Strengthening Peony Stems with Silicon

In addition to flower shape, color and fragrance, mechanical strength of the inflorescence stem is an important factor in determining the quality of a cut flower. While aesthetic attributes seem to drive peony breeding, it seems that selections often result in weak inflorescence stems. Silicon, the second most abundant element in the earth’s crust, is not considered an essential element for plant growth, but has been shown to improve plant environmental stress tolerance and enhance disease resistance. This research evaluated the effects of silicon application on the mechanical strength of the inflorescence stem in Paeonia lactiflora.

Foliar spray treatments of 0, 100, 500, 1000 and 2000 µg/mL sodium silicate were applied once a week from leaf expansion until full bloom stage. Plants were sprayed to the point of runoff. Evaluation measures included using morphological indices, observation under scanning electron microscope, cell wall materials fractionation and lignin content determination, gene expression analysis, and X-ray probe microscopic analysis of silicon content

This research suggests silicon applications could significantly enhance the mechanical strength of inflorescence stems in P. lactiflora by enriching the cortex and xylem. The rate of 500 µg/mL sodium silicate was the most effective treatment concentration.

Zhao, D., Z. Hao, J. Tao, C. Han. 2013. Silicon application enhances the mechanical strength of inflorescence stem in herbaceous peony (Paeonia lactiflora Pall.) Scientia Horticulturae, pp. 165-172.


Evaluation of Postharvest Dry Storage

Dry storage saves room in coolers by allowing more stems to be stored in a small space, but it can be more labor intensive and costly due to packing and recutting after storage. Stems stored in water maintain good turgor and do not need to be packed, but they require more space, the buds may open more quickly and there may be more opportunity for pathogen contamination. Considering there are pros and cons of each method, the greatest determining factor is how species perform in each storage environment. This study evaluated lisianthus, zinnia, rose and marigold in wet and dry storage. 

Cut stems were stored in either a standard cardboard storage box lined with newspaper, or in a bucket with tap water. Both treatments were placed in a cooler at 2C. for 1, 2, or 3 weeks. Following storage, the stems were recut and placed in vases in a postharvest evaluation room. A control treatment consisted of stems placed in tap water in a postharvest evaluation room with no storage. Data collected included vase life, prestorage initial fresh weight, post-storage fresh weight, termination fresh and dry weight, water uptake, final solution pH and EC, initial and final number of buds and flowers (lisianthus only), flower opening at day 7 (roses only), and reason for vase life termination. 

Marigold performed well with dry storage. Roses preformed similarly in dry storage as they did in wet storage. Zinnia and lisianthus performed poorly after dry storage. The species-specific responses highlight the need for further evaluation of the effectiveness of dry storage on additional species and cultivars.

Ahmad, I., J.M. Dole, A. Amjad and S. Ahmad. 2012. Dry Storage Effects on Postharvest Performance of Selected Cut Flowers, HortTechnology, pp. 463-469.


Cork vs. Vermiculite as a Germination Top Coat

Cork oak is a forest tree species whose cork cambium in the outer bark is harvested for cork production. Cork, as such, is considered a natural and renewable raw product. Waste cork, low-quality cork and virgin cork (rough and irregular cork bark coming from the first harvest) are used to produce cork granulates. This research compared cork granulates to the common substrate component vermiculite, specifically for use as a top coating in seed germination.

Using an amended peat substrate in a mini-plug tray, seeds of the following crops were sown: ‘Rutgers Select’ tomato, ‘Dazzler Lilac Splash’ impatiens, ‘Orbit Cardinal Red’ geranium, ‘Better Belle’ pepper, and ‘Cooler Grape’ vinca. The seeds were covered with a 4-mm top coating of either vermiculite or cork granulates. Days to germination, germination percentage per plug tray, dry shoot weight and dry root weight were some of the parameters measured.

Although cork granulates held less water and had a higher air-filled pore space than vermiculite of a similar particle size, no deleterious effects related to germination were observed for the species in this experiment. In fact, in some species a decreased number of days to germination and an increased number of seeds germinating were observed with cork as the top coat.

Bozzolo, A. and M.R. Evans. 2013. Efficacy of Cork Granulates as a Top Coat Substrate Component for Seed Germination as Compared to Vermiculite, HortTechnology, pp.114-118.

Low Temperature Storage and Sucrose Pulsing in Lily

Though chilling injury is rarely found in cut flowers, it has been suggested that lily inflorescences are susceptible to chilling injury manifested by buds not opening. This study examined the difference between dry and wet cold storage with respect to chilling injury and the effect of sucrose pulsing prior to cold storage.

Stems of Lilium ‘Brindisi’ were harvested when the lowermost bud showed some color on the outer tepals. Those stems that received a sucrose pulse treatment were placed in water containing 20 or 100 g/L sucrose and held at room temperature for 20 hours. The pulse treatment group and a non-pulse treatment group were then placed in a cold room (2.5C) for 5, 10, 15 or 20 days. In cold storage, all stems were held upright, in bunches, though half the stems were held in water and half were held dry. A control group was held at room temperature. Observations included: number of buds per inflorescence, time to bud opening, number of desiccated buds, number of malformed flowers, time to tepal senescence and time to tepal abscission.

The cultivar evaluated demonstrated chilling injury when stored at 2.5C in water for 5 days or longer. When stored dry, the injury occurred more quickly. The observations of damage in young floral buds, though not in older, still closed buds, suggests a higher chilling sensitivity in younger tissue. No buds opened during cold storage (even after 20 days), indicating a greater temperature is required for bud opening.

The 100g/L sucrose pulse treatment alleviated some of the signs of chilling injury (slow bud growth, lack of bud opening and bud desiccation) in those stems stored at 2.5C in water.  However, tepal senescence and abscission appeared to be unaffected by the pulse treatment.

Assuming that a vase life of 7 or more days is desired, this study suggests stems harvested in summer and late fall can be stored in water at 2.5C for 5 days, or up to 10 days with a 100g/L sucrose pulse treatment prior to storage. Likewise, stems harvest in summer can be stored dry for 5 days at 2.5C with a prior sucrose pulse treatment for a minimum vase life of 7 days. Summer cut stems stored dry without the sucrose pulse and winter-grown stems stored wet, with or without the sucrose pulse demonstrated a vase life less than 7 days. Winter-grown stems exhibited significant leaf-yellowing in storage.

Prisa, D., G. Burchi, W.G. van Doorn. 2013. Effects of low temperature storage and sucrose pulsing on the vase life of Lilium cv. Brindisi inflorescences, Postharvest Biology and Technology,  pp. 39-46.

Megan Bame

Megan Bame is a freelance writer in Salisbury, North Carolina. Contact her at [email protected]