If you are growing warm-season crops—such as basil, tomatoes, or peppers—from seed indoors during cold winter months, you must warm their soil. Ultimately, your goal is to get as many seeds to germinate as quickly as possible. For crops that need warmer soil temperatures, especially when you’re starting them indoors during colder months, a seedling heat mat can speed up the germination process and ensure success.

Heat mats, which are placed directly under your seed tray, can warm soil to an average of 15 to 20 degrees Fahrenheit above room temperature. Be sure to use a heat mat specifically designed for seed germination. Seedling heat mats are insulated and moisture-resistant, so you can place them on normal surfaces under your seed trays.

Gardening Under Lights Book

While many succulents can't be grown long term indoors, due to a lack of light, there are some species that can tolerate indoor growing without grow lights. When you're gardening under lights indoors, it's good to know which plants can tolerate lower light conditions.

Haworthia are one type of succulent that can tolerate lower lighting, and can be maintained in a bright windowsill. Haworthia are compact succulents that grow in a whorl of foliage. Their shallow root systems make them perfect for keeping in small pots as easy-care houseplants.

Gardening Under Lights Book

A smaller two- to four-lamp fluorescent fixture can sit just a few inches above young seedlings. As plants grow larger, move the fixture a foot or so higher. Large fluorescent fixtures may need to be 2 to 3 feet above plants to avoid causing heat stress.

I use a large adjustable shelf with 4-lamp T5 fixtures to start seeds, grow microgreens, transition transplants. You might find large fixtures like these can get pretty warm so you may not need a seedling heat mat, or you can remove one or two bulbs to reduce light and heat load if it seems your young seedlings need a bit less of either.

Gardening Under Lights Book

Plants have varying requirements for how, where, and when to take cuttings, the ideal size of the cuttings, and how long they may take to root. Some plants, such as succulents, will root from the base of a leaf. Others, like begonias and African violets, will root straight from the leaf surface.

Many perennials are propagated by taking root cuttings or divisions. You can propagate certain tropicals, such as pothos ivy, by setting a stem in water for a few weeks.

Gardening Under Lights Book

Calabrese and broccoli are cool-season crops, and temperature controls flowering responses; most do not handle heat well. Flower heads can also be malformed or damaged if young transplants sit at temperatures below 40°F (4°C) for a few weeks.

The ideal temperature range for happy broccoli is between 65°F and 80°F (18–26°C). This can be tough to maintain in an enclosed grow room or grow tent unless it is air-conditioned, but normal household temperatures might be adequate.

New BOOK! Gardening Under Lights: The Complete Guide for Indoor Growers

Not technically a disease, rather a physical disorder related to water and humidity management and types of light, oedema blisters can cause defoliation.

Oedema occurs when roots take up water faster that the plant can use it. Once water pressure builds up enough in the plant cells, they burst, leaving visible blisters.

Gardening Under Lights Book

Before you make your selection of which type of pot to use, think about whether you want to reuse the container. A reusable container will be more stable and permanent, but biodegradable seed plugs allow you to plant the entire cell directly into a larger pot or your garden without lifting out the seedling or disturbing its root system.

These biodegradable seed starting cells can be planted directly into a larger container, or into the garden, once the seedling's roots reach the bottom and edges of the plug cell.

Gardening Under Lights Book

Having the right spectrum of light is not enough to grow healthy plants. You also need the right quantity to fuel photosynthesis.

While accurately measuring light for plant growth might seem complicated—and the fi ne details are beyond the scope of this book—an introductory understanding of how to measure and manipulate light will help take your indoor-growing skills to an entirely new level.

Gardening Under Lights Book