Hybrid Phlox: Have a Sunny Future By Rick Schoellhorn

The hybrid phlox market continues to expand, and that is a very good thing. We have existed as an industry on the old standards for so long that this genus is overdue for revitalization. In the past, most of the development was with hybrids of annual phlox (Phlox drummondii). In the last few years, however, breeders have started crossing this colorful spring annual with species that have increased heat tolerance, reduced sensitivity to powdery mildew and an extended blooming season. The result is that a whole new line of vegetative annual phlox has entered the market. While they are still annuals, these plants represent a breakthrough in breeding with huge benefits for growers and consumers.

Series Characteristics

It all began at the 2003 Pack Trials with the release of the Intensia phlox series from Proven Winners. Suntory released the Astoria phlox series at the 2004 Pack Trials, and this year Westhoff released the PowerPhlox series. All the genetics are very similar, but if you are a breeder, you know that the parent stock and the selection process is different for each. Both Astoria and Intensia were bred in Japan and are very similar in their genetics. In the selection process, however, Proven Winners selected for larger landscape plants, and Suntory appears to have worked for a more compact plant. To my knowledge, the Westhoff series has not been trialed yet. We will know more about how this series performs after the university trials are completed this summer, but it appears to be more compact than Astoria.

You can’t talk phlox without discussing the 21st Century series from PanAmerican Seed. This is arguably one of the top seed-produced phlox varieties on the market. The main difference between 21st Century and the vegetative types is that 21st Century does not have the influx of heat-tolerant genes like the other series. It will do extremely well in most situations but, like all seed phlox, produces seed. When plants make seed, they are diverting energy away from additional flowers. The peak season for this crop is slightly more concentrated than the newer hybrids. For growers, this is a great crop, and seed is almost always less expensive than vegetative cuttings. It comes down to making a choice about what you want to grow, and I highly recommend trialing all these varieties at your operation to see for yourself what works best for your nursery.

Understanding Production

Intensia and Astoria production is basically the same, and until we know differently about Power-Phlox, you should apply the same guidelines to it. The key to success is to time your orders correctly and follow some simple guidelines upon rooting and transplanting. The main problem most growers have with this crop is they try to get started too early, and the combination of cold temperatures, low light levels, cold soil and overwatering leads to problems in producing strong 4-inch plants.

There are three important culture requirements for hybrid phlox. As with all phlox, one of the crucial keys to success is high light levels: Without this, you are fighting an uphill battle all the way. Secondly, because these hybrids include phlox species with more heat performance, they also prefer a warmer production environment. So you want to keep the plants warm to encourage vigorous growth. Lastly, part of the beauty of these hybrids is that they have quite a bit of drought tolerance and prefer well-drained soils, which means growers need to watch their watering and avoid prolonged wet conditions. This has two benefits: The plants do better, and lower water levels mean less stretch, so it is easier to produce higher quality plants.

When I was trialing for the University of Florida, the Intensia series was probably the highest-rated plant in our trials for three years running. Another thing we learned is that hybrid phlox can be a great winter plant for the Deep South. Although they prefer a warm production environment, under temperate winter conditions (with high light levels) they are outstanding winter color, blooming through the Southern (no freeze) winter and holding flowers in field trials down to the 20 degree F range. So for milder winter areas, don’t limit yourself on the season you use these plants. The key here is high light!

What’s Next?

What is in the future for annual phlox? I think there will be an increasing number of new hybrids with differing levels of perennial performance, fragrance, habits and colors. Even with all the improvements we have seen so far, there is still a lot of room to grow this group of plants into a larger market.

The improvements don’t stop with Phlox drummondii and its hybrids. We are beginning to see the emergence of a new group of Phlox paniculata cultivars as well, and I think this is just the tip of the iceberg. The goal here is to take this traditional perennial crop and overcome its natural flowering cycle so it can be produced on a more year-round basis. Hybridizing with other species offers a lot of potential, and it will be interesting to see what the future brings. Though neither series is new, I think the Flame series from Ball FloraPlant and the Volcano series from Anthony Tesselaar are both good indications of where this crop may be moving.

Currently, we have phlox species that survive from Anchorage to Miami, and that is a very good thing if you are a breeder as it means there is a lot of variability out there that can be used to reshape this plant for new gardeners. The advances in molecular genetics and tissue culture as well as embryo-rescue techniques are opening doors to new concepts in plant hybridizing.

I think the future is very bright, not just for phlox, but for many species. Color, texture, performance, disease tolerance – all of these factors can be improved through good breeding. It is great to see good plant breeding at work in all the plants discussed here, and though it frustrates plant breeders to no end, the question is always the same: “That’s beautifulÉWhat’s next?”

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Rick Schoellhorn

Rick Schoellhorn is director of new products for Proven Winners LLC; he can be reached at [email protected]

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