Friday, December 9, 2011

Warning about "pre-cooled" lily bulbs in Fall/Winter

"Pre-cooled", "Pre-chilled" "Ready to Grow", "Southern Hemisphere", and "Vernalized" lily bulbs sold and delivered late summer through winter are intended for the cut flower forcing trade - not the home gardener.  These are all buzz words to let the commercial greenhouse grower know that the lilies have undergone an artificial  "Winter Chill" and that they are ready to begin sprouting immediately upon being "thawed" from their cold storage cases. 

Bulbs marked as above were dug during the previous year, packed in peat or shavings and slowly dropped to below freezing in coolers for storage.  It takes a minium of 2 months of "winter chill" to reset the flowers properly, so if you are purchasing bulbs that seem a bit early for a natural fall harvest in mid to late September, then those bulbs most likely have spent 12 - 15 months (or more) in a freezer and are "old crop".  Prolonged storage will sometimes kill the tiny sprout within the bulb - the reason why high end greenhouse growers will insist upon the "current crop".  The only way to check viability is to slice open the lily bulb and if there is a black or dark colored "streak" in the center, the flowers have been killed.

"Pre-cooled" ready to plant lily bulbs require anywhere from 90 to 120 days of continuous non-freezing weather to grow and bloom - which eliminates any gardener whose winter temperatures include more than just a light frost during that time period.  Once thawed, you cannot stop their growth, after all, they are simply doing what nature intended - grow. 

Should you have bulbs that are emerging now - in a colder climate - there are a few things you can try to save your investment.  After the soil freezes - either pile more mulch over the emerging sprout to try and slow them down, remove them from the garden and pot up to move to a heated greenhouse, or let the frost kill back the sprout and wait until spring.  Lily bulbs are depleted while the sprout is growing and the bulbs become smaller in size, if the sprout is killed then there might be enough bulk left to send up a new sprout when the weather warms in spring, but it is chancy.  If the bulb has not outright died over winter, it might come up with a blind stem (no flowers) next summer and should be able to recover enough to bloom a year later.

Pre-cooled (not pre-sprouted - that is another topic) lily bulbs in the spring are OK - and you can plant before the last frost because it will take some time for the lilies to emerge and a few degrees of light frost followed by warmer day temperatures will do no harm.  

[ UPDATE - December 21, 2011 - Email correspondence to a southern gardener (near the Gulf) that we thought might be helpful to others.] 

You are probably OK if you planted the lily bulbs 6 to 8 weeks ago and they are not emerging.  Being in the south, your winters are usually not as severe as in the northern climates where we have repeated freeze-thaw, with temperatures that drop suddenly into the teens and lower during early winter.  Spring frosts are not as great an issue, so if your bulbs behave themselves and stay underground until at least early February, and then you should be just fine.  The blog post was to help people in more northern climates.  In one day I had several panicked phone calls from the Midwestern states.

The biggest problem with planting "pre-chilled"  lilies out of season is if the soil temperature is warm (as in fall), then the bulbs think it’s "spring" and start growing fast with tender cells.  If emerging sprouts are hit by rapidly dropping temperatures in early winter while the sprout is tender, you will lose the bloom.  Lily bulbs kept on a natural cycle are waiting for freezing temperatures so as to go into semi-dormancy and reset the bloom for the next season.  They do not sprout until the soil has begun to warm up again.  This is the reason for pre-cooling lily bulbs for forcing; they need to come up and quickly flower to reduce greenhouse heating expenses.  Bulbs intended for the greenhouses were already "frozen" so they can be fooled into thinking it is spring.

If emerging sprouts are only subject to temperatures in the low 30's for a night or two in
spring, they are generally OK.  I've had lilies up here in the Pacific Northwest more than a foot tall with frost in spring and it usually only damages the leaves (browns them a bit) but they continue to grow, this is because they were used to the temperatures already hovering around freezing underground and the cells are  toughened.  During a gradual drop in temperature frost is less likely to have an effect.  

In general, Asiatic lilies can take "late spring" frosts better, OT (Orienpet) lilies show more frost resistance than the Orientals, but purebred Trumpet lilies might look like sticks covered in wet seaweed after a late spring frost and will not recover that summer.  

I'll post more about late frosts and emerging lilies in spring.  -Dianna

1 comment:

  1. Thanks so much for the info! I have learned the hard way. I have sprouts (or should I say frozen sprouts) What I thought was a bargain has become a nightmare.

    I'll only buy from YOU now!!!