Vinca rotting and dying off, how to treat and save the plant

Rotting and wilting vinca flower

Though it loves water, in cases where drainage is bad you’ll have to fight off root rot because your Vinca is dying and rotting away!

In this page, we’ll take a look at the symptoms of diseases that tend to make Vinca rot, and work out how to save your flower bed from going bare.

  • Shown right: sick Vinca minor

What causes root rot on Vinca?

Even though its native environment is along river beds, Vinca is still a plant that can die due to too much water. Whenever drainage is poor, water sits and roots can’t breathe. Fungus start developing, and ultimately they spread to the whole plant which dies.

Some modern varieties are bred to resist disease to a certain point, but it hasn’t been a strong focus of breeders to protect plants beyond the nursery stage yet.

There are four possible fungus that cause root rot in Vinca, to wit:

  • Pythium
  • Phytoptora
  • Thielaviopsis
  • Rhizoctonia

They’re all commonly dormant in soil, and it usually takes bad growing conditions to trigger them:

  • Clay soil (usually heavy)
  • Low drainage, water sits instead of seeping in
  • Overwatering
  • Planting too close and too dense (low air circulation)
  • Both summer heat and high air moisture occurring together

Before going into the disease itself, at this point you should know that it’s still OK to take a few cuttings of the healthier parts of the plant. If well cared-for, they’ll make for new if all goes awry!

Different root rot types on Vinca

All four of fungus listed above usually lie dormant in the soil (Thielaviopsis is a bit rarer than the very common other three). When conditions trigger them to spread, they compete to colonize the sick vinca plant and usually only one of the fungus “wins”. It’s rare to see a plant extensively infected by more than a single type of fungus, usually it’s a “one or the other” situation.

Symptoms of a Pythium infection on Vinca

Along the green stem, black veins start appearing, sometimes spreading to the leaves, too. If you cut a sick stalk at this point, you’ll notice the stem is dotted with black spots. These are sap channels infected with the black fungus. Alongside are usually a few remaining healthy sap veins.

The plant rots from the ground upwards.

Phytoptora root rot symptoms on vinca

Black or brown spots appear on the stem. They clog all exchanges between leaves and root system. As a result, the portion of the plant above the spot quickly dies off, whereas other stems still look healthy. When the entire root system is infected, the plant turns yellow and brown. Leading to this point, you might notice growth is slow or stunted compared to healthy plants. Pulling a plant out, the thin woody part of roots remains, but all the soft root materials is decayed and easily removed.

Symptoms of Rhizoctonia root rot on Vinca

Plants first start yellowing, and then collapse as the fungus destroys the internal structure. Roots themselves don’t rot as for the other fungus, but they still show wounds and bulges that a healthy plant doesn’t have. Your vinca will wilt despite water being everywhere around them.

Thielaviopsis vinca root rot

Stunting during growth and yellow leaves are the first signs of this disease. Roots, when you dig them out, are black, and in advanced stages turn to mush. Spore sacs dot the root systems: tiny pinhole-size white sacs.

Treating rotting, wilting Vinca flowers

Infection in a pot or container

It’s rare that such an infection happens in pots, because usually drainage is much better than in the ground. However, if your Vinca presents some of the symptoms, do the following:

  • Stop overwatering, only water when the soil is dry. Do the “scratch test“, where you scratch to 1 inch (2-3 cm) deep to feel if the soil is dry yet or not.
  • Repot your plant with a better-draining soil mix (use sand, gravel, clay pebbles or even pieces of pine bark mulch).
  • As a bottom layer, spread 2 to 3 inches of gravel or clay pebbles.
  • Verify that the hole for excess water to drain out isn’t plugged.
  • As you would to prevent damping off in seedlings, douse the soil mix with a fungus-controlling weed tea or with a couple spoonfuls of grated charcoal.

Sick Vinca in a growing bed

It’s more difficult to correct the issue outdoors in a flower bed. Six techniques will help you deal with root rot even if the original soil and location weren’t ideal.

  • Stop watering regularly. Only perform the “scratch test” described above.
  • If you have a thick layer of mulch, remove it to let soil dry out faster.
  • Increase drainage by aerating the soil: sink a steel bar or tomato stake a foot deep and pull it out. Repeat every 2 inches (5 cm) in all directions.
  • Remove infected plants. Best increase chances for other plants.
  • Get to know the “water needed wilt“, and only water when you notice it: leaves sag down somewhat.
  • As for potted vinca, treat against fungal diseases with fermented weed tea such as horsetail tea or other natural solutions

If you notice the disease in good soil with newly purchased plants, check with the garden store you bought them from. Perhaps the infection originated there, they’ll be grateful for the warning!

How to determine if soil is too wet for Vinca

Soil that will foster fungal disease in Vinca plants will usually be constantly waterlogged. Since Vinca is also a shade plant, sometimes the sun can’t evaporate water fast enough if the soil is clay.

After rains, the soil will stay slimy or soggy for hours. Even the next day, scratching the soil reveals soggy wet material.

Twigs and wood stems are blackish, a sign that anaerobic bacteria are the only ones able to work on decomposing organic material. Soil life is reduced, there aren’t many worms or insects such as thrips to aerate it.

Preventive action keeps root rot out of your vinca bed

It can take years to control a severe fungal infection. To speed things up, you’ll need to greatly enhance the soil.

  • Go for raised gardening. Indeed, a raised bed naturally drains much better. It will invite worms and insects that will make soil structure better. Soil beneath it will gradually turn lighter even as your plants benefit from optimal growing conditions higher up.
  • Make soil lighter.
  • Repopulate soil with healthy fungus, which is what aforementioned fermented weed tea permits.
  • Over consecutive winter seasons, build organic matter into the soil. For example, animal manure, compost, wood chips or green manure will change the game completely after 4 to 6 years.
  • Alternatively, simply select plants that like heavy soil very much!

Read also:

Smart tip about rotting vinca plants

Don’t be afraid to simply throw dead plants to your compost. The fungus that killed them is already present everywhere in your garden. What triggered it was the wrong growing conditions.


Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Vinca plant rotting by Beresa Barnett ☆,
Nature & Garden contributor