Seed Starting Kits and Supplies – What You Actually Need
A boxed kit gets you a tray and a lid. The rest of the list is short, cheap and decides the outcome.
TL;DR
- Kit = tray + dome. Add mix, light, labels; heat mat only for warm-season crops.
- Judge a bundled light by stated wattage, not by the picture.
- Everything else is optional; drainage and light are not.
What a kit includes, and what it does not
The standard kit is a 10 by 20 inch tray with cells, a clear dome and a bottom tray. Sold at that level it is a container, not a system: it holds mix and humidity, and it drains if the base tray is used properly. What it does not include is the light — and light is the input that decides whether six weeks of growth produces a stocky plant or a pale stem leaning at the glass.
Kits that include coir pellets are convenient for germination and awkward after: a pellet holds little volume, so a tomato outgrows it in three weeks and needs potting on sooner than it would in a 72-cell tray. If you plan to keep seedlings indoors longer than a month, cells beat pellets.
The short list, in priority order
1. Seed starting mix. Light, sterile, free-draining. Not garden soil, not last year's potting compost. This is the one line item worth buying rather than improvising — the soil mix guide covers what is in it and a working home recipe.
2. A tray that drains. Holes in the base, and a bottom tray to catch what runs through. A tray without drainage is the fastest route to damping off.
3. Light. A cheap shop light or LED bar hung a few inches above the tray, on a timer for 14-16 hours. This is what prevents leggy seedlings, and it costs less than the kit.
4. Labels. Pencil on wood or plastic; marker fades.
5. Heat mat and dome. Optional, but the mat is what makes peppers and eggplant germinate in weeks rather than months. A thermostat is worth the extra few dollars — an uncontrolled mat cooks a tray left on.
What to skip
Heated propagators with built-in thermostats are a lot of money for a windowsill's worth of plants. Misting bottles are fine but a squeeze bottle or a jug is free. Soil test kits, rooting hormone and "seed starter" fertilizer are all things you may want later and do not need on day one — in fact feeding seedlings before they have true leaves does more harm than good, as the fertilizer guide explains.
Tools for this job
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Seed starting kit with tray and dome
Cells, cover and base in one box — the shape most windowsills fit.
Plant labels and pencil
The cheapest item on the list and the one you will miss most.
Related guides
Frequently asked questions
What is in a typical seed starting kit?
Most kits are a plastic tray with cells, a clear humidity dome and a lid or base tray — sometimes with compressed coir pellets. That is a starter set, not a complete one: it usually leaves out light, a heat mat and labels, which are the three things that decide whether the seedlings survive past three weeks.
Do I need a seed starting kit at all?
No. A tray with drainage holes plus a clear cover does the same job, and a clear plastic punnet from the supermarket is a free version of the dome. Buy the kit if you want the cell sizes and fit to be consistent between seasons; skip it if you are starting twenty plants once.
What supplies matter most?
In order: seed starting mix, a tray that drains, a light close enough to matter, and a way to water without disturbing the surface. Heat mats and humidity domes help germination but are optional; light is not.
Is a heat mat worth buying?
For peppers, eggplant and anything slow and warm-season, yes — it is the difference between two weeks and five. For tomatoes and most annuals, room temperature is enough. Buy the smallest one that fits your tray and put a thermostat on it.
What about seed labels?
Buy or make them. Six weeks after sowing nobody remembers which cell was which, and a tray of unlabelled seedlings is a tray you cannot plan around. A permanent marker on a plastic strip fades in sun; a pencil on a wooden stick does not.
Should I buy a kit with a grow light included?
Watch the light, not the tray. Kits that bundle a small light often ship a low-output one that must sit two inches from the leaves to work. If the light has no stated wattage or lumens, it is decoration.