From a plants perspective, several forces are combining this month to tell them what to do . . . or what not to do. Foremost, days are growing longer and your plants are getting two more minutes of daylight every day. Along the coast, daytime temperatures are two degrees warmer than last month and soil temperatures are almost two degrees higher as well. These are the unbendable signals from nature that tell your plants when to grow, flower, set seed, drop leaves or go dormant. Unfortunately, your plants are rather indifferent to your personal wishes for flowers or growth or about anything else. Different groups of plants respond quite differently to exactly the same signals. As you learn how different plants in your garden are pre-programmed to respond to these forces you will struggle less and enjoy your garden more.
During April many “cool-season” annual flowers, vegetables and herbs are putting forth their final glorious burst of bloom before time runs out on them. Pansies, violas, primrose, snapdragons, stock, sweet peas and most poppies are in bloom. However, the longer days are taking their toll on cabbage, kale, broccoli, cauliflower, lettuce and arugula, telling them to hurry up and flower. Not a great time to plant “cool-season” annuals.
For another group of plants, the “warm-season” annuals, the lengthening days and warming temperatures make this their best planting month. Now is the time to add these to your garden. They include petunias, dahlias, verbena, lobelia, zinnias, impatiens, begonia and coleus. Edibles planted now include tomatoes, peppers, squash, beans, eggplant, and cucumber. April is the first month to tuck in a few varieties of culinary basils, including sweet, lemon and cinnamon basil.
Fertilizing is essential to these “warm-season” plants, as they burst forth with new leaves, buds, blooms and fruits. The heaviest, almost glutinous feeders in our gardens are roses, citrus, fruit trees, clematis, fuchsias and hydrangeas. Feed them all. Azaleas, camellias, gardenias and most ferns should prefer an acid fertilizer; cottonseed meal works especially well in sandy or clay coastal soils. Gardenias and citrus need additional iron and this is the time to give them a good dose. Iron won’t work when applied to the cool soils of winter, but it will now.
Most other plants also need nutrition now and this is one of your most important chores this month. A notable exception however, is our California native plants. These are generally “cool season” plants, growing and flowering in a perfect concert to our winter wet and summer dry Mediterranean climate. Do not fertilize or plant California native plants during spring or summer.
For most plants in the ground we recommend blends of organic fertilizers, rather than liquid, water-soluble or synthetics. Organic based fertilizers contribute to a healthy living soil and gently release their nutrients over a long period. Organic nutrients also contribute less to groundwater pollution, coastal runoff and nitrification of our wetlands like Upper Newport Bay, the Bolsa Chica Wetlands, the San Joaquin Freshwater Marsh and Aliso Creek. We’ll discuss lots more about how healthy soil means healthy plants in future columns.
Roses are displaying their biggest and best blooms of the year. Don’t worry too much about a few aphids, just hose them off. But do pay attention to the first signs of diseases like powdery mildew or rust. Rather than reach for the chemicals we usually suggest exchanging susceptible varieties for those with better disease resistance. Cultural adjustments, such as improved the air circulation around the plant will improve the situation dramatically.
This may be the best month of the year for planting avocadoes, blueberries, citrus, clematis, wisteria and turfgrass. Thin the nickel-sized fruit of peaches, nectarines and apricots to one every 4-6 inches. Do not prune hydrangeas now or you will be without flowers all summer. Stake tall perennials like delphinium, foxglove, lilies and dahlias to prevent breakage. Apply a fresh two to three inch layer of organic mulch over exposed soil between trees, shrubs and perennials.
Especially in April, take your gloves off for a moment, stand back and enjoy the marvels of nature in your garden. It doesn’t get much better than this.
Ron Vanderhoff is the Nursery Manager at Roger’s Gardens, Corona del Mar.