Two common mistakes are planting seed too early and starting with too large of transplants. It is believed starting seed early or using large transplants will lead to an earlier harvest. But doing so often backfires and seedlings are killed or stunted and harvest can be delayed with yields reduced.
Vegetables are divided into cool and warm season crops. Cool season vegetables like lettuce, radish, peas, potatoes, onions, cabbage and broccoli are tolerant of and need cooler soil and air temperatures.
Warm season vegetables like tomatoes, pepper, sweet corn, cucumbers, squash and melons require warmer soil temperatures for germination and root growth and these crops are not tolerant of frost.
When it comes to direct seeding or transplanting in the garden, cool season crops sensitive to heat while ripening are planted in April. Most warm season vegetables are planted in May in Nebraska.
To determine when to plant, monitor soil temperatures. Even if air temperatures are warm, soil temperatures may be colder than optimum. We are planting into soil and not into air.
Use a soil thermometer to test soil temperatures at about a two inch depth. You can also monitor general soil temperatures for Nebraska on the crop watch website at https://go.unl.edu/x5rm
For cool season vegetables, a minimum soil temperature of 40 to 45 degrees Fahrenheit is the general rule. For warm season crops, it is 50 to 60 degrees F. These are minimums. Optimum soil temperature for quick germination and steady growth is often warmer.
Also, the colder soil is the longer it takes seed to germinate so not many days are gained by seeding early. For example, at the minimum soil temperature of 45 degrees F, carrot seed can take 21 or more days to germinate. At the optimum temperature, they can germinate in seven days.
If warm season vegetables are planted too early and soil is too cold for germination or root growth, the seed may rot, seedlings damp off, or at the very least germination is delayed. If germination occurs, seedling growth may be stunted or seedlings, as well as transplants, could be killed by an April frost.
If cool season vegetables are seeded too late in spring, crops like peas, radish and broccoli will have poor quality if they ripen while temperatures are hot. Potatoes, onions and cabbage are more tolerant of hot temperatures while ripening and can be planted later than April if needed.
Know the vegetables and monitor soil temperature, then plant at the ideal time. If you wish to seed earlier, there are tricks to use to warm soil before seeding. These include laying down black plastic and the use of hot caps or water towers. These have to be put in place prior to not after seeding to warm soil first.
And here is why starting with larger transplants can lead to a later harvest. Vegetables that are best transplanted over direct seeding, like tomatoes, do best if transplants are a certain age or size. If too old or large, the transplant suffers greater transplant shock and growth is often stunted.
When buying transplants, look for short, stocky plants with healthy green foliage and leave the larger, more expensive ones for someone else to buy.
For questions on vegetable gardening, e-mail me at kfeehan2@unl.edu.