Humidity Promotes Early Root Growth

In the early days of your plant's development, humidity is key. Whether it's seeds or clones, you want a high level of humidity and temperatures between 70 and 90 degrees Fahrenheit to promote rapid root growth.
To keep humidity high, cover your seeds or clones with a humidity dome or tent. These items will trap the moisture you've applied to your grow media or seedling trays, creating a micro-climate that is extremely damp.
Heat mats can aid in maintaining optimal temperatures if you're growing in a space that averages 60-75 degrees Fahrenheit. If you're in a space with higher temperatures on average, such as a greenhouse, be cognizant of how hot your space gets because a heat mat may increase temperatures to the point that they become harmful.
Be sure to remove your dome or covering and reduce humidity once your plant has sprouted to avoid damping off or rotting. While near-100% humidity levels are great for developing roots, sprouts can quickly bite the dust if they are overly moist.