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

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