Maryland Grows

Let’s talk more about seed-starting! Last month I posted about how to get your house ready for a seed-starting project: picking a space to use, deciding where to hang your lights, and choosing the lights. I also wrote a bit about what containers to use, but in this post I’ll give you more detail, and also talk about what “soil” (actually soilless mix or growing medium) to use.

Containers

There are basically two parts to a seed-starting apparatus: the tray, and the pot or cell. Here’s some information about each.

Trays

• The purpose of a tray is to contain or capture water. You need a tray unless you want a big mess. It should not have holes in it.
• Trays can be any size larger than a pot. Standard industry size is 10”x20”. You can also use takeout containers (or any food-grade plastic), old baking pans, or anything else that suits your needs.
• Most trays are plastic (aside from the baking pans). Standard trays full of pots sometimes crack when lugged around and left outside, so consider doubling them up or buying the heavy-duty ones.

Pots

• The purpose of a pot is to contain the medium in which a plant grows. Pots are separate entities, and cells are connected pots. You can buy cell sets that fit standard trays. You can also save the cells and pots that you bought plants in. Yogurt cups and the like are great to recycle into pots, or you can use plastic drinking cups. Plastic egg cartons can substitute for the smallest size of cell set.
• Pots must have drainage. If water can’t drain out of a pot, plant roots can rot. Commercial pots will have holes already; if you use recycled items, punch holes with a nail or a knife or whatever you have (the shape doesn’t matter, but make several).
• If you don’t want to buy plastic, you can spend more and get pots or cell sets made of silicone or ceramic. These should last many, many years and be easy to clean.
• Any pot of the above types needs to be cleaned before each use. A 10% bleach solution is effective at killing pathogens that may lurk in bits of leftover soil. You can instead use dish soap if you’re pretty sure the pots haven’t been exposed to plant diseases.
• The other type of pot/cell set on the market is the plantable kind. These are made of compressed peat, coir, or processed manure (they don’t smell!). They are filled with growing medium just like a plastic pot, but the whole thing can be put in the ground when the plant is ready.
• Make very sure to keep plantable pots moist at all times, starting by soaking them before using and continuing until planting time. Remove any dry rims and some of the bottom before planting. Dryness can prevent proper plant growth.
• Plantable pellets (made of peat or coir) expand when moistened and have a hole to put a seed into. They can also be planted whole, or transplanted into a bigger pot.
• How big a pot to choose? It depends on how many times you want to “up-pot” or transplant into a larger container. If you start with small cells, the seedlings will have to be moved into larger pots, maybe more than once, but you are saving space, soil, and water in the early stages. (Just be sure you have room under lights for your expanded plant kingdom!) Planting directly into larger pots means you won’t have to up-pot, but you may waste time, space and materials if seeds don’t germinate, and it’s harder to keep the soil watered.

Growing Medium

It’s recommended to start seeds in a soilless mix consisting mostly of peat or some other organic material. There are lots of choices available on the market, and if you’re ambitious, you can mix your own. Read HGIC’s page on the topic and check out Jon Traunfeld’s post on peat-free mixes.

For smaller seeds, you want to find a finer-cut mix (lightweight and fluffy, not heavy like sand); larger seeds can tolerate a mix with larger particles. The name on the package may not mean much: “seed-starting mixes” can be quite rough in texture, and “potting mixes” vary a lot too. Look at the ingredients and try to avoid anything with “forest products,” which seems to mean little bits of wood.

Seeds themselves contain nutrients to get a baby plant started, so germination and early growth don’t require fertilizer in the growing medium. If you’re going to be growing the plant in that medium for more than a week or so, though, the mix should have fertilizer or compost in it. Alternatively, you can add fertilizer when you water. Or you can add your own compost to your growing mix, as long as it’s finished and screened, but don’t use garden soil, which may contain pathogens or weed seeds.

Next month I’ll take you through choosing what seeds to start, how to get them to germinate, and how to care for your young seedlings.

In the meanwhile, here are some more items you might consider acquiring into addition to the seeds themselves:

• A seedling heat mat, especially if you are planning to start seeds for summer vegetables and flowers. Seeds need warmth to germinate, and sometimes a bit of extra heat helps.
• A sprayer (for getting the soil surface wet without washing tiny seeds away) and a watering can with a narrow spout.
• Clear plastic domes that fit over your trays. These help keep moisture in when seeds are germinating and plants getting started. You can buy them or improvise them out of recycled plastic clamshells (like for salad mixes).
• Labels!!!

I’ll tell you more about all these helpful items next month.

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.