Cherry tomatoes are a popular choice for home gardeners due to their abundant yields and relative ease of care. Achieving a successful harvest depends entirely on precise timing, as these plants are highly sensitive to cold. Successful timing requires calculating two distinct dates based on local climate conditions: the start of indoor growth and the final outdoor planting date.
The Indoor Head Start: Timing Seed Germination
The first step involves counting backward from the anticipated date of the last spring frost. This timing allows seedlings to develop into robust transplants ready for the garden. For most cherry tomato varieties, the ideal time to sow seeds indoors is six to eight weeks before the planned outdoor transplant date.
Starting seeds too early results in weak or leggy plants that struggle outside, while starting too late shortens the growing season. Seeds should be planted about a quarter-inch deep in a sterile seed-starting mix, maintaining the soil temperature between 75°F and 85°F for optimal germination. Once seedlings emerge, they require 14 to 16 hours of light daily, often supplied by grow lights, to prevent stretching and weakening of the stems.
Identifying the Safe Transplant Date
The most important factor for transplanting cherry tomatoes outdoors is the consistent warmth of both the air and the soil. Tomatoes are warm-season plants that suffer damage or die if exposed to temperatures below 40°F to 50°F. The threshold for planting is determined by the average last expected spring frost date and the soil temperature.
Gardeners should locate their local average last frost date using regional resources. It is recommended to wait until at least two weeks past this date to ensure the risk of a late cold snap has passed. Even if the air temperature seems warm, the soil must be consistently warm enough to support root growth.
Cherry tomato plants require a soil temperature of at least 60°F, measured four inches below the surface, before they can be safely transplanted. Planting into colder soil will cause the young plants to “sulk,” resulting in slow root development and difficulty absorbing nutrients. The soil typically reaches this temperature when daytime air temperatures are reliably in the 60s and overnight temperatures stay above 50°F.
Preparing Plants for the Outdoors
Once the safe transplant date approaches, seedlings must undergo “hardening off.” This is a gradual acclimatization to harsher outdoor elements, including direct sunlight, temperature fluctuations, and wind. Seedlings grown indoors are accustomed to a sheltered environment and will suffer severe sunscald or transplant shock if moved directly outside.
The hardening off process should begin seven to fourteen days before the target transplant date. Start by placing the plants in a protected, shady location outdoors for one to two hours on the first day, ensuring there is little wind. Each subsequent day, gradually increase the duration of time spent outside and slowly expose the plants to filtered sunlight, eventually moving toward direct sun.
During this period, reduce both the amount of water and fertilizer the plants receive. This intentional stress slows growth and encourages the development of a thicker stem and a more robust root system. After a week to ten days, the plants should be able to remain outside day and night, provided the nighttime temperatures are consistently above 50°F.