March 2009

Zinnia Distance Series By Jason Riley

Zinnias are as Americana as hot dogs on the Fourth of July, county fairs, night baseball games and apple pie. Memories of grandmothers tending to their rows of zinnias are as ubiquitous as the ants at those very same Fourth of July picnics. This is probably why zinnias remain an anchor of so many spring and summer production schedules. It also doesn't hurt that they're quite rewarding for the home gardener yielding myriad ruffled flowers ripe for cutting and gracing a summertime dinner table.

Variety Information

Growers are happy to accommodate this demand for zinnias given their relatively cheap cost when compared to vegetative items. Helping to fulfill this demand for high-quality zinnia elegance are the Distance zinnias from Bodger Seeds, Ltd., introduced two years ago. Each of the seven colors are suited for displacing the more expensive 4-inch or gallon container, vegetative, summer offerings. Reaching 12-16 inches high, they are a solid choice for each of these containers, especially if light PGR applications are used. In these containers, Distance zinnias, with their many, large flowers, superior branching and reserved habit, are a great alternative to vegetative items.

Offered in White, Yellow, Scarlet, Cherry, Pink, Grape, Orange and a full mix, Distance zinnias will provide full to semi-double flowers up to 31/2 inches across. While many other zinnias may have similar-sized flowers, Distance varieties provide more of them at any given time, due to their branching characteristic. This quality is directly attributable to the use of well-branching lines in the breeding of Distance zinnias. For many years, Dasher zinnias, also bred and offered by Bodger Seeds, was a stalwart in the zinnia market. They basally branched very freely and held many flowers at a time. For this reason, the Dashers were chosen to be an integral part of the Distance's bloodlines.

Plug Culture

Plug trays may be finished in three to four weeks. Throughout plug production, a watchful eye on media moisture and EC levels is critical for success. Zinnias are especially susceptible to fungal pathogens, so water management is key. Further, zinnias are very sensitive to elevated EC levels.

For stage 1, maintain media temperature at 72- 75¡ F for best germination. Maintain a just moist but not wet media. Covering seed lightly with vermiculite will help keep high humidity around the seed while minimizing irrigation frequency. Do not fertilize during stage 1.

At stage 2, allow media to dry down further by reducing irrigation frequency. Very low levels of fertilizer (less than 40 ppm) may be applied at this time with a calcium-based formulation. Keep EC levels no higher than .5. Reduce media temperature to 68-72¡ F. At this stage, light levels of 2,000-2,500 foot-candles are acceptable.

Increase light levels to 3,000 foot-candles at stage 3, and maintain dry media conditions. Again with a calcium-based formulation, light applications (30-50 ppm) of fertilizer may be applied. Media temperatures may be reduced further to 65¡ F. EC levels should still remain no higher than .5. For disease suppression, ensure good air circulation around plug trays.

For stage 4, media moisture levels should still remain dry. Light levels can be increased to 4,000 foot-candles. As always, fertilize with a calcium-based formulation at 30-50 ppm. At this stage, PGRs may be applied at light rates. Zinnias respond well to B-Nine (daminozide) at 2,000-2,500 ppm.

Finishing

Zinnia plugs should be transplanted as soon as they are ready. Holding in plug trays too long may result in stunted, prematurely budded plants. Further, the plants may exhibit excessive apical dominance and reduced branching. Transplant into media with a pH of 5.5-6.0. Avoiding regular use of ammonium-based formulations, fertilize relatively lightly with 100- to 150-ppm nitrogen. Always irrigate zinnias early in the day giving the foliage plenty of time to dry before nightfall. Night temperatures should not be allowed to drop below 60¡ F as zinnias do not respond well to cool temperatures. Further, lower temperatures will increase the likelihood of fungal disease. Day temperatures should be in the 68-80¡ F range. Maintain high light levels and plenty of air circulation.

So that Distance zinnias can basally branch as freely as they enjoy, be sure to space plants as soon as they are ready. Growers will be rewarded with well-branched plants with many flowers. Distance respond well to all PGRs. B-Nine at label rates is usually sufficient but if more control is required, Bonzi (paclobutrazol) is effective. If grown under high light and good spacing, one application of B-Nine or Bonzi should be effective enough for desirable results.

Pests and Diseases

Zinnias are susceptible to foliar pathogens including powdery mildew, Alternaria leaf spot, Botrytis and sometimes bacterial leaf spot. Always irrigate early in the day and maintain good air circulation around plants. Scout for aphids, thrip and whitefly.