Crocus Cultivation

[tonyg]

Here is a new place where I would like to invite all crocus growers to share their experiences of how they grow crocus.

It would be especially interesting to hear about successes in the garden  rather than in pots.  Which species have done well and also those which have failed.  Several forum members have shown us some nice plants in their gardens but it can be hard to locate the information within the 'busy' crocus threads.

I will start it off with a summary that I am preparing for the Glasgow Conference.  It is not the finished article yet so here is your chance to contribute!    

The successful cultivation of crocuses depends on several variable factors.  Firstly we have to consider the native habitat and climate of the plant under consideration.  Then there is the issue of where we are to grow it, both geographically and within the garden.  Factors relating to the climate which the plants experience in their native habitat can be related to garden conditions.
The grouping below is a personal one, based on my experiences in the dry SE of England.  When considering where to site these plants in your garden local factors should be considered.  Crocuses are plants that enjoy a sunny exposure.   Even those which require year –round moisture need sun too.  Most are frost hardy but prolonged exposure to extreme cold can cause damage to the foliage which weakens the plants.  Prolonged freezing at the corm or root level should be avoided.  Given a sunny site and a well drained soil most of the group A crocuses will succeed outside.  In warmer and sunnier locations most of the group B crocuses should also grow well although some are more difficult to please than the Group A plants.  However these will usually do better given some protection, in ideal conditions under cold glass these and the Group C plants are most successful.  The Group D plants are growable under cold glass in SE England but are not as vigorous as the Group C plants.  Group E are recognised as more difficult while I have little or no experience of those in Group F!

A: Tolerant of summer moisture – suited to maritime gardens: Cc vernus, tommasinianus, kosaninii, etruscus, versicolor, imperati, malyi, corsicus, minimus, kotschyanus, vallicola*, gilanicus, ochroleucus, dalmaticus, angustifolius, cvijicii*, gargaricus*, rujanensis, flavus, speciosus, pulchellus, laevigatus, tournefortii, banaticus*
B: Tolerant of some summer moisture – need a drier rest to thrive: Cc cambessedesii, longiflorus, serotinus, medius, niveus, goulimyi, hadriaticus, reticulatus, sieberi, robertianus, ancyrensis, cancellatus, biflorus, chrysanthus, danfordiae,  cyprius, aerius, pestalozzae, caspius, paschei, adanensis, leichtlinii, alatavicus, korolkowii, michelsonii, olivieri, antalyensis, candidus, fleischeri, boryi
C: Need a warm dry rest – much more likely to grow well with protection: Cc cartwrightianus, pallasii, thomasii, oreocreticus, asumaniae, mathewii, hermoneus, graveolens, carpetanus, nevadensis,
D: Difficult (Semi-desert, questionable hardiness): Cc hyemalis, aleppicus, veneris,
E: Difficult (High mountain plant): Cc baytopiorum, scardicus*, pelistericus*, scharojanii*, abantensis,
F: Little grown – Cc autranii, karduchorum, moabiticus, siehieanus, almehensis, hartmannianus, kerndorffiorum, wattiorum, vitellinus, boulosii,
*Prefer not to be dried out completely at any time.
These artificial categories do not take account a taxa which have a very wide distribution and/or grow in areas with differing climatic influences.  In these cases eg C laevigatus and C serotinus, there are some forms which are significantly better garden plants than other forms.

Composts (for pot growing)
Much has been written about choice of ingredients for compost mixes.  However, just as important as the mix is how you manage watering and feeding.  There is no substitute for personal experience, each grower should develop a watering strategy to suit their own compost and growing conditions.  The compost should be moisture retentive but free draining and contain enough nutrients for the long growing season.  I use a mix of roughly 50% John Innes No 3, 45%sharp grit or gritty sand,5% perlite.  To this I add bonemeal for a slow release feed during the growing season supplemented by a high potash feed in late winter.  Following Ian Young’s approach I add a small quantity of Sulphate of Potash to each pot and water it in.  This high potash feed boosts the plants at the time when the new corm containing next season’s flower buds is developing.

[David Nicholson]

Tony, good thread idea, I have learned from your notes already. I hope to contribute after return from holiday.

[ian mcenery]

Tony a very useful document which has summarised information which is sometimes in other published detail not user friendly. It also shows me why I might be having difficulty with some plants. Hopefully as the season progresses we can all add our experiences and thus all gain from the triumphs or disasters of others

[Anthony Darby]

An excellent thread. Wouldn't do any harm to link it to your superb web site Tony. In fact, linking each species to its page would be cool (but perhaps time consuming) ?

[Boyed]

Tony, thank you very much for your wonderful article. I found it very useful.

I would like to add some notes from my experience. Relating composts, I don't use a special prepared one and don't use fertilizers at all. I just take a rich leafy soil under the trees from forest and my all crocuses do perfectly in this soil and grow huge bulbs increasing rapidly, while the ones planted in garden soil don't do that well.

And also one more thing; I noticed that some species, which prefer dry summer rest, also do well if planted in moist positions. I have watered my crocus pallasii all the summer and it developes very well, flowering and increasing abundantly. I pereodically do experiences with my crocuses trying some in the conditions they stated not to prefer and sometimes they do well. But, fore example, I didin't succeeded by providing a dry rest for crocus heuffelianus. It bloomed, but the ones having enough moist during summer developed much better being quite vigorous.

[Luc Gilgemyn]

Great initiative Tony

Brrrravissimo !

[tonyg]

Very interesting Zhirair, your comments are just what I hoped we would hear.  It is good to experiment, I have plans for more experiments with crocus in the garden here.  (But we hope to move house next year so for now most of my crocuses stay in pots!)

[ChrisB]

After attending the Dunblane lecture earlier this year, followed by the Irid Day AGS put on last weekend, I've become a bit more interested in crocus than I was so I bought one or two from Pottertons on Saturday.  The information you have posted here Tony is very valuable to someone like me, and I shall cut and paste it into my word processor so I don't forget where it is, for future reference!  Thank you very much.  I must check detail about depth of planting on Ian's site too.  Probably about as important as the soil mix?

[Otto Fauser]

Tony ,an excellent and most helpful thread ,even for gardening in the antipodes. All my Crocus are grown in the open ,[none in pots] ,under trees and shrubs and the rarer & more difficult ones in bulbbeds- so all of them receive the rain that comes from above all year round.Some summers be very dry and some quite wet.Those growing under trees and shrubs benefit from leafmould ,those in the bulbbeds get an annial topdressing of leafmould and coarse sand, plus complete fertilizer in late autumn and also a dusting of sulphate of potash in early winter.
  Some of the easiest species and selfseeding abundantly[ apart from the obvious like tommasinianus , kotschyanus,speciosus]whether in dry or moist condition are banaticus, rujanensis ,and  caspius ,grown from seed that Paul Furse sent me in the 1960's.
 Cr.autranii ,karduchorum ,sieheanus grow well but do not set seed or multiply-Cr. moabiticus , aleppicus, michelsonii, kerndorfiorum only last for a few years in the open ,I should grow them under cover.Some of the rarest ones I have never grown - just not available in Australia -like almehensis, hartmannianus, boulosii, so can't report on these .Maybe one day i'll be fortunate enough to try these ,I know of only one person who grows boulosii[ not a very exciting species ],namely Erich Pasche in Germany.
     looking forward to many more comments and helpful hints
        Ciao Otto.

[Thomas Huber]

Although I don’t have such a long-lasting experience like Tony and Otto, I will try to bring in some helpful hints for this wonderful thread.

I have ALL my plants in the open garden (except seedlings). For this purpose I have created a rock garden with well drained soil. Starting soil was loamy and heavy. I have added lots of sharp sand, limestone grit, leafmould and pumice to make it lighter. Each species is planted in a lattice basket in which I fill some cm of soil, then a layer of fine grit (2-3 mm) in which the corms are placed. Then another layer of grit and the rest is filled up with soil again. This gives the corms a very well drainage and avoids permanent contact with water, which could cause rotting during dormancy.

Crocus that are told to be tender, are planted near the house wall, which makes it easy for me to protect them, if heavy summer rainfalls are forecasted – I just place a transparent plastic cover against the house wall, not looking beautiful, but helpful.

Others are planted under a deciduous tree, which also protects the plants from heavy rainfalls in summer and gives them the sunlight they need in spring. This under-tree-planting is not good for autumn-flowerers, because the falling leaves in autumn do not look fine and can destroy the flowers when falling en masse.

Crocus growing in the open are sometimes destroyed by heavy rainfalls, but after some days the next flowers are coming up, so I don't mind loosing them until I have space and money (and time) to build an alpinehouse.

Otto, are you sure Pasche still has boulosii?

[Boyed]

Also one thing that I would like to note.
I think one of the most important things for best results is planting crocuses earlier in autumn (in September), even spring-flowering species and cultivars. As I noticed it is quite healthy for crocuses. The ones planted earlier considerably increase their rate of propagation, are larger and flower more abundantly.

And the another very important thing that I do - I plant all the new obtained ones in quarantine for the first year to observe them carefully against virus mosaic, which is very common. Then, after clearing the stock I place them with the main collection. It is a good way to decrease the level of virus spreading.

[Guff]

Just an idea, which I know would take alot of time and effort. 

How about a list of crocus that cross to each other.
Crocus that are pollen fertile and which are not.
Crocus that set seed and the ones that don't.

It would be great if you could look at a list and see what works and what doesn't. Or is there a book on the market that has the above info listed?

[Andrew]

This is my crocus collection.



As you can see, all pot grown. New corms go in clay pots, offsets/backups are in the plastic pots.

After they have finished growing they are all stored in garage conditions, completely dry but not baked including CC. vallicola, gargaricus and banaticus.

[Maggi Young]

A reminder that  all Crocus Pages  can be reached  from this  page :
 http://www.srgc.org.uk/genera/index.php?log=crocus  where many have been updated and there are  many extra lists etc.