wintering-over Spring bulbs in pots

Gene Mirro
Mon, 26 Dec 2011 11:29:25 PST
"When  we were discussing this topic, Gene Mirro wrote " I grow Dutch bulbs in a mix of bark, sand, and garden soil, with some lime and bone meal mixed in.  They love it. "

Gene, can you tell us a bit more about this? I've been doing this with lilies for a few years, and so far the results are good. So far I have not tried it with other bulbs. What sort of year to year performance to do you get? Do tulips take well to this treatment over the long run? How about Dutch and English iris? Do you use any supplemental feeding other than the bone meal?  Do you dig the bulbs for the summer or make some other effort to keep them dry?"

A big problem is temperature control of the root zone.  The pots need to be plunged in sand, soil, bark, etc.  The bigger the pot, the better.  I always feed Dutch bulbs with lime and and a little NPK fertilizer in early spring.  I don't usually apply bone meal beyond adding it to the mix.  I add bone meal to my mix for all plants, because it makes big, healthy root systems.  With tulips and Calochortus, it's important to keep the mix moist while the foliage is green, and then to let the mix dry as the plant goes dormant.  This is not so easy.  It's amazing how long the mix will stay wet after the foliage dies off.  So I let some weeds grow in the pots, and they dry out the mix and die off before they set seed and become a problem.  Or you could sow some fast-growing annuals in the pots.

I think the Doug fir bark has chemicals which control pathogens.   I've noticed that mix with Doug fir bark reduces problems with basal rot on lilies.  I've seen academic papers on this subject.  Also, the Doug fir bark is not as water-retentive as peat, and tends to reduce the available Nitrogen level in the root zone.  All of these factors may be helpful, but I'm speculating.  

Year-to-year performance:  I don't usually keep Dutch bulbs potted for more than one season, but tulips do very well in that one year.  The bulbs add weight, and sometimes divide.  I do keep Calochortus in pots for years, because SW Washington state is not a good place for them outdoors.  They do well.  I don't dump them out over the summer; too much work.  Don't forget to fertilize every spring.

I have terrible problems growing lilies in pots.  They do fine until hot weather arrives, and then they all get basal rot and die.  I grow species only.  Maybe the hybrids are tougher.  So I have a firm policy of starting lily seedlings in pots, and then transplanting them into the garden as soon as the weather and soil are ready in spring.  No more basal rot.  Even in the garden, the lilies have to be mulched and/or grown with companion plants to keep the soil cool and dryish.  I often let them grow to flowering size in a crowded clump.  It doesn't seem to hurt them.

I can't give strong scientific arguments for these practices.  On the other hand, they don't contradict the science that I am aware of.  If something works, I keep doing it.  Lilies in particular have provided many unpleasant learning experiences.  When lily people say that the soil needs to be cool and shaded, they are not kidding.

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