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Series: Primera™, Orion®


1. Soil and pH Needs

Primulas are tolerant of a wide range of soil conditions, but prefer a rich soil with good drainage. 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 Canadian sphagnum peat moss and well-rotted compost are good sources of organic matter that will aid in aeration. If possible, incorporate two to three inches of organic matter into the top six inches of soil. 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- 6.0 for optimum growth; 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. 


2. Fertility

Primulas are light feeders; providing moderate to high fertility levels (particularly from ammonium sources) causes them to appear lush and leafy, and will limit flower production.  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 applied and the average daily temperature. In high pH soils (alkaline soils) additional iron or iron sulfate may be beneficial to reduce chlorosis (yellowing) of the foliage.  Yellow foliage on Primula may also be caused by a nitrogen deficiency within the plant. Both can be corrected with the proper supplemental fertilizers. 


3. Disease

The primary diseases you should watch for are Botrytis, powdery mildew and Ramularia leaf spot. Botrytis can be identified on the foliage; especially those near the soil surface will rot and become covered with gray fungal growth.  A plant with powdery mildew will have white fungal growth on the upper leaf surface; it may also form on the flower petals. Ramularia leaf spot will begin as yellow spots on the foliage later turning brown. These diseases can be avoided by employing proper cultural practices such as: avoiding overhead irrigation, improper plant spacing, poor air circulation, and watering too late in the day.


Botrytis infection at the soil surface


Symptoms of powdery mildew


Ramularia in a Primula crop


4. Insects

Occasionally, aphids, slugs, spider mites, and thrips may appear and cause a minimal amount of crop injury. Aphids are tiny soft bodied insects that cluster on the growing tips of leaves and flower stems, sucking plant juices. The plants become stunted and deformed. Spider Mites are tiny pests that also feed on plant juices. Primula leaves will turn yellow and eventually drop off. Slugs are worm-like pests that feed on plant leaves and stems, often at night. Thrips cause damage to the plant by piercing and sucking cells on the leaf surface. This causes silver-grey spots to form on the foliage. At high infection rates, the leaves may wither. Remember that healthy, vigorous plants are less susceptible to pest damage than unhealthy plants.  


Leaf showing signs of a spider mite infestation


Slug infestation


Petal blotching caused by thrips


5. Tips for Success

  • Primulas grow best in moist, slightly acidic soil and light shade.
  • When irrigation is necessary, water thoroughly then allow the soil to dry slightly between watering.
  • Deadheading (removal of spent flowers) will prolong bloom time and help produce a fuller plant.
  • Primulas do not tolerate very hot or humid weather. 
  • Remove weeds from the plantings that compete with Primula for moisture, nutrients and light.

Information provided by Syngenta Flowers