Bulb Predators / Raised Beds

Rodger Whitlock totototo@pacificcoast.net
Mon, 27 Sep 2004 10:30:22 PDT
On 23 Sep 04 at 11:03, Ann Marie wrote:

> What is "plunge"
> Briefly you make a structure, lay hardware cloth on the bottom, add
> gravel on top, place plastic pots in the order you want, add plunge
> around them and then plant your bulbs in plastic pots of the same
> size to nest in the pots in the bed.

In my experience, a plunge bed's great advantage is the even 
conditions it provides to the plants: both temperature and moisture 
levels are kept very even, though of course changing with the 
seasons. It is my belief that many plants detest the drastic changes 
in soil temperature and moisture content that ordinary pot culture 
entails, and do much better with more even conditions at the root.

I used ordinary sand as the plunge material; put the plants in *clay* 
pots, not plastic; and had the plant pots directly in contact with 
the plunge material. The bed of sand wicks up any excess moisture, so 
overwatering is almost impossible, but at the same time acts as a 
reservoir so the pots don't dry out at all easily. 

Note that this has more than a passing resemblance to the "capillary 
beds" one finds sometimes described in the horticultural literature.

Ann Marie's recommended method will control temperature variation, 
but the use of gravel (not water retentive), plastic pots 
(impermeable to moisture), and nested pots (breaking any capillary 
contact between plant pot and plunge material) all work against 
getting any useful control of the moisture level in the pots.

Some bulbs definitely do not like intense drying off. Iris 
winogradowii has never grown as well for me as when it was in a large 
terracotta pot plunged in sand, and watered with yesterday's cold tea 
first thing every summer morning.

As for the "structure", make it strong and make sure the sides won't 
bulge. The easiest way of doing this is to make sure the 
"structure" isn't too big. The best I've had was an 8'x4' bed made of 
railway ties stacked on the flat. Longer beds made with railway ties 
would start to bulge in the middle of the sides sooner or later.

Also, you don't need much height: 12-18" is quite adequate for most 

As with raised beds, you do not need to excavate underneath or 
install drainage. As long as the plunge material is in capillary 
contact with the native soil, all is well.

Rodger Whitlock
Victoria, British Columbia, Canada
Maritime Zone 8, a cool Mediterranean climate

on beautiful Vancouver Island

More information about the pbs mailing list