cosmos atrosanguineus

Johannes-Ulrich Urban
Sun, 24 Mar 2013 08:48:00 PDT
Bonjour Denys,

Cosmos atrosanguineus has tubers like a Dahlia but these are much more
fragile. They do not take a totally dry situation like let's say in a
box or paper bag in winter and are best kept in dry compost in a big pot
in a cold and dry but frost free storage. It is a good sign that white
little rootlets appear all over the tubers as often comercially
available tubers are already dead on purchase, yours are definetly

The "welded" part is where the shoots will arise so this should be
planted upward but still about 3-5cm below ground. Take care not to
separate any of the tubers from the point where they are attached to the
central shoot area as a tuber without an "eye" will produce roots but
not a shoot and will therefore eventually die. If the separated tubers
you talk about would have a bud at their tip they will grow but
unfortunately most of the detached tubers do not have that bud.
If you are unsure which end is which in the detached ones I recommend
planting them horizontally and cover entirely with compost about 2cm

How long will it take from now on to have frost free weather in your
garden? I am asking this because if you start these kind of plants
indoors too early they will need a lot of attention and care and tend to
etiolate which makes them vulnerable to direct sun and wind when planted
out in the garden after the risk of frost is over. The shoots of this
Cosmos will not tolerate any frost. You could delay sprouting by putting
the entire tuber into a plastic bag and put it into the vegetable drawer
of you fridge, BUT DO NOT FREEZE IT. Take care that there is not too
much condensation in the plastic bag (a little is beneficial) and do not
add any water by all means and check for mildew from time to time.
(my fridge contains all sorts of things like that except food....)
I would start a Cosmos indoors in a pot about 4 weeks before the end of
frost danger or plant it directly in the garden about 2 weeks before the
last possible frost (this is for European mild winters, where the soil
is frost free a long time before the last air frost) Never plant into
frozen soil.

Good luck!


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