Depth and California bulbs
Jane McGary (Thu, 10 Nov 2011 11:04:07 PST)

Regarding how various western North American "bulbs" grow down and
sideways in the soil, it should be noted that Calochortus have true
bulbs, while the other genus under discussion, Dichelostemma
(Themidaceae, a split from Alliaceae), has corms. True bulbs descend,
I believe, thanks to contractile roots; you can see these when you
lift the bulbs. The contractile roots will be withered at that time
and look like wrinkled tubes. It seems to me that I've seen
contractile roots on corms too, but I can't recall just which genera.
Some bulbous and some cormous plants also form offsets on annually
produced stolons, which would explain the situation one correspondent
noticed. Stoloniferous offsetting can be uncommon in a genus; for
instance, there are a few Crocus species that do it, and I can think
of one Fritillaria (F. pontica) that does. In Erythronium, the
eastern American species are stoloniferous, but the western ones are
not, as far as I know. One reward of growing bulbs in pots is that
you get to observe what goes on underground closely, but I'm happy to
have left most of the repotting behind, as making up the soil mix
each summer was a huge task.

Another way that Calochortus increase is by stem bulbils, which form
in the axils of the leaves. If the bulb is at sufficient depth, these
bulbils form below the soil surface and add another strategy for
survival. When you're cleaning up your Calochortus, you should always
check along the dry stem for bulbils, which can be detached for
planting and will produce flowering plants a year or two sooner than seeds.

Dichelostemma capitatum, the species mentioned in a previous post,
does make detached offsets, but D. ida-maia, the popular "firecracker
brodiaea," has a lot of small offsets clustered around the parent
corm. Both of them self-sow freely, as do some other themids. The
production of numerous offsets in the western American themids is
probably an adaptation to predation by burrowers such as gophers and
diggers such as bears and humans; the tiny offsets are likely to be
missed by the hungry mammals. This characteristic also makes them
good for nursery production and subsequent mass planting in gardens,
where their long-lasting, colorful flowers are much appreciated at
the end of the "bulb" flowering season. They're especially well
adapted to planting in rough grass. I recently put some dozens of
Brodiaea californica in a patch of seasonal fine-textured grass on a
high bank in my new garden. I had raised this large, showy species
from seed in a mesh basket kept plunged in sand for a couple of
years. Dichelostemma capitatum went into a bioswale or "rain garden"
in the new garden, as I've seen it in vernally wet meadows. It's a
lovely rich lavender color accented by dark stems. Other themids in
the garden here add early summer color in a bed with a lot of
colchicums, whose foliage will be up when the themids are in flower.
I have admired these plants ever since childhood, when Triteleia laxa
was my favorite meadow wildflower in California. Telos Rare Bulbs
offers some of the less common species, and a few kinds can be found
in mass-market bulb catalogs. They are very easy to raise from seed
and flower mostly at three years.

I suppose if you find your bulbs migrating to the sides of pots, the
roots may have gone that way seeking extra moisture, and pulled the
bulbs after them by contracting. If you use a soil mix with a lot of
peat or similar organic component, it tends to draw away from the pot
as it dries, and then overhead water will run down the sides instead
of penetrating the soil evenly. That's one reason I prefer a mix that
is predominantly coarse sharp sand, even though it makes the pots quite heavy.

Jane McGary
Portland, Oregon, USA