Learn Spanish (Latin America): Mi abuelo sembraba muchas semillas en el huerto. - My grandfather used to sow many seeds in the vegetable garden.

The imperfect tense (sembraba) is used to talk about habitual or repeated actions in the past, which is why it translates to "used to sow." If you used the preterite (sembró), it would mean he sowed seeds on one specific, completed occasion.

Does the verb sembrar have a stem change here?

No. While sembrar has an e to ie stem change in the present tense (like él siembra), regular -ar and -er verbs never have stem changes in the imperfect tense. You simply take the infinitive stem sembr- and add the ending -aba.

What is the difference between an huerto and a jardín?

A jardín is typically a decorative garden with flowers, shrubs, or a lawn. Un huerto (or huerta) specifically refers to a vegetable garden, allotment, or small orchard where you cultivate things to eat.

How would I use this lesson's grammar to say "The more seeds he sowed, the more vegetables grew"?