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