Starting seedlings indoors, whether it’s vegetables, annuals, or perennial ornamentals, offers lots of benefits. You get a head start on the growing season, you have much better control over temperature and moisture, and there are no critters eating your seeds. But transitioning seedlings from an indoor location to the outdoors can be challenging. This article walks you through the process of successfully transplanting your seedlings.
Harden Off the Seedlings
No matter how strong and healthy your seedlings look, the first indispensable step is to harden them off because outdoor conditions are very different from a sheltered indoor environment. Outdoors, the seedlings need to withstand temperature fluctuations between day and night, wind, strong direct sunlight, and heavy rain. When seedlings are abruptly exposed to these conditions, they can suffer damage and fail to thrive. Instead, about 7 to 14 days prior to transplanting, the seedlings should be gradually exposed to cooler temperatures and outdoor light, starting with a few hours for the first couple of days and slowly increasing the time outdoors. For details, follow step-by-step instructions for hardening off plants, which can also be done in a cold frame.
Time It Right
There is no cutoff date for transplanting seedlings after the hardening off period. If the seedlings look weak and spindly, it is not likely they will do better after transplanting. Leave them in pots for a few more days until they grow healthier and stronger.
When they look ready, pick a relatively cool, cloudy day for transplanting. Avoid hot, sunny days, as this will stress the seedlings.
Prepare the Soil
Seedlings have tender, fragile root systems that cannot push through heavy compacted soil. You might have to prepare the soil before transplanting. Amend dense clay soil with organic matter.
The soil needs to be well-drained. Avoid planting right after a heavy rain when the soil is soggy and wet. Working wet soil causes it to compact and dry hard like a brick, choking young, tender roots.
Plant the Seedlings
Planting methods differ depending on the type of seedlings you are working with. Some, like tomato seedlings, benefit from a deep planting hole while strawberries, for instance, prefer a more shallow hole with their roots feathered out across the soil. Seedlings grown from bulbs require different depths while annuals and perennials do well with a planting hole that is twice as wide and as deep as the pot. With the exception of roses and a few other ornamentals grown on rootstock, the top of the root ball should be covered with soil. Roots of all transplants should be completely covered.
Before planting the seedlings, water them well. When removing the seedlings from their pots, handle them as gently as possible. Do not pull them out of the pot but carefully slide the root ball out of the pot by turning the pot upside down. Gently hold the stem between your fingers and squeeze the bottom of the pot until it releases the root ball. If the seedling is root-bound and won’t budge, don’t try to pry it but cut the container open down the sides with a utility knife instead.
Backfill the planting holes with topsoil and gently tap down the soil around the roots.
Provide Additional Protection
Even seedlings that have been properly hardened off can suffer a certain amount of transplant shock. A tall paper or plastic cup with the bottom removed, or short sections of 4- to 6-inch PVC pipe work well to protect seedlings from too much sunlight during the first few days.
Wind can be equally damaging to the stems of young seedlings. For support, insert a wooden barbecue skewer in the soil next to the stem and loosely tie it with a piece of cotton string (for tall seedlings, two ties at different levels might be needed).
For vines such as zucchini or squash, place a couple of rocks around the base which prevents them from getting knocked over and breaking in the wind.
You can protect young plants from succumbing to insect and animal damage by installing floating row covers or wire cages.
Watering immediately after planting helps minimize transplant shock. Water gently using a watering can with a rose or a hose with a spray nozzle and be careful not to wash away the soil or knock over the seedlings. Water is a must even when the soil seems moist. This settles the soil around the roots and removes air pockets.
Watering gently at soil level directs water to the roots and helps avoid leaf and stem damage and fungal disease. Use a spray nozzle with a mist or sprinkle setting. While most plants benefit from drip irrigation, it isn't practical for everyone. If you need to water overhead, do so early in the morning to allow your seedlings to dry out before nighttime temperatures drop.