Common Seed Starting Issues - And How To Avoid Them!

We’ve all been there – a plant you’re particularly looking forward to seeing spring up just hasn’t, well, sprung. As with most worthwhile endeavors, planting seeds has the potential for heartbreak and this is especially true for indoor seed-starting. This artificial environment can cause stresses and problems rarely seen in the outdoor garden.

Now that many of your seeds may have sprouted already, here are four common indoor seed-starting diseases (and pests!) to watch out for, and what to do about them.

Before jumping in, it may be worth a quick recap of conditions needed for seeds to emerge and thrive in 7 Easy Step to Starting Seeds Indoors.

1. DAMPING OFF.   Damping off is by far the most common disease issue in an indoor seed-starting setup. Caused by a fungus, its hallmark symptom is a narrowing of the plant at the base—until it looks like floss—followed within about twelve hours by the collapse and death of the seedling.

Its main cause? Poor air circulation.

In our experience, it is possible to experience damping off at nearly any temperature between 55 and 85 degrees—so the problem can't be solved simply by heating up or cooling down the environment. The key to avoiding the disease is providing adequate airflow: leave indoor seedlings open to the larger room rather than enclosing them in any way, and if using a cold frame, provide adequate ventilation as temperatures permit.

Avoid overwatering at all costs! Once your seeds have germinated, their water needs decrease dramatically. While a nice, soaking wet flat can look attractive with its bright green sprouts against the dark soil, it is also a perfect environment for damping off. Of course, we are imperfect gardeners and we make mistakes, so if you find that you've accidentally soaked a flat, immediately set up a small fan to dry out the top half-inch of potting soil. If the surface is dry, damping off is very unlikely. (Watering from beneath is one way to achieve this, too. Also: note that seedlings grown in a well-ventilated cold frame are much less prone to damping off than seedlings grown in a room with basically still air, so it's worth experimenting with a cold frame if you never have before.)

2. LEGGINESS. Often those seedlings most prone to damping off (above) are seedlings that we'd also call "leggy"—stretched-out, pale, easily toppled seedlings that often open their cotyledons waaaay higher than they should. Legginess is the top problem of gardeners who start their seedlings on their windowsills. It is rare that a windowsill, even south-facing, can provide enough intense, direct sunlight to make for healthy seedlings. The result is young plants that stretch window-ward in search of more intense rays. The solution is either to provide artificial light for your indoor seedlings or to move your seed-starting setup to a protected location outdoors, either a cold frame or greenhouse. Providing light is usually the easiest solution, but just know that when we say provide light, we mean PROVIDE LIGHT. Drop that shop light fixture to within 1-2 inches of the soil at first, and then gradually elevate it so that it is never more than 1-2 inches from the top of the tallest leaves.

Already have leggy seedlings? Immediately do whatever you can to provide them with stronger light without exposing them to unprotected outdoor conditions. Leggy seedlings can sometimes be rescued but will be knocked down and likely killed if moved outside without some serious hardening off. If your seedlings are still young, it's usually wiser just to pull them and resow in a stronger-light environment.

4. APHIDS.   Last but not least, an uncommon but occasional pest of the indoor seed-starting set-up is the aphid. Aphids are pests of houseplants and often make their way into the home on green materials bought at commercial greenhouses in winter. They are easy to deal with—a spray of soapy water is usually all it takes to dispense with them—but if they reach your seedlings at a very young age they can make waste of them quite quickly. The good news is that if you have not had an aphid problem with your houseplants, you almost definitely will not see aphids on your seedlings.