What is a Plant Plug? A Beginner’s Guide

If you start a seedling and let it grow in a single cell or container filled with potting soil, you have a plant plug. With plant plugs, you can start growing vegetables, herbs, flowers, and other plants right away in an easy and inexpensive way.

What Exactly is a Plug?

A plug is a seedling that is grown in its own cell or container instead of being planted in the ground or a larger pot that is shared by many plants. The plug is made up of the plant and the soil around its roots that are inside the cell.

Plug trays typically contain many interconnected cells, allowing you to start a large number of seedlings together in a small space. The individual cells provide each seedling with enough room for its roots to establish during the initial growth period.

The plugs can be moved to larger containers or straight into garden beds once they have strong root systems and some leaves. When you use plugs, you don’t have to plant seeds directly in the garden and wait for them to germinate. It helps the plants grow faster before they are moved to their permanent spot.

Benefits of Using Plugs

There are several advantages to using plugs rather than sowing seeds directly

• Earlier harvesting – Plugs get a head start on growth indoors or in a greenhouse, allowing earlier transplanting and harvesting of crops.

• Higher germination rates—Seeds are more likely to grow when they are in the perfect, controlled conditions that plug trays offer.

• Less wasted seeds – With direct sowing, many seeds fail to germinate or seedlings die off. Plugs allow you to first establish strong seedlings before putting them in the ground.

• Easier spacing – Plugs can be precisely spaced when transplanted, while seeds may germinate too close together or leave gaps.

• Less weeding – Established plugs are better able to outcompete weeds after transplanting.

• Wider variety – Plugs enable you to grow many more varieties in a small space compared to direct sowing.

• Convenience – Plugs are clean and easy to handle compared to loose seeds.

How to Grow Plugs Successfully

Follow these tips for the best results when growing plant plugs:

• Select Plug Trays – Plug trays come in many different cell sizes and configurations. Smaller cells like those holding 1-2 inch plugs are good for starting seeds. Larger 3-4 inch plugs give transplants more room to develop before planting. Look for trays with drainage holes in the bottom of each cell. Self-watering trays that provide water from below are excellent for maintaining consistent moisture.

• Use a Seed Starting Mix – Plug trays require a lightweight, well-draining seed starting mix. These mixes are soilless, containing peat moss, vermiculite or perlite. Do not use regular potting soil which can compact and get waterlogged. Moisten the starting mix before filling cells, then plant 1-2 seeds per cell and cover lightly with mix.

• Provide Warmth for Germination – Seeds need sufficient warmth to germinate, usually 65-75°F. Use a heat mat under the plug tray or keep it in a warm greenhouse. Once sprouted, move to an area with temperatures around 60-70°F to avoid leggy growth. Provide ample light from grow lights or indirect sunlight.

• Maintain Even Moisture – Check plugs daily and water when the starting mix begins to dry out on top. Water gently to avoid dislodging seeds. Uneven moisture causes seeds to rot or seedlings to damp off. Self-watering trays prevent drying out but avoid overwatering. Allow good drainage.

• Wait to Fertilize – Seedlings in plugs get nutrients from the starting mix and stored energy in the seed itself. Avoid fertilizing until the first true leaves emerge. Then use a diluted liquid fertilizer like fish emulsion once a week. Excess nutrients can damage tender young plants.

• Harden Off Before Transplanting – A week before transplanting plugs outside, begin the hardening off process. This transitions the plants from indoor to outdoor conditions. Set them in a sheltered spot outdoors for a few hours, gradually increasing time over the week. Protect from direct sun and wind which can shock tender plants. Avoid transplanting before the last spring frost date.

• Transplant Carefully – When transplanting plugs, handle them gently by the leaves or root ball, not the stem. Make holes the same depth as the plug. Gently loosen and spread out any roots that have escaped the plug before placing it in the hole. Firm the soil around the base without compacting it and water well. Keep newly planted plugs well-watered until established.

Ideal Plants for Plug Growing

While almost any garden plant can be started as a plug, some types are especially well-suited:

• Vegetable transplants – tomatoes, peppers, broccoli, cabbage, lettuce

• Herbs – basil, thyme, oregano, mint, cilantro

• Flowers – marigolds, zinnias, cosmos, snapdragons, petunias

• Fruits – strawberries, blueberries, raspberries, blackberries

The convenience of plugs makes them a great way to add a variety of plants to both flower and vegetable gardens. Follow proper growing methods for thriving transplants that establish quickly after planting.