Many of the present seedling groves are of uncertain origin and represent greatly varying values.  No doubt some of these groves are the progeny of especially selected trees known to have considerable merit.  On the other hand, it is very apparent that many of them are the result of a great demand for seedling trees when the industry was in its infancy twenty or thirty years ago.  At that time without doubt, great quantities of walnuts were planted without due regard for their parentage.  Again, there is a wide range of variability among the individual trees of any grove, as variations in type of tree, blooming season, character of foliage, resistance to disease, productivity and character of the nuts.

Type of Tree

The tree types vary from the upright, sturdy individual to the more or less spreading, weeping types which droop nearly to the ground under the burden of the crop.  The upright, vigorous growing type is well exemplified in the Eureka.  On the other hand, such varieties as the Prolific have a spreading, bushy habit and an almost semi-dwarfness characterizes their growth.

Blooming Season

It is not unusual to find the blooming season in an ordinary seedling grove extending over a period of from a month to six weeks.  A few individual trees leaf out and blossom with the first signs of spring.  Then the great majority of the trees in the grove come out in full leaf.  But there are frequently trees still leafless after the nuts on the early individuals are of the size of a marble.  This variation in the blooming season has considerable economic importance in relation to the harvesting and marketing of the nuts as well as the avoidance of diseases and frost which may be more prevalent during certain periods in the spring.

Foliage Characteristics

The character of the foliage varies from the broad-leaved types, whose foliage somewhat resembles that of the horse-chestnut, to the narrow-leaved varieties whose leaves have a tendency to curl up like the foliage of the Winesap apple.  The broad-leaved types are much more densely foliated and this factor has considerable bearing on the problems of sun-scald on the twigs and trunks of the tree and the exposure of the nuts to this injury.  For this reason, the densely foliated varieties may prove best adapted to the inland valleys, where the difficulties of sun-scald are most prevalent.  The more sparsely foliated types often appear to have less blight on the nuts and leaves because of their exposure to the sunshine.

Disease Resistance

Probably one of the most important limiting factors in walnut production in California, and especially in the older walnut sections, is the bacterial disease commonly known as walnut blight.  The inroads of this disease have caused a very heavy dropping of the nuts during many seasons of the past, and although a great deal of time and scientific effort has been devoted to the control of the trouble, there is no satisfactory known means for the prevention of walnut blight at the present time.