Why start seeds inside? �

• get earlier or out-of-season flowers/crops
• rare or expensive seeds
• slow-growing/tiny seedlings
• protect from frosts, summer heat, animals, etc.
• control daylength or other conditions
• control plant location

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Direct-seeded flowers only came up at bottom of the hill 🡪

What is needed to start seeds indoors?

• Seeds!
• Growth medium and containers
• Light
• Heat (in some cases)
• Water and nutrients
• Other germination requirements
• Hardening-off
• Planning

1. Seeds:� �

1. Seeds: age/viability�Store seeds in uniform cool, dark, dry condition. Record year purchased, collected, or saved.�� �

1. Seeds: �how, when to plant? ���

2. Growth medium and containers:� �simple to complex; free to $$$; made, recycled, or purchased

2. Growth medium and containers: e.g. used tofu tubs + reused seedling trays

2. Growth medium and containers:��Or use a soil-blocker, and skip containers (try tiny, medium, and/or nesting ones)

2. Growth medium:�

• fine, light and porous
• contains nutrients or fertilized

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• bagged seedling mix
• leaf mould
• aged compost

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• garden soil (too heavy, can rot)

3. Light: Windowsills usually not sufficient

• Seedlings get “leggy” with insufficient light
• Stems may flop, break, or rot
• Not enough energy for good growth
• Seed reserves used to elongate, not for strong growth

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• Lights can be put on a timer
• 16 hours / day �(not 24 hours, plants need dark)
• Fluorescents—lower to few inches above plants
• LEDs--5 to 8 inches above plants or more
• Adjust lamp height as plants grow
• Incandescents generate heat, fire risk, �not recommended…

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• Also may put seedlings outside when warm�(BUT harden them off first)�

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• Do you need expensive LED grow lights?
• No, not for a few weeks of seed starting
• For commercial cultivation, year-round indoor growth….

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4. Heat:�

• Some seeds germinate MUCH FASTER with heat
• Warm-season crops, e.g. peppers, eggplants
• Older seeds may also benefit
• Heat mat is easiest means

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even “cool-season” plants germinate much faster at warmer temps:�e.g. compare peppers and radishes

Why?

5. Water and nutrients

• Unlike for houseplants, tap water OK (salt buildup not an issue)
• May use a dome, saran wrap, or trash bag, to increase humidity
• REMOVE when seedlings emerge (unless fancy vented dome, or if grafting)

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5. Water and nutrients

• Seeds contain enough nutrients to open the first true leaves

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• If growth medium does not contain nutrients, need fertilizer after that

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6. Other requirements for germination:

Scarification �-large, hard-coated seeds�-make seed coat permeable to water�-more important with older seeds

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6. Other requirements for germination:

Stratification

• overcome seed dormancy by signaling the passing of seasons
• usually cold + damp for 30 or 60 days
• follow seed packet guidelines�could be longer or more complex � e.g. warm/cold for Rue Anemone 🡪
• use damp sand, coffee filters, or paper towels and fridge (demo)

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7. Hardening-off

• IMPORTANT—don’t skip
• Cat is optional

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7. Hardening-off

• IMPORTANT—don’t skip
• Cat is optional

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• Start with 2-3 hours of sunlight on a warm day

>45˚ or so for onions, broccoli, etc.

>60˚ for tomatoes, peppers, eggplants, cucurbits)

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• Protect from wind at first

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7. Hardening-off

• IMPORTANT—don’t skip
• Cat is optional

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• Start with 2-3 hours of sunlight on a warm day

>45˚ or so for onions, broccoli, etc.

>60˚ for tomatoes, peppers, eggplants, cucurbits)

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• Protect from wind at first
• Gradually increase hours outside, eventually overnight (when warm enough)

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• Stems will strengthen with wind exposure

7. Hardening-off

What if you have to work?

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• Use front stoop or tree to get�morning sun and afternoon shade at first

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• Cover plants with row cover material at first

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• Start on weekend/day off

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• Other ideas?

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8. Planning

• Base garden planning on average/expected FROST DATES.�
• For now, in Hyattsville (see handouts)
• average last spring frost is ~April 9^th
• average first fall frost is ~ Oct 26^th

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• Seed-starting schedules based on number of weeks before the last spring frost:

10 wks 8 6 4 2 last frost�Jan 29 Feb 12 Feb 26 Mar 12 Mar 26 Apr 9

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Planning: life cycle requirements�Vernalization: Plants need cold period to initiate flowering. Important for:�

Plants where flowers/fruits wanted:

• many fruit trees
• winter wheat
• many spring-flowering biennials and perennials:
• Foxglove
• Coreopsis
• Columbine
• evening primrose…

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Planning: life cycle requirements�Vernalization: Plants need cold period to initiate flowering. Important for:�

Plants where flowers/fruits wanted:

• many fruit trees
• winter wheat
• many spring-flowering biennials and perennials:
• Foxglove
• Coreopsis
• Columbine
• evening primrose…

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Plants where flowering NOT wanted:

• many biennial vegetables:
• Cabbages
• Carrots
• Broccoli
• Spinach
• Lettuces
• Arugala

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Difficult to impose cold conditions on established plants…except naturally.

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Helps understand lack of flowering in first year, or if winter not cold enough.

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Planning: life cycle requirements�Vernalization: Plants need cold period to initiate flowering:�

Flowering often initiated by specific length of darkness,�for a minimum number of days.

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Initially, hours of light was thought to be the signal, thus called:

• Long-day plants
• Short-day plants
• Day-neutral plants

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Planning: life cycle requirements�Photoperiodism: �

Flowering often initiated by specific length of darkness,�for a minimum number of days.

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Initially, hours of light was thought to be the signal, thus called:

• Long-day plants
• Short-day plants
• Day-neutral plants

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Important for many mid- and late-season flowering plants, both annuals and perennials

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BUT plants can’t respond to these signals when small (“juvenile”)

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Planning: life cycle requirements�Photoperiodism: �

Cosmos = short-day plant:

• Can’t bloom when juvenile
• Once mature, need daylength << 14 hours to initiate flowering
• But in MD, day length ≥ 14 hours �early May through mid-August �(see handout)

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Cosmos = short-day plant:

• Can’t bloom when juvenile
• Once mature, need daylength << 14 hours to initiate flowering
• But in MD, day length ≥ 14 hours �early May through mid-August �(see handout)
• Direct-seeded plants too small to flower in early spring when days are short
• No flowering until days get short again
• Last year, I had 7 ft tall plants, with no flowers until late August

��this year, �I am starting cosmos indoors. �Once past ‘juvenile’, I will��i) transplant out before May, while nights still long enough,

or

ii) *cover with black-out fabric for 10 long nights before transplanting.

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*many nurseries do this

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Photoperiod requirements vary by origin, variety, breeding:

LONG DAY

• Dill
• Rudbeckias
• Cosmos astrosanguineus
• Dianthus/Pinks
• Salvias
• Bachelor Buttons
• California poppy
• Sweet peas
• Lobelias
• Cleome “pink queen”

DAY NEUTRAL

• Peppers
• Cucumbers
• Tomatoes
• Dianthus/Sweet William
• Impatiens
• Geraniums
• Alyssums
• Valerian
• French Marigolds
• Cleome “rose queen”

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SHORT DAY

• Basil
• Corn
• Cosmos bipinnatus
• Cosmos sulphureus
• Dahlias
• Chrysanthemums
• Gerbera daisies
• Cardinal climber
• African marigolds
• Cleome spinosa

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• Calendars and timing—see handouts
• Miscellaneous—

Fungus gnats?

Damping off?

Other pests, problems, or questions?

• Tomato grafting—anyone?

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Why graft tomatoes? �For disease resistance, vigor, and improved yield in heirlooms and other varieties.�

Grafted

Not grafted

Arkansas Traveler tomato plants

• Calendars and timing—see handouts
• Miscellaneous—

Fungus gnats?

Damping off?

Other pests, problems, or questions?

• Tomato grafting—anyone?
• Demo/look/try:
1. Soil blocker (on porch)
2. Homemade light bench
3. Soil-less radish starts for immediate planting
4. Scarification with sandpaper
5. Stratification (in fridge)
6. Hardening-off seedlings (porch)