At the Edge of the Orchard by Tracy Chevalier

At the Edge of the Orchard  begins in the mid-1800s with a family struggling to survive in the black swamp area of Ohio. Although the family is fictional, Tracy Chevalier surrounds them with history of that time period. To stake a claim of 100 acres, a family was required to grow 50 apple trees and 20 peach tress within three years. John Chapman (also known as Johnny Appleseed) sold seeds and saplings to the settlers, travelling by boat to the Ohio swamp areas. Seeds were plentiful from cider makers who discarded them and were sold fairly inexpensively, but saplings were more costly for the settlers, making it difficult for them to establish trees in the required time. Along with fighting the bogs to make the ground arable, families also had to contend with sickness that came with the damp areas and mostly carried by mosquitoes.
After a tragedy, the story follows the eldest son, Robert, to the Gold Rush of California where he meets Cornishman William Lobb a plant collector (I'd heard about William Lobb and his brother sometime ago and also mentioned them in Gwinnel Gardens, part of the Lowenna series)  They had carried many plants and seeds from across the world to be established in English gardens. Preparing and shipping plants from America was no easy task as they had to be taken from the ship's hold out to sunlight every other day and watered for several months. Some of the plants were contained in a Wardian case providing a small greenhouse to protect the plants. William Lobb collected and shipped both Redwoods and Giant Sequoias to England.

We sometimes forget how difficult it was for American pioneers, trying to survive and protect their children from ailments for which there was no cure. Travelling across the country was difficult and many chose instead to travel by boat down the east coast of the Americas, around the southern tip, Cape Horn, and then north along the west coast to get to California.