Best soil for a raised bed?

Pamela Slate
Sun, 13 Jul 2014 12:06:12 PDT
Hi Mike,
I've been growing bulbs similar to yours (Amaryllids, Irids, Hyacinths,
etc.) in raised beds for about 14 years so I've "played" with a number of
soil mixes and some with disastrous results. The 12 beds are made of
concrete block and are 25 inches tall topped with cap block.

Hands down, the mix that has worked best for all plants, including bulbs
and veggies/herbs, has been roughly a third sandy loam, a third compost
(from a pesticide/herbicide-free source) and pumice. Proportions have never
been measured exactly. From the bed bottom up, the mix is rototilled
thoroughly using a Mantis. The soil is loose and drains perfectly.

My garden is just 2 mi.south of Carefree AZ, at about 2400' elevation with
slightly cooler temps than the rest of this area, especially in winter.
Definitely the nights are cooler and there is generally more rain and also
frost in most winters.

Unless you consider tarantulas pests, my only pest challenge has been grubs
and I've used beneficial nematodes that have controlled them successfully
(but not all of them are the same and contact me privately if you'd like
further info).

My only question for you is depth of your bed. Are you sure it's deep
enough for the growing season and will you later regret not adding another
level in the event you decide to add plants that require deeper root run?

FYI, a couple years ago I decided to begin eliminating as many containers
as possible and planted some common Lachenalias in one of the beds. Not
only did the bulbs increase much more than in pots but the bulbs were much
larger with denser roots...flowering was better too. And if you wonder
about Ferrarias, go to the wiki and check out the photos of my increases of
F. crispa that were left in the beds. I've found bulbs to be more than
extremely forgiving!

Whatever mix you use, I would urge you to water the vacant bed, the
frequency depending on your rainfall, because with all the aeration created
in mixing, it will sink over time. Also, in my experience, allowing a
"curing" period for the mix, has in some cases, resulted in greater

I have no doubt your bed will be glorious. What a fun project!

Good luck,
Pamela Slate

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