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Grower 101:

Bulb SoakBasics

Bulb crops are animportant segment inthe yearly rotation fora greenhouse. Theyhelp fill the gap

between the poinsettia and bed-ding plant seasons. The short crop-ping time and limited amount ofbench space required for a largeamount of pots add to the advan-tages of producing flowering bulbs.

A concern many of the bulb cropsis stem stretch during postharvest.Although this does not directly affect

us as growers, it does have a majorimpact on the quality of the pot whenit is in the hands of the consumer.

Recommendations have beenmade for the application of foliarsprays, substrate drenches and pre-plant bulb soaks using various PGRsfor height control. Foliar sprays areeasy to apply, but with the smallamount of leaf area present at appli-cation it is often ineffective.Substrate drenches can be effectivefor postharvest height control, butthe amount of labor required for ➧

Sumagic preplant bulb soaks on ‘Star Gazer’ lilies. From left to right: 0, 5 and 10 ppm Sumagic.

companion coveragePGR Bulb Dips . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page 54

Flurprimidol Ancymidol Paclobutrazol Uniconazole (Topflor) (A-Rest) (Bonzi, Piccolo, Paczol) (Sumagic)

Tulip 10-251 mg per liter n/a 50 mg per liter for 10 minutes 10 mg per liter for 10 minutesfor 10 minutes

Caladium NR @1.25-40 mg per liter n/a NR @ 2.5-40 mg per liter SR @ 1-10 mg per liter for 10 minutes for 10 minutes for 1-5 minutes

Hyacinth 10-251 mg per liter n/a 100 mg per liter for 10 minutes 20-401 mg per liter for 2-10 minutes for 10 minutes

‘Tete a Tete’ narcissus 30 mg per liter for 10 minutes n/a 400 mg per liter for 10 minutes NR @ 5-10 mg per liter for 10 minutes

‘Dutch Master’ narcissus 20 mg per liter for 10 minutes n/a 200-400 mg per liter NR @ 5-10 mg per liter for 10 minutes for 10 minutes

Oriental lily 25 mg per liter for 10 minutes 4 mg per liter for 100-200 mg per liter 5 mg per liter for 10 minutes30 minutes for 5 minutes

Some of these recommendations are based on previously published trials or on the product label.

NR=No response at the rates trailedSR=Suggested rate to begin experiments; label lists no specific recommendation1Concentration depends on cultivar response

Figure 1. Suggested Preplant bulb soak rates.

Soaking bulbs in PGRs before plantingcan be an effective means of heightcontrol for spring bulb crops.

By Brian Krug, Brian Whipker and Ingram McCall

According to the National Gardening Association, in 2002 29 percent(31 million) of all U.S. households grew flower bulbs, and overallflower bulb sales were estimated at $1.2 billion. Whether sales are frombulbs, cut flowers or potted bulbs, this sector is sticking around.William Miller at Cornell University, Ithaca, N.Y., is constantly per-forming research on bulbs, and he recently found some interestingresults when testing the efficacy of bulb dips. We thought it would beuseful to pair this research with some bulb soak basics from researchersat North Carolina State University, Raleigh, N.C. So, keep reading thenext 17 pages for the most up-to-date research on PGRs and bulbs.

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application may be prohibitive.Preplant bulb soaks have shownpromise for an effective, easy-to-apply PGR treatment, but informa-tion about application concentra-tions and protocols is limited andsometimes vague.

At North Carolina StateUniversity, Raleigh, N.C., we havebeen trialing preplant bulb soaksto better understand how to usethe different PGRs on a wide vari-ety of bulb crops. The followingwill answer some common ques-tions about how to apply preplantbulb soaks based on this research.

Bulb Soak Q&AQuestion: How long before pot-

ting can I soak the bulbs?Answer: In our trials, we soaked

hyacinth bulbs the day of, the daybefore and seven days before planti-ng. After soaking we returned thebulbs to proper storage conditionsuntil we potted. We found no differ-ences in the amount of height controlprovided by any of the treatments. So

the procedure allows some flexibilityas to when you can soak the bulbs.

Question: How many bulbs can Isoak in a given amount of solution?

Answer: We soaked 100 hyacinthbulbs, five at a time, in 1 liter ofsolution. When we finished soakingthe last set of five bulbs there wasnot enough solution to soak anoth-er batch, but we found no differ-ence in the height control from thefirst to the last batch. On average,each bulb utilized 4-8 ml of solu-tion, meaning it would takeapproximately 370 bulbs to use up1 gal. of solution; however, 370bulbs will not fit in 1 gal. of solutionat the same time. Based on ourresults, the solution will be used upbefore any loss of efficacy. Researchconducted with hybrid lilies andpaclobutrazol at Cornell University,Ithaca, N.Y., found similar results.

Question: How long do I needto soak the bulbs?

Answer: Many of the product ➧

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Top: ‘Pink Pearl’ hyacinth bulbs soaked in 20 ppm in consecutive batches. From left to right:untreated control, 1st batch, 10th batch and 20th batch. Bottom: Topflor preplant bulb soaks on‘Prominence’ tulips. From left to right: 0, 10, 15 and 20 ppm Topflor.

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labels and other recommendationssuggest up to a 1-hour soak. Most ofour experiments were for 10 min-utes. We also tested bulb soaklengths of 1, 5, 10, 20 and 40 min-utes on hyacinth. After two minutesplant height was the same. We rec-ommend soaking for at least twominutes, but don’t worry if a cus-tomer calls and you have to walkaway for few minutes while thebulbs soak. Other bulbs may vary.Freesias generally require a longertime (60 minutes) because of theoutside tunic. We had excellentresults with 10-minute soaks ontulips, narcissus, dahlias, ‘StarGazer’ lilies and Easter lilies.

Question: How can I dispose ofunused solution?

Answer: You cannot simply pourleftover pesticides and PGRs downthe drain; it is illegal and too expen-

sive to waste. This may not be anissue if you accurately calculatehow much total solution you willneed (approximately 370 hyacinthbulbs per 1 gal. of solution). If youdo have solution left over you canapply it as a substrate drench toanother crop. We applied leftoversoak solution to ‘Pacino’ pot sun-flowers and saw no difference incontrol as compared to freshly pre-pared substrate drench solution.

Question: Does efficacy varywith cultivar?

Answer: Yes, and no…let yourexperience be your guide. We’vegiven a range of recommendationsfor a number of species (see Figure 1,page 44). To determine which end ofthe range to use for a particular culti-var consider its vigor. Notoriouslytall cultivars will need concentrationson the high end of the range, while

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Preplant Bulb Soak ProcedureStep 1. Unpack and inspect bulbs, and store them in a cool, dry locationuntil treatment. Remove packing material (peat, sawdust, etc.) from bulbsprior to treatment with a PGR preplant bulb soak.

Step 2. Mix the appropriate amount and concentration of solution, seeFigure 1, page 44, for suggested concentrations. As always, wear appro-priate protective clothing.

Step 3. Soak batches of bulbs in small quantities to ensure all bulbs aresufficiently submerged in the solution. Quantities should be relative to theamount of solution mixed.

Step 4. Lift the bulbs from the solution, and allow the solution to drainback into the container.

Step 5. Wait at least one hour prior to potting the bulbs.

Step 6. Pot as usual, making sure your potting media is pre-moistened toprevent the need to heavily water in the pots, which can wash the PGRsolution off the bulbs.

Step 7. Continue normal forcing schedule for the crop.

Topflor preplant bulb soaks on ‘Tete a tete’ narcissus. On the left, untreated control, on the right 25ppm (10 days after anthesis).

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the less vigorous cultivars can use thelower concentrations. Conduct a fewtrials of your own to determine whatconcentrations work best for you andyour production system.

Question: Does it matter whatthe temperature of the solution is?

Answer: In our experiments wefound that extremely cold (46º F)or extremely warm (89º F) waterreduced the efficacy of paclobutra-zol and flurprimidol on hyacinthbulbs. With temperatures between60 and 75º F we found consistent,acceptable height control.

Question: Do preplant soaksdelay plant emergence or floweringdate, or limit root development?

Answer: When we saw anydelay, it generally was less thantwo days when optimal concentra-tions were used. The plantsbloomed and grew normally. Anexception was dahlias — the soaksdelayed flowering by one week.

We have found that preplantbulb soaks have been an effectiveaddition to the PGR toolbox for con-trolling the height of a number ofbulb crops. Using these guidelines,you can begin to use preplant bulbsoaks with confidence in your ownproduction system. As with anynew procedure, we recommend test-ing preplant bulb soaks on a smallquantity of pots before you treatyour entire crop. There is a limitedamount of greenhouse height con-

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trol of hyacinth, tulips and narcissus.You will need to conduct posthar-vest trials to evaluate the efficacy onthese crops. Differences in ‘StarGazers’ height were easy to evaluatein the greenhouse. GPN

Brian Krug is a graduate researchassistant, Brian Whipker is associateprofessor and Ingram McCall isresearch technician at North CarolinaState University. Krug can bereached at bakrug@unity.ncsu.edu

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LearnMoreFor more information related to this article, go towww.gpnmag.com/lm.cfm/gp100503

For more information on thePGRs mentioned in this article,direct your questions or concernsto the following manufacturers:

Chemtura Corporation (Paczol)(203) 573-2000www.chemtura.com

Fine Americas, Inc. (Piccolo) (888) 474-3463 www.fine-agrochemicals.com

SePRO Corp. (A-Rest, Topflor)(800) 419-7779www.sepro.com

Syngenta Professional Products (Bonzi)(866) SYNGENTAwww.syngentaprofessionalproducts.com

Valent USA Corp (Sumagic)(800) 898-2536www.valent.com

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