Young Pecan Tree
Pecans: Northern vs Southern
The answers lie in the way our native pecan trees are adapted to different parts of their native range. Pecans grow wild from central Mexico in the south to Iowa in the north. There are pecans that can ripen nuts in southern Ontario Canada with the lake effect heat there. Trees growing at the northern reaches of the native range are adapted to the winter cold and the length of the summer season. Trees growing further south do not need to be adapted to the northern winter and get a long hot summer to ripen their nuts.
Northern varieties have been selected or bred to ripen their nuts by or before the first hard freeze each year. Southern varieties have been selected or bred to fit the conditions of a longer season with more heat and humidity. Southern trees do not need as many hours of winter chill before the break buds and begin to grow in spring. This can be a major problem in northern areas where a late winter warm spell can cause them to break dormancy before it is safe from frost. Likewise, southern varieties may need more frost free days to ripen their nuts than are available.
Northern varieties are adapted to the deeper cold and require more hours of cold before they break dormancy in spring. They also ripen their nuts earlier, before the first killing freeze of a northern winter.
Rootstocks, why are they important? In the south, Elliot pecans are used to grow rootstocks for grafted varieties. Elliot is a wonderful disease resistant pecan of excellent quality. As a rootstock, is is vigorous and fast growing. It is a low chill variety so, in the south it breaks bud early and pushes the tree to grow for a long season. When taken north, it does the same thing. It tends to push early and will push even northern varieties to break buds early, often too early and the buds can be damaged by frost.. Elliot is not adapted to a cold climate and can suffer from severe winter injury when temperature fall to sub zero levels.Sometimes Elliot is killed by the cold and when the rootstock dies, so does the rest of the tree.
In northern areas, rootstocks are usually grown from known cold hardy vigorous variety seed. Native seedlings can make good rootstocks but they can have variable growth habits. The varieties Giles, Colby and Kanza make good cold hardy rootstocks. Other northern varieties can be used as well.
As we have seen, Southern rootstocks cannot go north but, can northern rootstocks go south? As a matter of fact, they can. Northern rootstocks grow just fine in the south. The leaf out a few days later than the southern trees which has a small impact on the overall speed the tree grows compared to southern stocks. But, as the trees mature, things begin to even out and mature trees yield the same as those on southern rootstocks.
Pecan trees can live far north of where they will ever ripen a nut. So, where can pecans be grown and expect to make a crop? Ripening pecans is all about heat. Especially warm nights. Summer heat is measured by cooling degree days (the formula is ((max temp + min temp)/2) – 65 Fahrenheit). Pecan trees need at least 950 cooling degree days to ripen nuts. This information can be found through the weather service or possibly through your State Agriculture Extension Service.
Pecan trees also need at least 180 days without a killing freeze of 28 degrees to ripen a crop of nuts. Outside the native range, growing pecans is all about micro climate conditions. There are die hard pecan growers who live in just the right conditions and have chosen the right varieties who make pecans where they shouldn’t make but they are the exception to the rule.
The answers to the question can they be grown where I live, is specific to where you live and what your goals are. Pecans should be grown everywhere they can be and they can be grown a lot more places than they are now grown.
Perhaps this helps clarify Pecans: Northern vs Southern in a way that is helpful.
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