What Equipment Do I Actually Need to Start Seeds Indoors?
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To start seeds indoors successfully, you need five things: seed-starting trays or cells, seed-starting mix (not regular potting soil), a light source strong enough to prevent leggy seedlings (usually a dedicated grow light), a heat mat for warm-season crops, and labels so you know what you planted.
Everything else — humidity domes, spray bottles, seedling heat cables, propagation shelving — is genuinely useful but optional.
This guide breaks down each piece of equipment, explains what it does and why it matters, and gives you honest guidance on budget versus premium options so you can start growing without overspending.
The 5 Core Items Every Indoor Seed Starter Needs
Before getting into detail, here's the essential list:
| Equipment | Budget Option | Premium Option | Skip It? |
|---|---|---|---|
| Seed trays / cells | 6-cell or 72-cell nursery packs | Modular plug trays | No — required |
| Seed-starting mix | Bagged commercial brand (~$8–12) | Custom peat/perlite blend | No — required |
| Grow light | LED shop light (T8 full spectrum) | Dedicated horticulture LED panel | Rarely — only if you have perfect south window |
| Heat mat | Basic seedling heat mat ($20–30) | Thermostat-controlled mat | Depends on crop |
| Labels | Wooden popsicle sticks | Waterproof plant tags | No — always label |
Everything below explains how to use each of these well.
Seed Trays and Cell Containers: Size and Type Guide
Cell size matters.
The volume of a cell determines how long a seedling can stay in it before becoming root-bound.
Different crops have different space requirements:
• Small cells (72-cell or 128-cell trays): Ideal for crops that germinate quickly and are transplanted while still small — lettuce, spinach, basil, herbs. Also good for crops where you're starting many at once.
• Medium cells (50-cell or 32-cell trays): The most versatile size. Good for tomatoes, peppers, broccoli, and most standard vegetable crops.
• Large cells or individual pots (4-inch containers): Best for crops that grow large quickly and dislike root restriction — cucumbers, squash, and melons.
Reusable vs. disposable trays:
Rigid plastic cell trays (usually sold as 6-packs by nurseries) can be reused for several years if cleaned and sanitized between uses. Peat pots and coco coir pots are designed to be planted directly into the soil (eliminating transplant shock), but they are single-use and more expensive per seedling.
Biodegradable options are useful for crops sensitive to root disturbance, like melons.
Bottom tray (watering tray):
Always use a solid-bottomed tray beneath your cells.
Bottom watering — filling the bottom tray with water and letting the mix absorb it upward — is much better for seedlings than overhead watering, which can wash seeds out, compact the surface, and spread fungal spores.
The Cornell Cooperative Extension recommends that containers used for seed starting be sanitized with a 10% bleach solution
(1 part bleach to 9 parts water)
before reuse to prevent pathogen carryover [Cornell Cooperative Extension, 2023].
Seed-Starting Mix: Why It Matters More Than You Think
Seed-starting mix is not optional.
Using potting soil or garden soil in seed-starting trays is one of the most common causes of poor germination and seedling loss — due to coarse texture, weed seed content, and the risk of damping-off disease.
A good seed-starting mix is:
• Fine-textured and uniform — easy for tiny radicles to penetrate
• Pasteurized — free of weed seeds and damping-off pathogens
• Low in nutrients — seedlings don't need fertilizer until their first true leaves appear
• Well-draining but moisture-retentive — perlite or vermiculite provide this balance
For a full explanation of why seed-starting mix differs from potting soil, see our complete guide:
What is the difference between seed-starting mix and regular potting soil?
Grow Lights: Spectrum, Intensity, and How Long to Run Them
This is where most beginner indoor seed starters underinvest — and it's the single most common cause of leggy, weak seedlings.
Why a Window Isn't Usually Enough
A south-facing window in winter provides dramatically less light than most people realize. Even on a clear day, a window 1 meter from plants delivers only a fraction of outdoor light intensity — and in northern latitudes in January–March, clear sunny days are infrequent.
Without adequate light, seedlings stretch toward the light source (etiolation), producing long, weak stems and pale leaves. These seedlings are difficult to transplant successfully and susceptible to disease. The University of Minnesota Extension notes that light intensity — not just duration — is the primary limiting factor for indoor seed starting in most home environments [University of Minnesota Extension, 2023].
Light Spectrum: What Plants Actually Need
Plants use two primary wavelengths for growth:
• Blue light (400–500 nm): Drives vegetative growth — leaf development, compact internodes, thick stems. This is what you want during the seedling stage.
• Red light (620–700 nm): Drives flowering and fruiting. Not the priority for seedlings.
Full-spectrum LED grow lights
provide both blue and red wavelengths, plus the green middle spectrum that supports overall plant health. Modern full-spectrum LED grow lights are the most energy-efficient and effective option for home use.
Light Intensity: PPFD Basics
PPFD (Photosynthetic Photon Flux Density) measures the amount of usable light reaching a plant surface, in micromoles per square meter per second (μmol/m²/s).
• Seedlings and germination: 100–200 μmol/m²/s at canopy level is sufficient.
• Established vegetative seedlings: 200–400 μmol/m²/s.
• Most grow lights designed for home use : fall in the 100–400 PPFD range at 30–60 cm (12–24 inches) above plants, which is appropriate for seedling use.
Budget Grow Light Options
T8 LED shop lights (the 4-foot fluorescent-style fixtures, now widely available in LED) are an excellent budget option for seed starting. A 4-foot, 2-tube LED shop light provides adequate light for a standard 1020 seedling tray. Position it 5–10 cm (2–4 inches) above the seedling tops and raise it as plants grow.
Dedicated horticulture LED panels
(brands like Mars Hydro, Spider Farmer, Viparspectra) offer more precisely controlled spectrums and higher PPFD values, useful if you're growing into larger plants or need to cover more space.
How Long to Run Grow Lights
Run grow lights for 14–16 hours per day for seedlings.
Use a simple outlet timer to automate this — consistency is important.
Most plants need a dark period, so avoid running lights 24 hours.
Heat Mats: Why Bottom Heat Transforms Germination
Bottom heat — warming the growing medium from below — is one of the most impactful investments a seed starter can make for warm-season crops.
How Heat Mats Work
A seedling heat mat is a thin, waterproof electric mat placed under trays. Standard models raise the growing medium temperature to approximately 10–15°F (5–8°C) above ambient room temperature. In a 65°F (18°C) room, a mat brings the root zone to approximately 75–80°F (24–27°C).
Why Soil Temperature Matters for Germination
Warm-season crops (tomatoes, peppers, eggplant, basil, cucumbers) evolved in warm climates and require warm soil for reliable germination. Their seed enzymes become active only within a temperature range:
• Tomatoes: Germinate most reliably at 21–27°C (70–80°F). At 18°C (65°F), germination rate drops significantly and takes longer.
• Peppers: Require 24–32°C (75–90°F) for reliable germination — one of the warmest requirements of any common vegetable.
• Cucumbers and melons: Prefer 21–35°C (70–95°F).
• Cold-season crops (lettuce, spinach, broccoli): Do not need a heat mat; they germinate readily at 10–18°C (50–65°F).
A thermostat-controlled heat mat (with a probe placed in the growing medium) is the premium option — it cycles the mat on and off to maintain a set temperature rather than running continuously.
After Germination: Remove the Heat Mat
Once seeds have germinated and seedlings emerge, most do not benefit from continued bottom heat.
In fact, excess heat can dry out the growing medium too quickly.
Remove the heat mat once germination is complete (or move the mat to a new tray of ungerminated seeds) and
allow seedlings to grow at normal room temperature with good light.
Labels: Simple, Essential, Often Forgotten
Label every tray, every cell, every pot. It seems obvious until week three when you have eight trays of seedlings that all look like green specks and you genuinely cannot remember which row is the Sungold tomatoes versus the Black Krim.
What to include on your label:
• Variety name (not just "tomato" — "Cherokee Purple Tomato")
• Seed source or year (optional but useful)
• Date sown
Budget options:
Popsicle sticks or cut sections of mini blinds (white vinyl strips from old horizontal blinds are durable, waterproof, and free).
Write with a pencil — pencil labels last longer than many permanent markers, which fade in UV light.
Premium options: Commercially made plant tags in UV-resistant plastic, embossed aluminum labels, or simple waterproof label makers.
Useful Add-Ons Worth Considering
These are genuinely useful but not required for your first season of indoor seed starting:
Humidity dome / clear lid: A clear plastic dome over seedling trays maintains high humidity during germination, reducing moisture loss before seeds emerge. Remove once seeds are up, as high humidity after germination promotes damping-off.
Spray bottle or fine mister: For surface-watering very small seeds (like basil or lettuce) without displacing them.
For most watering, bottom watering via the tray is preferable.
Oscillating fan (small): Running a gentle fan on seedlings for 1–2 hours per day strengthens stems through mechanical stimulation (a process called thigmomorphogenesis). This helps produce stocky transplants that handle outdoor wind better. It also improves air circulation and reduces damping-off risk.
Propagation shelving: A metal wire shelving unit with grow lights mounted under each shelf allows you to start many more trays per square foot of floor space. Highly recommended if you grow large quantities of seedlings.
Budget vs. Premium: What's Worth Spending On
Not all seed-starting equipment is worth the premium price:
Spend more on:
• Grow lights — the difference between a $30 shop light and a $150 quality LED panel is measurable in seedling quality. If space is limited, invest in light.
• Heat mat with thermostat — for peppers especially, temperature accuracy matters.
Save money on:
• Trays — generic nursery cell packs work as well as branded options.
• Labels — popsicle sticks are fully adequate.
• Spray bottles — any fine-mist bottle works.
Don't buy:
• Expensive "seedling boosters" or "germination sprays" — these have little to no evidence behind them.
Proper light, heat, and moisture are the only germination factors that matter.
Quick Reference Equipment List
Must-have (beginner setup):
• [ ] 72-cell or 50-cell seedling tray with bottom watering tray
• [ ] Quality seed-starting mix
• [ ] Full-spectrum LED grow light (T8 shop light minimum)
• [ ] Seedling heat mat (for tomatoes, peppers, basil)
• [ ] Plant labels
Worthwhile additions:
• [ ] Humidity dome / clear lid for trays
• [ ] Outlet timer for grow lights
• [ ] Small oscillating fan
• [ ] Thermostat controller for heat mat
Skip:
• Germination boosters and sprays
• Expensive branded trays and containers
• Any product marketed primarily for appearance rather than function
Frequently Asked Questions
Q: Can I use a regular fluorescent shop light instead of a grow light?
A: Old T12 fluorescent tubes are much less efficient than modern full-spectrum LED T8 tubes, but they can work for basic seed starting at close range (5–10 cm above plants). However, if you're replacing or buying new, LED is the clear choice: more light output, less electricity, no mercury, and last significantly longer.
Q: How far should grow lights be from seedlings?
A: For T8 LED shop lights, position them 5–10 cm (2–4 inches) above the seedling tops. For dedicated horticulture LED panels, follow the manufacturer's recommendations for PPFD at distance — typically 30–60 cm (12–24 inches). Keep lights on a chain or adjustable mount so you can raise them as seedlings grow.
Q: Do I need a humidity dome for all seeds?
A: No. Humidity domes are most useful for seeds that take longer to germinate (peppers, parsley, celery) — the dome prevents the surface of the mix from drying out before seeds emerge. Fast germinators like radishes, lettuce, or squash are unlikely to need one. Always remove the dome once seedlings emerge to allow air circulation.
Q: How many grow lights do I need for a 1020 standard seedling tray?
A: One 4-foot, 2-tube T8 LED shop light positioned 5–10 cm above the tray provides adequate light for most seedling crops.
For peppers and tomatoes grown past the seedling stage indoors, you may benefit from higher PPFD from a dedicated horticulture panel.
Q: Can I reuse old soil from last year's pots to fill seed-starting cells?
A: No — old potting soil should not be used in seed-starting cells.
It may harbor damping-off pathogens from previous plants, has depleted nutrient levels, and often becomes compacted and hydrophobic after a season. Always use fresh, sterile seed-starting mix for germination
References
1. University of Minnesota Extension. (2023). Starting Seeds Indoors.
2. Cornell Cooperative Extension. (2023). Seed Starting for the Home Gardener.
3. University of Illinois Extension. (2023). Vegetable Garden Planning.
4. Royal Horticultural Society. (2024). Sowing Seeds Indoors.
5. USDA Natural Resources Conservation Service. Soil Health and Plant Propagation.
About the Author: [Author Name] is a home gardening educator and indoor growing specialist with [X] years of experience starting seeds indoors across multiple climate zones. They contribute to the Reencle blog on practical gardening, seed starting, and sustainable growing methods. [Author credentials here.]
Related Posts:
• When should I start seeds indoors before the last frost? A month-by-month seed-starting calendar
• What is the difference between seed-starting mix and regular potting soil?
• Can I use homemade compost directly in seed-starting trays, or is it too strong?
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