A seed starting medium that contained fertilizer? That's creative!! Generally, seed starting soils are pretty bare bones - that's because the seeds just need an anchorage and even moisture source. Everything else they need to grow is contained internally. Additional fertilizer/"plant food" is unnecessary (and sometimes harmful) until they grow on and develop their second set of true leaves and get potted up into regular potting soil.

Seedling stretch is most often associated with insufficient light levels and I'd guess that's what may be causing yours. There is nothing to do to fix it other than intensify the light source or move it closer. Pinching more mature plants, depending on type, may help to encourage bushiness.

Thanks gardengal! I did a little research and it seems that too much nitrogen can make pansies stretch. I guess I was just wondering what effect seedling stretch has on the plant. Will it still flower? I can find very little information about it, but my seedlings are looking pretty spindly.

Are your seedlings all together in one container? Or planted individually into cells?

If they've reached a size where they have true leaves you can probably gently take them from their first home and move them on to the next size up of container.

In that container you'll need a mix that is coarse and sharp so the little plants have to grow excellent roots to gather their food and water. They won't start out looking hugely lush above ground but, once you've got a generous root system going they can take weekly feeding.

Be prepared to pot on more than once so the plants aren't checked in their growth. It doesn't take pansies long before they're sending roots out the drainage holes. At the first sight of a white tip - move them along into the next pot size up until they're the size you want to plant out. Keep nipping off any flower buds up to then.

After your first move - give them shelter from wind, excellent light but not direct full sunlight, and a gradual introduction to the great outdoors over one to two weeks. Protect from the usual munchers. Water from the bottom until the top is damp but not awash and let the pots drain well after you have. Good air circulation around the plants, without draughts or screaming gales, is important to prevent fungal attacks.

When you have warmer weather in early May, ensure they don't dry out, and start regular feeding using a foliar mix at the recommended rate. You're aiming for compact plants with good dark green leaves. Big floppy things are an open invitation to hungry invertebrates.

If you add your compost about now to the site where they'll be flowering then, in about a month, it should be ready to keep your youngsters moving along, and supplied with food/moisture as they flower. Adding it when you actually plant is usually too late to be effective.