Starting and growing transplants under lights
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Starting and growing transplants under lights Curtis Swift, Ph.D. Colorado State University Extension What it is? Definition – transplanting is the shifting of plants from one place or growing medium to another Goal is to produce vigorous plants ready to be planted in the garden

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Starting and growing transplants under lights l.jpg

Starting and growing transplants under lights

Curtis Swift, Ph.D.

Colorado State University Extension

What it is l.jpg
What it is?

  • Definition – transplanting is the shifting of plants from one place or growing medium to another

  • Goal is to produce vigorous plants ready to be planted in the garden

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Why use transplants

  • Avoid problems of seed emerging through soil crusts of clay soils

  • You can more closely control depth of planting

  • Seeds germinate under ideal conditions

  • Extends the growing season

  • Earlier harvest is more attainable by using transplants than by direct seeding in the field

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Not All Vegetables Transplant Well

  • Plants difficult or not to transplant include:

    • Root crops (carrots, beets)

    • Leafy biennial herbs (dill)

    • Heading types of Chinese cabbage

    • Cucurbits (cucumbers, pumpkins, squash)

      • Do not like their root systems disturbed

    • Vegetables growing quickly when seeded in the garden (radish, leaf lettuce, spinach)

      • Transplanting is not worth the effort

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Vegetables Traditionally Transplanted

  • Small seed vegetables

    • Tomatoes, peppers, head lettuce, broccoli

  • Some vegetables are traditionally started from transplants because they do not produce seed or the seed lacks vigor

    • Sweet potato, Irish potato

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Commercially Grown Transplants


  • They are easy

  • Inexpensive if you only need a few plants

  • They do not require that you commit time and money

  • Better (ideal?) growing conditions and care

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Commercially Grown Transplants


  • It can be difficult to find “good quality transplants”

  • You may not be able to find transplants of a specific cultivar

  • The transplants may introduce diseases, insects, and weeds into your garden

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Age affects production

  • Smaller, stocky plants that have not started to bloom and/or set fruit will adapt to the garden more easily than leggy transplants that already have small fruits hanging on them.

  • Tomato plants 4-5 weeks old grow and yield better than older transplants.

Best Size – 6 “ tall and 6” wide

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Producing Your Own Transplants

  • Advantages

    • Can ensure disease-free transplants

    • Transplants available when needed

    • Best use of expensive seed

    • Produces transplants you desire

    • Gives you a good feeling

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Producing your own Transplants

  • Problems

    • Low light, excessive nitrogen, and high temperature cause excessive stem elongation

    • Damping off disease

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Producing Your Own Transplants

  • Important factors determining your success

    • Growing media

    • Environmental conditions

      • Light

      • Temperature

      • Moisture

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Producing Your Own Transplants

Growing Media

  • Want to use a soil-less growing media that does not contain soil from your garden or yard

  • Why not use garden soil?

    • Tends to be poorly drained and subject to water logging

    • Contains insect pests, diseases, and weed seed

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Producing Your Own Transplants

Growing Media

  • Characteristics of a good soil-less growing media

    • Free of pests

    • Good water-holding capacity

    • Well aerated and drained

    • Low in soluble salts

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Producing Your Own Transplants

Growing Media

  • Common components of a soil-less growing media

    • Peat moss

      • Provides the base for most soil-less media

      • Decayed remains of sphagnum moss

    • Vermiculite

      • Mica-like material that has been heated to a high temperatures

      • Provides pore space and retains moisture and nutrients

    • Perlite

      • An inert light weight volcanic material

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  • Plant seeds at a depth of 3 times their diameter

  • Broadcast very small seeds such as broccoli or lettuce and cover with a light sifting of soil

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Producing Your Own Transplants


  • Factor most likely to be limiting for good quality transplants

  • Interrelated with temperature and moisture

    • Inadequate light often leads to cold temperatures and too much growth

  • Too little light causes weak spindly plants susceptible to falling over

  • Vegetable transplants need more light than standard houseplants

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  • Plants grown in the dark are yellow (chlorotic), taller (etiolated), have thinner stems, and in general, are not so healthy

  • ultra-violet (below 400 nm)

  • visible (approximately 400-700 nm)

  • far-red (approximately 700-800 nm).

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Producing Your Own Transplants


  • exposure to red light increases seed germination, reduces seedling stem elongation, and promotes lateral shoot growth of many species

  • an increase in red light and/or a reduction in far-red light in the greenhouse can be used to reduce plant height.

  • Plastic sheeting that reduces far-red light is available and have been used to produce healthier plants.

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Fluorescent Lights

  • on for 12 to 16 hours per day

  • no more than 4 inches above the tops of the seedlings

  • One cool-white plus one warm-white tube

    • Or

  • Use Full Spectrum Grow Lights

high in red light relative to far-red light, produces short & compact plants.

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  • High Pressure Sodium

  • ~$90

  • Expensive

  • Very effective

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Incandescent Lights

  • On for 12 – 16 hours per day

  • 1 to 3 feet from top of plants

  • Spot Grow ~$30

    • Has proper plant growth enhancing light

    • Limited space receives light

  • Regular Incandescent bulb

    • Due to high level far-red light relative to red light, frequently lead to stem elongation.

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Red vs. Far Red Light

  • Controlling the red to far red light ratio is a means of controlling seedling height without reducing fruit yield or quality

  • Incandescent lamps, which are low in R:FR ratio, frequently lead to stem elongation while fluorescent sources, which are high in R:FR ratio, produce short and compact plants.

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Producing Your Own Transplants


  • In windows there can often be large temperature fluctuations between day and night or sunny and cloudy days

  • Cooler than optimum temperatures may:

    • Increase disease

    • Cause rough fruit in tomatoes

    • Cause bolting in onions

  • Warmer than optimum temperature may cause weak spindly seedlings

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Root Zone Heating

  • Root zone heating is another method to stimulate quick germination

  • Use a heating pad

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Tomato and PepperAir Temperature

  • Start seeds at 65 - 75 degrees F.After emergence, lower temperature to 60 - 65 degrees F.

    • Day temperature can be about 10 degrees warmer than night temperature.

    • Do not allow to get too hot

      • 75 - 80 degrees F. is too hot

  • Too high a temperature will result in leggy plants.

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Cabbage, Broccoli, and Cauliflower Air Temperature

  • Seeds should be started at 55 - 60 degrees F.

  • After emergence:

    • Day 65F

    • Night 55 F

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Producing Your Own Transplants


  • Avoid cool temperatures and dark conditions

    • Reduces transpiration and increases excess water problems

    • Too much water is associated with diseases which require moisture

      • Examples: root rot and leaf spot fungi

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  • Moisture

    • Ways to avoid problems with diseases fostered by too much water

      • Thoroughly water when seed

      • After emergence water in the morning so leaves will be dry before night and spot water only the dry places

  • Too little water rapidly kills young seedlings

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If reusing trays or flats

  • wash to remove any soil or plug media that may adhere to the plastic

  • dip in a 10% solution of chlorine bleach

    • 9 parts water to 1 part bleach

  • rinse trays thoroughly before they

    are reused

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  • Seedlings will need to be fertilized as soon as they emerge.

  • Avoid fertilizers with a high concentration of urea.

  • Over fertilizing can injure seedlings or promote damping-off disease.

  • Fertilize two to three times per week with the liquid solution.

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  • Tomatoes are very responsive to fertilizer and excess fertility will reduce transplant quality.

    • At every watering use a fertilizer concentration of 50 to 100 ppm Nitrogen

    • Or once every seven days - use a concentration of 250 to 350 ppm Nitrogen

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  • Peppers require more fertilizer than tomatoes

    • If feeding at every watering, use approximately 100 PPM Nitrogen

    • Increase the concentration if feeding less often.

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Vining Crops be sufficient

  • Two to four applications of fertilizer at weekly intervals, at a 100 to 150 PPM Nitrogen concentration, should be sufficient to produce good-quality vine crop transplants.

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Determining ppm N be sufficientLiquid Products

  • You need to know ppm N of the product

    • May be ppm on the label

    • May be given as percentage

  • If percentage

    • Base ppm on one gallon

    • One gallon is 3,780 milliliters (ml)

      • Round off to 3,800 ml

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Determining ppm N be sufficientLiquid Product

  • i.e. 10% is 100,000 ppm

  • i.e. 12% is 120,000 ppm

  • i.e. 15% is 150,000 ppm

  • Need to dilute to appropriate ppm for final fertilizer solution

  • Determining ppm l.jpg
    Determining ppm be sufficient

    Ci x Vi = Cf x Vf

    i = initial

    f = final

    C = ppm

    V = volume in milliliter

    1 gallon = 3,800 ml; 1 quart = 950 ml

    1 pint = 475 ml; 1 cup = 240 ml

    Determining ppm40 l.jpg
    Determining ppm be sufficient

    Ci x Vi = Cf x Vf

    If using a 12% N product (120,000 ppm) and want a 100 ppm final solution:

    (120,000 ppm)(Volume in ml) = (100 ppm)(3,800 ml) = ml of product to add to sufficient water to make a gallon of fertilizer with 100 ppm of Nitrogen

    1 gallon = 3,800 ml; 1 quart = 950 ml

    1 pint = 475 ml; 1 cup = 240 ml

    Determining ppm for 100 ppm solution c i x v i c f x v f l.jpg
    Determining ppm be sufficientfor 100 ppm solution Ci x Vi = Cf x Vf

    ml to add to water to make one gallon of a 100 ppm N fertilizer solution

    10% 100,000 ppm use 3.8 ml

    12% 120,00 ppm use 3.2 ml

    15% 150,000 ppm use 2.5 ml

    20% 200,000 ppm use 1.9 ml

    Determing ppm of dry fertilizer l.jpg
    Determing ppm of dry fertilizer be sufficient

    • Add equal amounts of fertilizer to water

      • Add water first

      • Add fertilizer to double the amount in the container

    • The resulting solution is one-half the % on the label of the dry product

      • i.e. 20% N is not 10% nitrogen

      • Do computations using Ci x Vi = Cf x Vf

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    Hardening-off Transplants be sufficient

    • Definition: Hardening-off is the process whereby transplants stop growth and develop greater tolerance to the weather so they can survive being planted into the garden

    • Is critical for both commercially grown transplants and transplants that you grow on your own

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    Hardening-off Transplants be sufficient

    • Hardening-off causes:

      • A slowing of growth

      • Greater cuticle thickness and waxes on leaves

      • Build-up of sugars

    • Ways to harden-off transplants

      • Only water the transplants when they start wilting

      • Stop fertilizing

      • Expose transplants to cool temperatures and/or higher levels of sunlight

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    Contacts be sufficient