 The structure of the root system , comprising a vertical tap root and multiple horizontal laterals , develops in the seedling 's first year . Thereafter , the sinker and laterals continue to lengthen , and new laterals appear . There are only three to five laterals at first , but this number typically increases to eight to ten within ten years . During the first winter , there is a great deal of root system development , especially elongation of the sinker root , but almost no shoot growth . By summer , the sinker root has generally almost reached the water table , and shoot growth increases substantially . Around February , the shoot forms a resting bud , and growth then ceases until October . On resumption of shoot growth , the shoots grow rapidly for a short time , while the plant is under little water stress ; then , with the onset of water stress , the plants settles into a long period of slower shoot growth . This pattern of summer @-@ only shoot growth is maintained throughout the life of the plant , except that in mature plants , seasonal shoot growth may cease with the formation of a terminal inflorescence rather than a resting bud . Inflorescence development continues after shoot growth ceases , and flowering commences in February or March . March and April are the peak months for flowering , which ends in July or August . 
