Steiner talked about four year rhythm on peppers etc and it's a persistent rumour. I was told it was to do with Mars but didn't have chapter and verse.
I found a link now.
"And now let me tell you something. You all know of the existence of the grubs of cockchafers. These little worm-like creatures are particularly harmful when they eat up our potatoes. There are years when the potatoes are unharmed by these troublesome little maggots, and then there are years when simply nothing can be done because the grubs are everywhere at work. Well now, suppose there has been a year when the grubs have eaten nearly all the potatoes — if you wait now for four years, the cockchafers will be there in great numbers, because it takes them four years to develop from the grubs. There is a period of approximately four years between the appearance of the grubs — which, like all insects, first have a maggot form before becoming a chrysalis — and the fully developed insect. The grub needs four years to develop into the cockchafer. Naturally, there are always cockchafers, but if there are only a few grubs some year, four years after that there will only be a few cockchafers. The number of cockchafers depends upon the number of grubs that were present four years earlier.
We can see quite clearly that this period of time is connected with the rotation of Mars. The course of propagation of certain insects shows us the kind of influence that Mars exercises upon the life of the earth. But the influence is rather hidden. The influence of the sun is quite obvious, that of the moon not obvious to the same extent, and the influence of Mars is hidden. Everything for which intervals of years are needed on the earth — as in the case of grubs and cockchafers — is dependent upon Mars. So there you see a significant effect of Mars."