July 2019 Culture

Culture Report: Primula Paradiso and More By Kathy KcKay

There are several types of primula available in today’s garden centers. Primarily known as a cool season plant, primula is versatile for indoor and outdoor use. With longer shelf life, improved uniformity and a whole range of colors, it is a wonderful addition to any program.

Schoneveld Breeding is focused on developing and producing quality primula seeds of acaulis, polyanthus and obconica types. Features such as genetically superior plant structure, uniformity, aesthetically appealing blooms and colors as well as sustainability are key components.

Here are the main attributes of each type of primula to decide which series is best for you.

PRIMULA ACAULIS

Paradiso is a series which is environmentally friendly to cultivate. With this series, the amount of growth regulators is reduced. Less growth regulator is better for the environment and saves money. Furthermore, the grower has greater control of the crop.

Paradiso is available in four types:
Paradiso Early: Suitable for early season. Requires little to no cool treatment.
Paradiso Mini: Compact growing Primula acaulis. Great for 3-inch pots.
Paradiso Mid: Can be grown with less growth regulator and is less susceptible to leaf yellowing. Suitable for early to midseason shipping. Requires minimal cooling.
Paradiso Late: These varieties have a good shelf life and uniform blooms. Great for late and extended season programs for spring. This series does require cool treatment to flower.

PRIMULA OBCONICA

Touch Me (Primin Free) is a true spring plant with beautiful, firm, bright green leaves and cheerful flowers. It comes in both soft tints and truly vibrant colors and provides a really glorious touch of spring. Together with the new flowers, which are lighter in color, this creates a very special effect. Touch Me is ideal for use in 3-inch, 6-inch and gallon pots.

Touch Me Mini: Genetically small compact plant, suitable for 3- to 4-inch pot sizes.
Touch Me Midi: Firm flower stems, bright colors and a long flower life.
Touch Me Large: A strong plant with a genetically compact structure.
Pricanto: Pricanto has magnificent vintage colored flowers with a nostalgic edge.
Original: this is the only Primula obconica from Schoneveld that does contain Primin, giving the plant natural resistance to insects.

PRIMULA POLYANTHUS

Perola is a long-stemmed primula that is characterized by its
exceptionally strong stems, which prolong the flower life. It has a longer shelf life than the standard Primula acaulis. It has a more open structure and higher production of flower stems (compared to acaulis) making Perola less sensitive to Botrytis.

ACAULIS GROWING RECOMMENDATIONS

Germination. Sow seeds in plug trays filled with a fine textured peat mix with an EC between 0.7 and 0.9. It is not necessary to cover with vermiculite unless maintaining moisture is a concern. During germination, maintain moderate moisture levels, being careful to not allow seeds to dry out or become saturated.

Temperatures of 59 to 64° F are suggested during germination to improve uniformity. Starting in a germination chamber can be useful during this period and increase germination rate. Seeds should germinate in seven to 10 days. Once germinated, temperatures can be increased to 61 to 65° F and soil moisture can dry slightly between watering.

Once true leaves are present, fertilization can be applied at 75-to 100-ppm nitrogen every third watering or 50 ppm of a well-balanced water-soluble each watering is recommended. The pH should be maintained at 5.5-6.2.

Primula are sensitive to high light levels. To prevent burning, provide 30 to 50% shade when natural light levels exceed 3,000 foot-candles.

The plants are ready for transplant when they have at least four developed leaves. Plugs should be ready to transplant approximately six to seven weeks after sowing.

Transplant. Fill the pots to the rim with well-aerated potting compost enriched with lime and fertilizer, pH 5.8 to 6.0 and EC 0.8 to 1.0. Make sure the plugs are sufficiently moist and planted even with the medium. Planting too deep can result in crown rot.

Climate. During the first 10 weeks, maintain the temperature at 50 to 57° F. Then gradually lower the temperature to no less than 37° F. The plants need a cool temperature for proper finishing. This is especially relevant for the late series of Paradiso.

It is suggested to maintain your relative humidity at 60 to 80%. In all circumstances, ensure there is an active climate via ventilation by using fans or setting the heating pipe to a minimum temperature.

The first two to three weeks after transplant, set the light levels to 450 to 500 W/m². As soon as the roots are visible at the edge of the pot, gradually increase the light levels to 500 to 650 W/m². You may need to use a movable screen, net or chalk the greenhouse roof depending on your conditions.

Watering. After transplant, water the plants from above for the first few weeks (moisture level 3 to 4) to encourage good growth and a good microclimate. It is a good idea to water in the mornings so that the crop is dry before nightfall. As soon as the first roots are visible at the edge of the pot, the plants can be grown under drier conditions (moisture level 3). When first buds are visible, it is preferable to water from below.

Fertilization. During the first six to eight weeks use an NPK fertilizer including trace elements with an N:K ratio of 1:2. Add calcium and iron (EDDHA) to the fertilizer regularly. Depending on the growth, adjust the N:K ratio to 1:3 or 1:4. Aim for an EC of 0.5 to 0.7 in the pot. Also, monitor your nutritional status in the pot by taking soil samples once every four to six weeks.

Growth regulation. Growth can be regulated by timely fertilization with additional potassium. As well, keeping the plants a little dryer or applying a temperature drop are a couple other methods of maintaining plant size. If necessary, chemical growth regulators Dazide and Propiconazole may be used.

CROP PROTECTION

Here are a few pests and diseases that may damage your Primula acaulis crop. Apply preventive measures regularly.
• Botrytis
• Bacteria Pseudomonas or Acidovorax
• Ramularia primulae (leaf spot disease)
• Thielaviopsosbasicola
• Mycocentrospora
• Whitefly
• Leaf miner
• Caterpillars
• Fungus gnats (Sciara)
• Thrips
• Mites

Note: All information provided in these growing recommendations has been carefully compiled from our own observations and internal trials in Northern Europe.

For culture information for the Primula polyanthus, Primula obconica or other Schoneveld genetics, please contact Kathy McKay.