Can Dill and Fennel Cross Pollinate? No.

Dill (Anethum graveolens) and Fennel (Foeniculum vulgare) are often quoted as cross pollinating easily if planted close.  Many reputable gardening books and publications as well as seasoned home gardeners also claim that dill and fennel will hybridise and produce "less than desirable" offspring.  Do dill and fennel really cross pollinate with one another?  The answer may surprise you.

At first glance dill and fennel appear to be similar in appearance, so one may assume that they could cross.

There is a lot of anecdotal evidence that they do cross with each other.  Many reputable gardening books, online publications, as well as seed saver groups and organic gardening societies who claim that they cross easily.  Unfortunately they never show any pictures of these mysterious and supposedly common intergeneric hybrids.  I dislike gardening books as they are mostly written by people with little to no knowledge of gardening, as such they are often filled with inaccuracies.

Many home gardeners claim that dill and fennel cross easily.  The amount of nonsense ideas that are perpetuated by home gardeners who should know better is rather large and worrying.  Home gardeners also spout a lot of weird superstitions and counter-intuitive cultural taboos so it is not difficult to ignore their claims when they do not provide any proof.  I am yet to hear of any home gardener who saved seed from dill and had anything odd grow out of it, let alone anyone who has even attempted to grow it out for a few generations and try to stabilise it and create something great.  I have seen a few photos of fennel that has crossed with weedy feral fennel, and have the gardener claim that it is a cross with dill, but unfortunately it is not.

Dill and fennel are both members of Apiaceae (Umbelliferae) family, but they are not closely related.  They are from different genus and species.  Carrots, parsnip, coriander, skirret etc are all part of that family, all of them are from different genus, yet none of these will hybridise to produce intergeneric hybrids.

Sometimes different species do not cross, such as many Cucurbita species, sometimes different species cross easily, such Capsicum species, sometimes they can cross but not very easily and only with a great deal of intervention.  Intergeneric hybrids are reasonably uncommon, so one may assume that they would not cross, but some intergeneric hybrids in orchids or cacti are simple enough to achieve, so things get murky here.

There is no evidence in any peer reviewed journal, or anything written by any plant breeder anywhere in the world (that I can find) which claims that dill and fennel can cross.  There have been some attempts by universities to cross them using embryo rescue techniques etc to incorporate some of fennel's disease resistance into dill, but I am unable to find results of these attempts without paying for subscriptions to things I don't want to pay for.  Clearly they were not terribly successful as it is not possible to buy seeds of these plants.

If it were possible to cross dill and fennel people would do it.  Fennel is a true survivor (as can be seen on many roadsides across Australia), dill tastes great but is a bit weaker, a cross between them would be lovely.  The F1 plants would likely be dreadful, which is to be expected, after this they would begin to segregate into lines that are increasingly stable.  After careful selection, and perhaps a little back crossing to lock in desirable traits, it would not be long before these hybrids would be better than either original plants.  As no one appears to be doing this it is safe to assume that they do not cross as easily as all of those gardening books and seed saver groups and gardening societies say they will.

Both dill and fennel, like many herbs, change how they smell when they flower.  Often home gardeners confuse this for their plant somehow hybridising with something else.  Some herbs, such as coriander look different when they flower and many home gardeners will swear that it somehow crossed with dill, again this is not the case.

Wild, feral, weedy fennel is a rather common roadside weed in Australia and many other parts of the world.  It WILL cross with fennel from a great distance and the resultant plants are often of poor quality.  They do not look or smell overly like fennel and differ from the parent considerably.  The F1 fennel bulbs are greatly reduced and the smell is often odd and unpleasant.  None of this has anything to do with dill or any other plant, it is simply fennel crossing with fennel.

I have tried to track down seeds of these supposed dill/fennel hybrids, but no one has them.  I have also tried to cross dill and fennel myself many times, but have had no success, ever.  I have had success creating wide crosses with other plants in the past yet am unable to achieve this supposedly simple cross, so I am doubting that dill could hybridise with fennel.  Personally, I don't see how they could cross.  It is a rather wide cross to begin with, there would be many benefits from creating such a cross and breeding resistance and vigour into dill, yet no one (neither home breeders nor commercial plant breeders) seems to be attempting it successfully. 

When seed saving, Dill can and will easily cross pollinate with other varieties of dill.  Fennel can and will easily cross pollinate with other varieties of fennel.  They will not cross with one another.

As far as I can tell dill can not cross pollinate with fennel as I have seen absolutely no proof, but I am happy to be wrong about this!  If you believe that you have successfully (and/or accidentally) crossed dill and fennel, and you are absolutely certain that you saved seeds from dill, please send them to me and I will grow them out for a few years to try and put some of the hardiness of fennel into something that tastes like dill. 

I am only interested if dill was the female parent, if you collected seed from fennel I am not interested at all.  What you will most likely have is not just fennel, which I don't particularly like, but fennel that has crossed with poor quality weedy fennel, which I like even less.

Alternatively is you happen to know of some scientific peer reviewed paper (not just the web page of some seed saver group or a gardening book written by someone with no experience) that claims dill and fennel do cross easily I would love to read it.