March 20 is the first day of spring, but Southern California gardeners can start planting their spring garden early in the month as warmer weather and longer days take over.

Prepare the soil in raised garden pots: The success of vegetables grown in raised boxes has as much to do with the soil as it does with almost anything else. Look for soil mixes made specifically for pots, usually a mix of compost and peat rich in organic nutrients. Since compaction is always a problem with pots, the soil should be light to allow easy drainage of the water. Consider lining the bottom of the pots with gardening cloth so that the roots of the plants do not reach the underlying soil.

Fertilize everything: Most plants grow best in the spring, so feeding them now will yield long-term results. An all-purpose fertilizer should contain nitrogen to promote healthy leaf growth, phosphorus to develop roots, stems, and flowers, and potassium to help plants absorb nutrients. Feed avocados, citrus, fruit, and roses with a well-balanced fertilizer specifically designed for each type of tree. For fruit and rose trees, wait until the first sign of new leaves before fertilizing.

Maximize fruit production: Apple, apricot, peach, and plum trees typically produce more fruit than trees can ripen. As the fruit begins to appear, twist the extra fruit when it reaches the size of a marble. Leave two of the largest, healthiest young fruits on every 12 inches of stem.

Plant shrubs: For a quick pop of color in shady areas, plant blooming azaleas, leaving the root ball an inch higher than the ground. Azaleas have long-lasting flowers and do well in the shade. Try planting native shrubs like calendula, a yellow-flowered shrub that blooms in winter and spring, and Cleveland sage, which produces silver-green leaves and purple flowers in spring and summer.

Plant vegetables and herbs from seed: After the last chance of frost (around the middle of the month) and the soil warms up, cultivate your garden soil about a foot. Add organic soil planting amendments. Plant warm season vegetable seeds, including tomatoes, bell peppers, green beans, cucumbers, squash, eggplants, onions, potatoes, spinach, turnips, and corn. It is also the time to plant herbs from seeds like basil, mint, oregano, parsley, and rosemary. You can still plant cool-season vegetables, such as broccoli, lettuce, cabbage, and kale. Good crops that can be planted now and throughout the year are carrots, beets, and radishes.

Deadhead’s Spent Flowers: Perennials that have flowered in winter may need to be groomed. Remove fallen or dried flower heads. If necessary, cut the stems. This trimming will force the plants to redirect their energy into new growth for the spring.

Add mulch: Mulch becomes natural compost in the soil over time. Add two to three inches of new mulch around the garden. The new mulch will continue what the mulch does best: retain moisture, reduce soil erosion, and help prevent weed growth.