Seed Starting Instructions

Seed-starting mix is fine-textured, lightweight, and sterile — designed to allow delicate roots to penetrate easily and to prevent damping-off (a fungal condition that kills seedlings at the soil line). Standard potting mix is too coarse and too dense for small seedlings. Garden soil taken from beds is too heavy, may carry disease, and compacts in containers.

Fill trays to within 1/4 inch of the top. Moisten the mix before sowing — dry seed-starting mix is hydrophobic at first and needs to be thoroughly wet before seeds go in. A dry mix added to a tray and then watered from above tends to wash seeds into a corner.

Do not add fertilizer at this stage. Seed-starting mixes have little to no fertility by design — seedlings do not need nutrients for the first 2 weeks, and excessive nutrients at this stage can burn seedlings.

A general rule: sow seeds at a depth equal to 2–3 times their diameter. Very small seeds (lettuce, basil, celery) are surface-sown or barely covered. Medium seeds (tomatoes, peppers, brassicas) go about 1/4 inch deep. Large seeds (cucurbits, beans) go 1/2 inch to 1 inch deep — though cucurbits are typically better direct-sown.

For most crops, sow 2 seeds per cell and thin to 1 seedling after germination. This wastes some seed but ensures you have a plant in every cell. Keep the stronger seedling; remove the weaker by snipping at soil level with scissors (pulling can disturb the roots of the seedling you are keeping).

Cover seeds with dry seed-starting mix or vermiculite, which holds moisture evenly without crusting over.

Germination is primarily a function of soil temperature, not air temperature. Many warm-season crops require warmer soil temperatures than a typical house can provide in winter or early spring:

- **Tomatoes:** Optimum germination at 70–80°F soil. Acceptable range: 60–85°F. - **Peppers:** Optimum 80–85°F soil. Below 65°F, germination slows dramatically or fails. This is why peppers are notoriously slow to start in a cool room. - **Eggplant:** 80–90°F optimal. - **Cucumbers, melons, squash:** 75–85°F. These are typically direct-sown but occasionally started indoors in short-season zones. - **Lettuce, spinach, brassicas:** 45–75°F — cool-season crops germinate better in cooler conditions. Do not use a heat mat for these.

A seedling heat mat raises tray temperature 10–20°F above room temperature. Use a thermometer in the tray to confirm actual soil temperature. Once seeds germinate and sprouts emerge, remove from the heat mat — most seedlings grow best at 60–70°F air temperature after germination.

Light is the most common limiting factor in indoor seed starting. A south-facing window in most homes delivers insufficient light in January and February when most seeds are started — especially for crops like tomatoes and peppers that need high light intensity for compact, strong growth.

Seedlings that do not get enough light become "leggy" — they stretch toward the light source, producing tall, weak stems with large spacing between leaves. Leggy seedlings transplant poorly and are more vulnerable to wind and pest damage.

**What works:** A T5 fluorescent grow bar or LED grow light positioned 2–4 inches above seedling tops, on a timer for 14–16 hours per day. As seedlings grow, raise the light to maintain the 2–4 inch gap. LED grow lights use less energy and produce less heat than fluorescent — both work well.

**What does not work (reliably):** A single south-facing window in a temperate climate, especially in winter. It can work in very bright, unobstructed exposures but fails more often than it succeeds.

Move seedlings into full outdoor sun gradually — see Step 6 on hardening off.

Watering from above with a strong stream can displace small seeds and damage fragile seedlings. Use a gentle spray bottle or a watering can with a rose head during early stages.

After germination, transition to bottom watering: set the tray in a shallow container of water and allow the mix to absorb moisture through the drainage holes over 20–30 minutes. Remove and allow to drain. This method: - Keeps moisture more consistent throughout the depth of the cell - Prevents overwatering the surface (which encourages fungal damping-off) - Encourages roots to grow downward toward the water source

Allow trays to dry slightly between waterings — seed-starting mix should feel damp but not wet. Consistently wet soil promotes root rot and fungal disease.

In Anderson, CA, heated interiors can be quite dry in winter. Check trays daily. A dome lid placed over trays helps retain moisture during germination; remove it after sprouts emerge to prevent fungal problems from reduced airflow.

Seed-starting mix contains little to no nutrition. Once seedlings have developed their first true leaves (the second set of leaves after the initial seed leaves/cotyledons), begin feeding with a dilute liquid fertilizer every 7–10 days.

Use half the recommended rate of a balanced liquid fertilizer (fish emulsion, liquid kelp, or a commercial seedling fertilizer). Full-strength fertilizer on small seedlings can cause nutrient burn.

If seedlings look yellow but are otherwise healthy, increase fertilizer application. Yellowing is the most common symptom of nitrogen deficiency in container-grown seedlings, which rapidly exhaust the limited nutrients in seed-starting mix.

If transplant time is still weeks away and seedlings are root-bound in their cells (roots coming out the bottom, growth stalling), move them to individual 4-inch pots. Use regular potting mix (not seed-starting mix) at this stage.

Pot up carefully — minimize root disturbance. Fill the new pot with moist potting mix, make a hole the size of the seedling's root ball, set the seedling in, and firm the soil around it. Water gently. Keep under grow lights and at room temperature.

For tomatoes specifically: you can bury the stem deep during potting up — tomatoes root along buried stem, producing a stronger root system. Bury up to 2/3 of the stem, leaving only the top cluster of leaves above soil.

"Hardening off" is the process of acclimating indoor-grown seedlings to outdoor conditions — direct sun, wind, temperature swings, and reduced humidity — before planting them permanently in the garden. Skipping this step often results in sunburn (pale or white bleached patches on leaves), windburn, or transplant shock.

**Two-week hardening schedule:**

- **Days 1–3:** Set seedlings outdoors in a shaded, sheltered location for 1–2 hours midday. Bring them back in. - **Days 4–6:** Increase to 3–4 hours in partial shade. - **Days 7–9:** Move to a location with morning sun and afternoon shade for 4–6 hours. - **Days 10–12:** Full sun for increasing periods. Watch for wilting — bring in or water if plants look stressed. - **Days 13–14:** Leave outdoors overnight if temperatures stay above 50°F (for warm-season crops) or above 35–40°F (for cold-hardy transplants like brassicas).

**In Anderson, CA:** Hardening off in April and May requires attention to sudden heat. If temperatures spike above 95°F during the hardening period, skip outdoor time that day or limit to early morning only.

In Anderson, CA Zone 9b:

- **Tomatoes:** Transplant late March to mid-April. Soil should be above 60°F. Set plants out in the morning on a calm, overcast day if possible. Avoid transplanting before predicted heat spikes. - **Peppers:** Transplant late April to early May. Peppers need warmer soil than tomatoes — wait until soil is above 65°F consistently. - **Brassicas:** Spring crop, transplant mid-February to early March. These tolerate frost — a light frost after transplanting is acceptable. - **Lettuce:** Transplant February (spring) or August–September (fall). Summer transplanting is not recommended in Anderson — heat will destroy transplants.

Water transplants in with a dilute starter fertilizer solution (fish emulsion or compost tea) to reduce transplant shock. Install drip emitters immediately — do not rely on hand-watering newly transplanted seedlings through their first week in summer conditions.