herbaceous review

Fast crop bedding plants and cultural practices

• Plug size: fast growing bedding plants (petunias, impatiens) often benefit grom smaller plugs (128-288) as they transplant quickly and finish rapidly. Large plugs may finish too soon or become root bound 

• Temperature: warmer temps (70-75F days, 65-70F nights) accelerate growth, so managing DIF (day night temps difference) is critical. For height control, negative DIP (cooler days than nights) helps reduce stem elongation 

• Fertilization: fast crops need early and balanced feeding. Excess NH4+ promotes soft, stretchy growth, while NO3- encourages hard, compact plants. Use a 13-2-13 formulation early to avoid phosphorus overload 

Four ways to “hold” plugs

1. Temperature reduction: lowering greenhouse slows metabolism (dropping to 55-60F holds growth without damage) 

2. Water stress: slight underwatering slows cell expansion but must be closely monitored to prevent stress 

3. Nutrient limitation: reducing nitrogen and overall EC reduces elongation and soft growth 

4. Chemical PGRs: applying low rate Bonzi or Sumagic can delay further elongation with long lasting effects on plugs

Watering strategy changes

• Just after transplanting: light frequent watering to settle roots and avoid waterlogging 

• Establishing plants: increase water volume with longer intervals to promote deep rooting 

• Finishing the flats: water uniformly to avoid stress but reduce frequency to harden plants before shipping

Seed viability vs vigor

• Viability: ability of seed to germinate and produce a normal seedling 

• Vigor: seeds strength and uniformity under less than ideal conditions

Plug stage 1 vs stage 1 ½

• Stage 1: imbibition and radical emergence. Focus on warm temps and high humidity 

• Stage 1 ½: cotyledon expansion beings, and light becomes essential. Start gentle mist reduction 

• Begonia fertilization: start fertilizing around stage 2 with 25-50 ppm N

  • Why: cotyledons are photosynthetic and root primordia form 

  • Fertilizer concentration: 50-75 ppm N CLF (constant liquid feet)

Ideal fertilizer ratio and N form

• Ratio: 13-2-13 (low phosphorus, moderate N and K) 

• Best N form: Nitrate (NO3-) for compact, sturdy growth

Two technological advances

• Controlled environment propagation: high humidity tents, mist control 

• Improved sanitation and virus free stock: tissue culture, culture indexing

Direct unrooted grower vs rooting station

• Direct unrooted grower: sticks cutting, grows and sells finished plants. Shorter chain, faster turnaround 

• Rooting station: roots cuttings, then ships to finish grower. Specializes in root development and sanitation

Culture indexing vs. virus indexing

• Culture indexing: grow plants in controlled conditions to monitor symptoms 

• Virus indexing: uses serological/molecular tests (ELISA, PCR) to detect specific viruses

Preforma vs ellepots

Feature	preforma	ellepots
rooting	Excellent air pruning	moderate
Handling	Easy to automate	Requires mechanical fillers
Transplant shock	Minimal	Slightly higher
Cost	Higher	More economical

Susceptible species

Zonal geranium (Pelargonium x hortorum) is most susceptible to oedema

Flowering response conditions

• Before flower bud initiation: high light and warm temps are critical 

• Before visible bud: cool temps (50-60F) help limit vegetative stretch and improve flower quality

Sprench vs Spray

Sprench: high volume application (2-4x spray rate), partly drenches media. Used for plugs to ensure uniform, lasting effect

• Why use sprench: better control, longer lasting than foliar spray, less phytotoxic risk 

Better spray instructions

Instead of “spray till runoff” say: apply 0.5 gallons per 100 sq ft using a uniform pressure sprayer, avoid runoff… more consistent and avoids overdosing or uneven coverage

PGR pre germination methods

• Seed coating: a rest included in pelleting for early elongation control 

• media spray: treat plug trays prior to sowing for early stage regulation

PGR classification and identification

Trade Name	Common Name	Notes
1. Flurprimidol	Topflor	✅ ⭘ Triazole
2. A-Rest	Ancymidol	* Triazole-like
3. Pistill / Florel	Ethephon	⭕ Not anti-GA
4. Bonzi	Paclobutrazol	✅ * Triazole ☑ Bark reduces efficacy
5. Sumagic	Uniconazole	✅ * Triazole ⬜ Least active ☐
6. Cycocel	Chlormequat-Cl	✅ ⭕ Non-triazole
7. B-Nine	Daminozide	✅ ⭕ Not triazole

Legend:

• ✅ Anti-gibberellin
  
  

• ⭕ Not anti-GA
  
  

  • Triazole
    
    

• ⬜ Least active (none; Sumagic is most active)
  
  

• ☑ Bark medium affects (Bonzi)

PGR calculations

Given: 

• 3000 sq ft of petunias 

• Sumagic 2 ppm spray 

• Sumagic = 0.055% a.i. =550 ppm per mL 

Spray volume: 

0.5 gal/100 sq ft → 0.5 x 30= 15 gal 

Sumagic needed: 

2 ppm x 15000 mL/ 550= 54.55 mL 

Cost: 

$96.50/946 mL= $0.102 per mL → 0.102 x 54.55= $5.56 total 

3000 sq ft/ 1.69= 1775 flats → %5.56/1775= $0.0031 per flat 

A rest 8 ppm 

0.0264%=264 ppm/mL 

8ppm x 15000mL/254= 454.55 mL A-Rest 

Juvenility vs reproductive vegetativeness

• Juvenility: plant is incapable of flowering, regardless of environment 

• Reproductive vegetativeness: can flower only when mature or after size threshold (40-50 leaves in lavender)

Stratification and fall sowing

• Stratification: cold/ moist storage stimulating winter (usually 40F, 4-6 weeks) 

• Fall sowing: natural winter conditions replace need for artificial stratification

Columbine cold treatment failure 

• Possibly juvenile, or old treatment was too early 

• Cold treatment must follow sufficient vegetative development (6 leaf stage minimum)

Overwintering sketch

• Tender perennials quonset

  • Double poly 

  • Heaters, row covers 

  • Temp >38F 

• Hardy perennial quonset: 

  • Single poly 

  • Passive ventilation 

  • Temp may dip < freezing

Environmental conditions influencing FBI 

• Cold treatment 

• Long day photoperiod

Does overwintering replace cooling

No. cooling requires specific timing and developmental stages for flower induction

Price vs cost objectives

• Identify profit margins: cost analysis reveals which crops are profitable 

• Guide production planning: allocate space and labor toward high margin crops, reduce low yield items

Which of the following inputs is not almost always considered a fixed cost 

• A production labor 

  • Is considered a variable cost because it changes with the number of units produced. For example, the more flats you need to transplant, the more labor hours are required 

  • Depreciation on equipment, management salaries, and repair cost are typically fixed costs because they do not fluctuate significantly with te level of production. These are consistent overhead expenses that recur regardless of how many plants are grown 

What of you want to cut back on labor cost, what aspect of the production cycle would you focus on and why

• Care as needed 

  • Watering is a daily, ongoing activity. It consumes the most consistent labor hours over the duration of a crops life cycle 

Overhead cost calculations example

1000 flats of petunias 

Occupy 1690 ft^2 

Held for 4 weeks 

overhead= $0.20 ft^2/week 

Total overhead: 

1690 ft^2 x 0.20 $/ft^2/week x 4 weeks = $1352 

Overhead cost per flat: 

$1352/ 1000 flats = $1.352 per flat

Variable cost (change with production volume):

1. Pots: more plants = more pots 

2. Rooted cuttings or seeds: directly tied to number of plants produced 

3. Fertilizer: applied as needed based on plant numbers 

4. Plant growth regulators (PGRs)/pesticides: cost scales with treated area 

5. Direct labor (sticking cuttings, transplanting, pinching, watering): labor hours increase with crop volume 

Fixed Costs (remain stable regardless of production volume):

1. Depreciation on equipment: fixed annual expense, whether producing 10 or 10000 flats 

2. Greenhouse structure and maintenance: building cost is incurred regardless of use 

3. Salaries of salaried staff (managers, accountants): paid consistently 

4. Insurance: annual premium unaffected by crop load 

5. Property taxes: statice overhead cost based on land/building value

juvenility

• juvenile stage: plant cannot respond to a flowering stimulus (inductive condition)

• mature stage: plant can respond to a flowering stimulus

• often measured by number of leaves unfolded

• breeders targeting shorter or no juvenile periods in recent years

• when relevant: herbaceous perennials

  • phlox

  • dianthus

  • hosta

photoperiod

• photosynthesis at maximum at 3500 f.c., 14 mol light per day

• supplemental light on cloudy days to keep plugs compact, build density, promote branching

• manipulation of photoperiod for sensitive species can hasten or delay flowering

photoperiod- short day

• facultative: flowers more quickly under SD and with fewer nodes below first flower

  • zinnia hybrida ‘Profusion’

  • celosia plumosa ‘Kimono’

  • cosmos bipinnatus ‘Sensation White’

• obligate: SD required for FBI

  • celosia plumosa ‘Flamingo Feather’

  • cosmos sulphureus

photoperiod- long day

• facultative: flowers more quickly under LD and with fewer nodes below the first flower

  • ageratum houstonianum ‘Blue Danube’

  • calendula officinalis ‘Calypso’

  • dianthis chinesis ‘Ideal Cherry Picotee’

• Obligate: LD required for FBI

  • labelia erinus ‘Crystal Palace’

  • Petunia ‘Wave Purple’

photo-accumulation

day neutral

• FBI unaffected by daylength but light intensity and temperature influence flowering

  • begonia semperflorens

  • impatiens wallerana

  • nicotiana alata

  • tagetes potula

  • zinnia angustifolia

photoperiod x photo accumulation

• facultative irradiance response

  • within each photoperiod group, increased light intensity (up to 14 mol/day) will shorten juvenile phase and delay flowering

    • using HID light from 10pm to 2am to provide LD reduces time to flower over using incandescent lighting to break night length because intensity is higher

• irradiance indifferent response

  • OLDP-II

  • DNP-II

facultative irradiance response

• species exhibiting a facultative irradiance response flower faster because the juvenile stage of development is shortened under high light levels

• so plants form fewer leaves before initiating flowers than those grown under lower light levels

• salvia farinacea has a facultative response

  • usually: plants form 24 leaves before flowering under LD

  • yet form only 18 leaves before flowering wen grown with an additional 150

Hormones

anti gibberellins

• response varies by species/chemical

  • B-Nine to gerbera delays flowering 1 week (usu, PGR applications delay flowering

  • cycocel to seed geraniums induces earlier flowering

  • larger plug cells require less PGR treatments

stress

• FBI faster with some species when water stressed and or nutrient stressed

• death row flowers

FBI

flower bud initiation