April is the pivot month for the medicinal herb garden. Everything that was dormant is waking up, the ground is becoming workable in most temperate climates, and the decisions you make in the next few weeks will determine the abundance and quality of your harvest through summer and into autumn. It is one of the most rewarding and most productive times of the year in the medicinal garden, and also one of the most time-sensitive.
What to Do First
Before anything else, observe. Walk the beds and note what has survived the winter, what is emerging strongly, what looks stressed or depleted, and what has not returned at all. Perennial herbs like valerian, echinacea, motherwort, and lemon balm will be pushing up new growth. Woody herbs like thyme, rosemary, and sage will be showing fresh new growth at their tips. Note what needs division, what needs cutting back, and where there is space for new plants.
Dividing Established Perennials
Early spring, while perennial herbs are just beginning to grow, is the best time to divide clumps that have become congested. Lemon balm, yarrow, echinacea, valerian, and comfrey all benefit from being divided every two to three years. Dig the whole clump, divide it into sections each with healthy roots and new growth, replant the divisions, and water in well. This both rejuvenates the original plant and gives you new plants for expanding the garden or sharing.
Sowing and Planting Out
April is the month to direct-sow calendula, borage, and (in milder climates) chamomile. In most temperate climates, it is still too cold for tender herbs like basil and tulsi outside, though these can go into a propagator or warm windowsill indoors. Pot-grown plants of lavender, thyme, and rosemary can be planted out once the risk of heavy frost has passed in your area.
Feeding and Mulching
A light top-dressing of well-rotted compost around perennial herbs in spring gives them the mineral base they need for the growing season. Medicinal herbs in general benefit from leaner conditions than vegetables, but they do need some nutrition, and compost is preferable to synthetic fertilizer because it supports the soil life that helps roots access what they need.
The Herbalist Codex app has individual growing notes for all the herbs you are likely to be working with this month, including their specific soil preferences, companion planting suggestions, and the best time to start harvesting each as the season develops.