April is a transitional time for the garden, shifting from winter planning to active growing. This month presents a unique duality: conditions are cold enough for certain crops to thrive, yet warm enough to begin preparation for summer harvests. Successful April planting requires two main activities: sowing seeds directly into the garden for cool-season vegetables and starting the seeds of heat-loving plants indoors. The timing depends on your local climate zone and the unpredictable nature of spring weather.
Understanding April’s Variable Conditions
Planting decisions in April are governed by two environmental factors: the average date of the last frost and the soil temperature. The average last frost date is the historical point after which the probability of a freeze drops significantly, but a gardener must still be prepared for unseasonable cold snaps. For many cool-season crops, the soil needs to be workable and thawed, not necessarily warm.
A soil thermometer can confirm that the ground has reached the minimum temperature required for germination. Hardy seeds, such as those for leafy greens, can germinate in soil temperatures as low as 40 to 45 degrees Fahrenheit. This is significantly cooler than the 60 to 65 degrees required for the germination of summer vegetables. Paying attention to these metrics ensures seeds do not rot in overly cold, wet soil.
Cool-Season Crops for Direct Sowing Outdoors
April is the ideal time for direct sowing seeds of vegetables that prefer cool spring temperatures and mature quickly. Root crops should be planted directly where they will grow, as they do not tolerate transplanting well. Carrots require a finely tilled seedbed and should be sown shallowly, about one-quarter inch deep, and later thinned to prevent tangled roots.
Radishes are an excellent choice for April, germinating quickly and maturing in as little as three to four weeks. They should be planted about a half-inch deep, often interspersed with slower-growing crops like carrots to mark the rows. Beets can also be sown directly; each seed cluster, or glomerule, may produce multiple seedlings that require thinning to achieve proper spacing.
Leafy greens thrive in spring conditions, as the cool air prevents them from bolting, which is the premature production of a flower stalk. Spinach and arugula seeds should be planted a quarter-inch deep, and the resulting plants can withstand light frost. To ensure a continuous harvest, a technique called succession planting involves sowing a small batch of seeds every two to three weeks until the weather becomes consistently warm.
Transplanting Hardened Seedlings
Certain cool-season vegetables benefit from being started indoors several weeks earlier to gain a head start, making them ready for transplanting in April. This group primarily consists of the Brassica family, which includes broccoli, cabbage, and cauliflower. These plants require a long, cool growing period to produce large, flavorful heads.
Before moving these seedlings permanently into the garden, they must undergo a process known as “hardening off.” This gradual acclimation involves moving the young plants outdoors for increasing periods each day over a period of five to seven days. This process toughens the plant tissue, preparing it for the sun, wind, and temperature fluctuations of the outdoor environment.
Seedlings are ready to be planted when they are about three to six inches tall and have developed their second set of true leaves. When transplanting, bury the stem slightly deeper than it was in its pot and water immediately to settle the soil around the roots. Hardy herbs like parsley and cilantro, often started indoors in late winter, can also be transplanted out after hardening off.
Starting Heat-Loving Vegetables Indoors
Although the focus in April is on planting cool-season crops outside, it is also the time to begin the indoor preparation for the summer garden. Plants that require a long, warm growing season, such as tomatoes, peppers, and eggplant, must be started from seed indoors now to ensure they are mature enough to transplant after the last frost. These varieties need six to eight weeks of indoor growth before they are ready for the garden.
These warm-season seedlings require specific indoor conditions to thrive, including a temperature maintained around 70 degrees Fahrenheit for optimal growth. They also need significant light exposure, often requiring 14 to 20 hours daily of full-spectrum light from a grow lamp to prevent them from becoming leggy and weak. Providing these controlled conditions in April ensures the plants develop a robust root system and strong stems, ready for the garden in late May or early June.