problem, try working some compost in the soil around the plants now, covering the area with shredded bark mulch, and see if you can cut down on the water.

Another thought is fertilization. Everyone is tempted to try to cure any plant problem with a quick dose of fertilizer. In the first place, a native plant in its correct habitat should not need fertilizer, it is already adapted to the dirt in which it is growing. You should never fertilize a plant that is stressed, which it sounds like yours is, and NEVER use a high nitrogen fertilizer. That is meant to encourage lots of green leaves, as in grass, and not blooms.

Beyond those comments, about all we can offer is to point out that the plant's normal blooming cycle is from April to June, but, as you saw in the Conditions Comments above, frequent deadheading will encourage blooming into summer. Deadheading encourages further blooming because a plant's prime object is to survive, which means reproducing, which means seeds, which means blooms. If the blooms are removed, the plant will try to bloom again until it runs out of energy. It takes an enormous amount of energy for a plant to bloom and set seed, and there are limits to how long it can continue.

If you have seen no insects that appear to be damaging the buds, about all we can suggest is to experiment and see if cooling the roots with mulch, and trimming off any undeveloped buds will help. Although this plant is not considered reliably perennial, you might take the opportunity this winter of digging up the clumps of plants, dividing them and, while they are out of the ground, amending the soil as suggested above.

From our Native Plant Database Image Gallery:

Coreopsis lanceolata