Upright/ Mounded Series: Cora®, SunStorm®, SunDress™, SunGlow™
Trailing Series: Cora® Cascade, Sun Shower™
1. Soil and pH Needs
Vinca needs a soil that drains well, but not one that is particularly rich or fertile. Flowering will suffer if soils are too fertile. However, Vinca does not perform well in wet, poorly drained soils or in cool spring weather. Heavy clay soils will retard root growth and starve the plant of oxygen, which can lead to root diseases. Soil should be amended with fully composted organic matter prior to planting and in the case of clay soils the addition of pea gravel equal to at least 25% of the soil volume will aid in aeration. If adding organic matter, be aware that organic matter that has not been fully composted will tie up nitrogen and sulfur leading to nutrient deficiencies and poor growth. Soil pH should be between 5.5 - 6.2 for optimum uptake of iron and suppression of Thielaviopsis; and should be tested prior to planting but after adding any amendments. This can be done quite easily with a portable pH tester available for about $100. Mix one part soil with two parts distilled water, stir well and wait thirty minutes, then follow the instructions for using the pH meter. If pH is too low, the addition of lime is warranted. However, the rate will vary depending on how much you need to raise the pH and the type of soil you are dealing with. Clay soils or those with a lot of organic material have a high buffer capacity and require more lime than sandy soils, which have a low buffering capacity. A good soil testing lab can determine the lime requirement index (LRI) of your particular soil and can recommend types and rates of lime to use. The frequency of watering will depend on the type of soil, weather conditions and the amount of mulch. Mulch will not only reduce soil water evaporation but will also reduce splashing of water onto the lower leaves, moderate soil temperatures and reduce weed competition. Because they're quite drought-tolerant, vinca seldom need daily watering other than what they receive with rain; in prolonged periods of drought, however, watch that the soil doesn't get too dry.
Vinca are low to moderate feeders in the landscape; and can have a crop life of four – six months. An application of a balanced controlled-release fertilizer (CRF) such as 10-10-10 or 14-14-14 with a 3-4 month formulation applied to the bed at planting will keep the plants well fed, depending on the amount of irrigation required and the average daily temperature. In areas of high irrigation and high temperatures it may be better to use a formulation with a slower release rate since higher temperatures will cause the fertilizer to be released quickly. Fertilizers that are not CRF are not recommended since the fertilizer will be leached out of the root zone long before the crop needs the nutrients. In high pH soils (alkaline soils) additional iron or iron sulfate may be beneficial to reduce chlorosis (yellowing) of the foliage. Yellow foliage on vinca may also be caused by a nitrogen deficiency within the plant. Both can be corrected with the proper supplemental fertilizers.
Water correctly to prevent most of the fungal diseases that can cause problems for vinca such as: root rot, botrytis, alternaria leaf spot, and aerial phytophthora. Of these, aerial phytophthora is the most prevalent; where overhead watering splashes soil and fungus spores onto lower foliage and stems. Lesions develop on leaves and stems, killing the shoot but leaving a healthy root system. The best preventative is to use drip irrigation. At the very least, direct water from the hose onto the soil or mulch, and not on the plants themselves.
In the last 5 years, the Cora® series was introduced and was bred to be resistant to aerial phytophthora. This series performs extremely well in areas with high humidity and temperatures showing no signs of the disease.
Pests seldom bother vinca, you may occasionally find aphids and thrips on the plants. Slugs and snails occasionally feed on the leaves. Larger pests such as rabbits and deer avoid eating vinca. Remember that healthy, vigorous plants are less susceptible to pest damage than unhealthy plants.
5. Tips for Success
- Vinca possesses excellent heat and drought tolerance, blooming continuously through the intense heat of mid-summer.
- Cool temperatures, high fertilization, and overwatering are the most common problems in the landscape.
- Remove weeds from the plantings that compete with the vinca for moisture, nutrients and light.
Information provided by Syngenta Flowers