Beginners Guide to Seed Starting Trays for Gardening

Are you struggling with seedlings in your home garden? Finding it challenging to manage indoor seed starting? Seed starter trays have become essential tools for modern gardening enthusiasts, offering one of the simplest methods to begin growing vegetables, flowers, and other plants indoors before the warm season arrives. However, with the overwhelming variety of trays available—differing in size, function, and material—how do you determine which one best suits your needs? What are the key differences between them?

To be honest, I never used specialized seed starter trays in the past. My approach was more about "upcycling"—using various paper cups, old pots, yogurt containers, and egg cartons—anything that could hold soil! While these containers do work and can be a budget-friendly solution for gardeners, I found this makeshift method less than ideal.

The primary issue with this approach is the difficulty in management. Different containers require varying amounts of water to maintain moisture, they occupy more space, and when it's time to move seedlings outdoors, under grow lights, or to a new windowsill, you must handle each seedling individually. This becomes a tedious task.

So, are seed starter trays absolutely necessary for beginner gardeners? The answer is no—but they do make life much easier and significantly improve your success rate!

Seed starter trays simplify the seedling process by conveniently grouping plants into easy-to-manage units.

• Easier Lighting: When all seedlings are clustered together rather than scattered in various-sized containers, providing adequate light becomes simpler. Trays can be easily placed under grow lights and moved as a single unit.
• Simplified Watering: Uniform cell sizes make watering more consistent, meeting different seedlings' moisture needs. Additionally, proper drainage in trays helps prevent overwatering.
• Better Organization: Similar plant types can be grouped in separate trays—herbs in one, lettuce in another—making it easier to handle hardening off or transplanting when some seedlings require earlier attention than others.
• Humidity Control: Some trays come with transparent plastic covers or domes that help regulate humidity, particularly crucial during germination and early growth stages.

Seed starter trays are typically made from rigid reusable plastic or thin recyclable plastic designed for single use. Some combine plastic drip trays with biodegradable cells or peat pellets that can be planted directly into the garden.

The variety of designs can be overwhelming for new gardeners. Your choice ultimately depends on several factors. Below, we explore common designs to help determine which might work best for you.

Most seed trays measure approximately 10×20 inches, but the number of "cells"—individual planting units—varies significantly.

The more cells a tray has, the sooner seedlings will outgrow it and require transplanting into larger containers.

Trays range from 12 to 128 cells. Based on experience, trays with 24 to 48 cells work best, safely maintaining plants indoors for 4 to 8 weeks before transplanting becomes necessary.

• High-cell-count trays (with shorter indoor growing periods) work particularly well for lettuce varieties like spinach, kale, and arugula.
• Lower-cell-count trays (24-36 cells) are ideal for tomatoes, cucumbers, bell peppers, herbs, and squash.

Root vegetables should generally be sown directly in the garden rather than transplanted.

Visible roots emerging from cells or peat pellets indicate it's time to transplant seedlings to larger containers or the garden.

Your choice between styles ultimately comes down to personal preference.

Consider these accessories for indoor seed starting. They simplify the process and increase success rates. If choosing just one, LED grow lights should be your first upgrade!

• LED Grow Lights: Specially designed lights provide seedlings with appropriate light levels to prevent growth issues.
• Heating Mats: Maintain consistent soil warmth to accelerate and improve germination rates.
• Base Trays: Provide drainage for trays with holes and allow bottom watering, helping prevent disease and pest problems.
• Clear Dome Covers: Help retain heat and moisture in trays, particularly crucial during germination. An excellent low-cost investment when heating mats aren't available.

To determine which seed trays best meet our gardening needs, we tested three popular styles: biodegradable cell inserts on plastic base trays , peat pellet inserts with base trays , and rigid plastic cell trays with watering bases .

An excellent starter tray for beginners—just add water to expand the peat pellets. No additional potting soil or container filling required. Seeds germinated quickly, and the transparent humidity dome reduced watering needs. The drawback is that seedlings outgrow these pellets quickly, requiring prompt transplanting. Best suited for lettuce or plants that can be transplanted within one to two weeks after germination.

The larger peat pots provide ample growth space, allowing seedlings to thrive for 6 to 8 weeks. Ideal for tomatoes, peppers, cucumbers, or squash. The base tray facilitates watering, but care must be taken to avoid overwatering and mold. Separating the strips before planting made transplanting easier with less plant disturbance. An excellent, user-friendly tray for most plants.

This tray's reusability simply requires fresh potting soil for each use. Despite the high cell count, the 1.8-inch-deep plugs allow substantial root development. Seedlings grew well for 4-6 weeks before requiring transplanting. Ideal for herbs, peppers, lettuce, and similar plants. However, removing plugs during transplanting proved challenging, requiring careful loosening with a spoon or popsicle stick to avoid root damage.

Overall, all three tray styles demonstrated distinct advantages and disadvantages, making them suitable for different purposes. For all tested trays, planting 2-3 seeds per cell and thinning to one seedling after germination yielded the best results.

The small Jiffy peat pellets worked exceptionally well for lettuce, herbs, and brassicas that could be transplanted quickly, even in cooler weather. Tomatoes and cucumbers struggled in these pellets due to limited root space and the need for rapid transplanting.

The larger 32-cell peat pots excelled with plants requiring more establishment time before planting. Tomatoes, cucumbers, herbs, and squash thrived in these trays for up to 8 weeks. The only drawback was that some plants eventually overshadowed others, requiring separation and spacing.

The reusable 72-cell tray with 2-inch-deep plugs performed surprisingly well, even for larger plants like tomatoes and peppers. The deeper plugs allowed plants to remain in trays longer than expected. However, removing plugs without root damage proved somewhat challenging and required finesse.