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Cold frames and summer dormant bulbs
Why cold frames?
• Residential houses are typically too warm: cold is essential to the proper development of flower buds.
• The open garden in our climate is too cold.
• The severity of our winters is exacerbated by the lack of consistent snow cover: cold frames can mimic a good snow cover.
Why cold frames?
• Moisture control, particularly at start of dormancy
• Pest control: deer, rabbits in particular• Flowers last longer when not exposed to
the weather• Protected frames allow the culture of
plants not suited to the open garden• Plants will bloom long before similar sorts
in the open garden.
Cold frame management
• Like a dog, they require attention at least twice a day, and this might not agree with your work schedule.
• Must be open when the sun is shining on the frame.
• Cover the frame in severe weather.
• Site protected frames near buildings or other sheltered areas.
Pots vs. baskets vs. planting in the ground
• Pots require careful watering.
• Clay pots will benefit from plunging.
• Black plastic pots heat up in the sun.
• Baskets take more room but allow free root growth.
• Reserve planting in the ground for plants which resent disturbance or for plants with massive root systems.
Media
• General: mix of pine fines, perlite and loam
• Reduce the loam for plants which require sharp drainage (fritillaries, some Narcissus).
• Increase the loam for plants which are water tolerant (aroids, amaryllids in general).
Watering
• Water once heavily in October to get things going.
• Water again when plants come into active growth (stems elongating, leaves expanding, buds developing).
• When the last petals fall, stop watering for the season; with some western NA bulbs, stop watering about a month before bloom.
Old adage of bulb growers
• These plants like to mature into a drought.
• Many plants will be ripening in late April or May: these are rainy periods for us as a rule, so be prepared to KEEP OFF RAIN while the bulbs are ripening.
Ripening
• Newly dug bulbs are full of moisture: before being stored for the summer, bulbs must be allowed to lose some of this moisture.
• To allow moisture loss, spread the bulbs out in a shady place protected from rain and vermin. For potted bulbs, simply do not water the pots. After about two weeks, they bulbs should be ready for storage.
Summer conditions
After suitable ripening and moisture loss: • In the rain-shielded frame in pots• Out of the soil and dry in paper envelopes• Wrapped in newspaper cocoons • In zip lock plastic bags for suitably ripened and dried
bulbs. • Hot, dry summer conditions suit most of the bulbs
discussed here.
• NEVER STORE MOIST, NEWLY DUG BULBS OF THE SORTS BEING DISCUSSED HERE IN PLASTIC BAGS.
Bulbs wrapped in newspaper
Simple cold frame construction 1
Cold frame construction 2
Cold frame construction 3
Cold frame construction 4
Cold frame construction 5
Cold frame in use
Rhodophiala bifida
Nerine sarniensis ‘Corusca Major’
Biarum davisii
Colchicum variegatum
Colchicum ‘Disraeli’
Ambrosina bassii
Crocus pallasii
Iris unguicularis
Narcissus cantabricus
Tecophilaea cyanocrocus
Freesia viridis
Scilla greilhuberi
Scilla peruviana
Asphodelus acaulis
Early garden crocuses
Adonis vernalis
Crocus ‘Blue Pearl’
Gymnospermium altaicum
Iris ‘Katharine Hodgkin’
Crocus ‘King of the Striped’
Iris graeberiana
Iris rosenbachiana
A hybrid oncocyclus iris: Iris kirkwoodii × I. hermona
Iris ‘Dardanus’
Tulipa humilis
Corydalis popovii
Fritillaria eastwoodiae
Fritillaria bucharica
Fritillaria tubiformis
Fritillaria pyrenaica
Fritillaria biflora ‘Grayana’
Fritillaria ehrhartii
Fritillaria stribrnyi
Muscari dionysicum
Tulipa saxatilis
Calochortus tolmiei
Calochortus superbus
Calochortus ‘Golden Orb’
Dichelostemma ida-maia
Dichelostemma volubile
Dichelostemma capitatum
Bellevalia longipes
Bellevalia longipes