Crocus cultivation in containers

[Croquin]

There has been some discussions between amateur saffron growers about the possibility to grow Crocus sativus in containers.
I was reported about one unconclusive experience with outdoor cultivation in containers: corms would produce flowers on the first year, but the subsequent year, they seem to be unhappy with the environment conditions, stop flowering and produce much smaller corms.

Now I understand that many of you grow crocuses indoors (greenhouse), therefore in containers, and that it does not seem to be an issue at all.
I have not tried myself, but I was asked the question again recently and I'm not so sure about what to answer, or why this experience did not work.

Can anyone of you provide me with information on this topics ?
Especially if you are used to grow cousin crocuses of C. sativus in containers.

Thanks !

[Gerry Webster]

All the saffron group grow well for me in containers. Just feed them well.

[Croquin]

How do you manage the situation Gerry ?
For instance: size of the container, amount of corms per container, type of growing support, where to place the containers, etc.
This will be useful to a friend.
Thanks on his behalf.

[Maggi Young]

Croquin, the Bulb Log may have notes about several of the Saffron Group Crocus and how they grow here in Aberdeen -http://www.srgc.org.uk/logs/index.php?log=bulb
 the index is here http://www.srgc.org.uk/logs/index.php?log=bulb

[Gerry Webster]

How do you manage the situation Gerry ?
For instance: size of the container, amount of corms per container, type of growing support, where to place the containers, etc.
This will be useful to a friend.
Thanks on his behalf.

They are grown in 10cm diam. clay pots; the mix is equal parts of JI3 & 6mm grit/Perlite. The pots contain as many corms as will fit in, nearly touching. They are watered at the beginning of Sept., then are kept in an uncovered sand plunge & only brought under glass when flowering. They are fed weekly with 1/4 strength high potash fertiliser. When the leaves die down they are kept covered & completely dry. They are re-potted every year, which is probably unnecessary.

[Croquin]

Thanks for your answers.

Maggi: what an amount of work for compiling all this !!!!!!!!!!!! 

It seems that there were issues with C. sativus, back in the early 2000s for (i) reproducing flowering corms and (ii) getting them bloom each year.

(i) From what I have seen in your pictures (34/06), the planting depth is not enough.
Planting C. sativus corms near the surface will result in the production of a big amount of cormlets, but they are small and do not produce flowers (minimum corm size for flowers is 8g/8cm circumference: 1 flower; 3 flowers with 15-20g/10-12cm corms).
However, these cormlets are the best to get corms of good size after 1 year cultivation in proper conditions.
Recommended planting depth is 15 to 20 cm for this species (I think 20 is a bit too much though, target 15 and adjust depth to corm size, deeper for big corms).
At that depth, you will get few corms, but bigger ones.
Cormlets can be planted 10 to 15 cm depth, not less.

A second parameter is the strain you use.
Bulbicultors have mecanically selected a strain producing a huge amount of corms, which do not specifically produce good saffron crops, nor very big corms.
Probably starting with a mixed population of individuals producing few corms and individuals producing a lot of corms, their practice resulted in a stock increase of the fast reproducing strain.
If you have such a strain, do not expect getting few big corms ever.
Rather buy corms from saffron growers in the mediterranean countries (carreful with corm diseases like fusarium and rhizoctonia, often occuring in some countries).
Their strains usually produce 1 to 3 big corms, hardly more.

(ii) For getting flowers each year, the corm needs to be kept in warmth during flower embryogeny (mid of June to mid of august).
Optimal temperature is 23-25°C.
Below 21°C and over 27°C, flower rate will decrease.
I think that you will get nothing if corms are kept at 15-17°C, whatever the corm size.


(PS: is the spell-checking tool working? I am surprised that it never finds anything)

____________________________

Gerry: I have seen in the files pointed by Maggi that they also grow crocuses in plastic containers, is it important to have clay or plastic pots ?
The directions you give, are they for crocuses in general or specifically for C. sativus ? (I ask because 10cm diameter pots implies limited depth - see my comments above).
What is JI3 ?
Do you get corm diseases sometimes and how do you get rid of it ? (it is probably a good thing to re-pot each year - for corm development and for decreasing the risk of sanitary issues).
I have seen in various pictures presented on this forum that people cover the soil surface with stones, what is is used for ?

[Gerry Webster]

Croquin - I have grown & flowered C. sativus in the manner I described though I no longer have it. So far I have had no problems with disease. I've never used plastic pots. JI3 is a  potting medium - devised many years ago at the John Innes Institute & available commercially in the UK. It is supposed to consist of loam, peat & grit sand in the ratio of  7:3:2. I suspect most of that available today is not as it should be but it seems to work well enough.

[Croquin]

Thanks Gerry, it seems possible to grow and flower C. sativus successfully in pots - why would it be impossible after all ?
Mediterranean sunny Brighton climate surely helped you have good flower preparation during summer.

What planting depth did you use with C. sativus ?
Did you observe abundant production of smaller corms as reported in Young's files ?

Are your pots exposed to frost (what minimum temperature) ?

[ronm]

 These people obviously have no problems with it, 

http://www.thompson-morgan.com/flowers/flower-bulbs/crocus-bulbs/crocus-sativus/t10892TM

Personally I find C.sativus very difficult to flower, unlike the rest of the 'Sativus' types which are easy,  . Possibly a clonal problem as has been stated previously on this thread.

[Gerry Webster]

Croquin- Planting depth - as for all crocus - 7-8cm. I haven't observed lots of small corms. I don't know  what the average minimum temperature is here; in the last two winters pots have probably frozen.
It may be that different clones of C. sativus behave differently.

Currently, I only have the following saffron crocus: CC cartwrightianus, hadriaticus & thomasii. I have no problems with any of these.

The description of Brighton as "Mediterranean" is now something of a joke.

[Croquin]

ronm: of course they don't, it is a business 
It may be a clonal problem, it may be due to the cultivation conditions.
Incubating dormant corms in warmth is probably essential in northern countries.
It may happen naturally, for instance if you forget the pots in the greenhouse during summer.
Try it this summer by placing unpotted corms in a warm place (probably indoors) - not more than 27°C.
The species blooms generously, even small corms may go mad.

Gerry from sunny Brighton 
7-8 cm is a suboptimal depth, but you had good results, it means it works.
I read a paper where it was stated that C. sativus corms are endangered as temperatures reach 0 or -1°C, and are irreversibly damaged by -2°C.
I was a bit scared when we got -20°C last winter.
Leaves burnt despite the snow cover, and frost went underground as deep as 50cm according to a friend who was excavating somewhere around.
But to my surprise, corms (starting to grow as soon as november) are very healthy and well developped this season.
Only those dropped on the surface of the ground (experiment) died of frost.
That your pots got frozen is another observation confirming that probably, the chemical composition and the corm structure of the plant in vegetation is not the same as that of dormant corms (example: starch content is very high during summer, but no trace of it during winter).
Only dormant corms would be frost tender ?
Whatever - thanks for the discussion on cultivation possibilities in small pots, I hope I also gave some tracks to follow for making your C. sativus bloom each year, even in sunny Scandinavia.

[Janis Ruksans]

I have only a pair of pots with Crocus sativus originally collected on cultivated field in Iran. I use plastic pots 15x15 cm, 20 cm deep. In it I place 5 large corms of C. sativus, appr. 5-7 cm deep. Soil mix is 2 parts coarse sand, 1 part peat moss, 1 part loam. Top dressing 1-2 cm of stone chips. Pots are kept all the year round in greenhouse. Temperature in summer up to 35 C or sometimes more. In winter up to minus 35 C but pots are covered with 5 cm thick glasswool sheets. Watering from September every week with 0,2 % solution of Cristalline - in autumn high potash variant with all microelements. Watering usually stopped when weather became cold. In spring it starts after taking off cover with defrosting of soil, first month with slightly higher nitrogen, after that with high potash variant of cristalline (cristalline - helat based easy soluble fertilizer). Frequency - 1-2 times in week, depending from weather. When leaves start to yellow watering is stopped. Annual repotting applied. Blooming very good, corms formed very large. Repotting done immediately after harvesting - corms stay out of soil usually only few hours, not more than one day. The same applied to all members of sativus group (really to most crocuses, exception is wet-condition growing species) and most of them grow very well.
Janis

[Croquin]

Janis, you get very cold temperatures in winter - you have mentionned as low as -35°C.
I'm curious to know how low a temperature could C. sativus survive: did you ever get any measurements of this, eventually on species from the same group?

I have observed frost burns on the leaves when temperatures go below -15°C (only natural protections such as snow cover if any, crocuses are in open field).
I never had below -21°C and C. sativus did not suffer more than that: corms are planted deep underground where the cold gets moderated.
It is not the case in pots (although I do not have any idea about the thermal protection you apply).

A few of you have now mentionned very shallow planting with very good results.
I know a saffron grower advising 10cm depth for outdoor cultivation (however, he is in a warm part of the country, and he lifts corms every year).
Others recommend planting depth between 15 and 20cm (corms lifted every 5 years).

I must admit that I get the best corm development around this value.
Shallow planting resulted in numerous small corms and more pest issues - but we are now talking about different cultivation conditions (ground/pots).

Is your saffron good, did you try it?