Reconsider the Seed
Do you have years-old baggies and canisters of seeds lurking? Although they look dead, healthy seeds are ALIVE. They breathe, absorbing oxygen and releasing carbon dioxide. They ingest water from the air. They wait in dormancy -- each with embryo and stored food encased in a protective coat -- to swell and grow. Moisture, heat, and mechanical damage in storage take their toll over time though. So don't expect all saved seeds to sprout equally well.
Check Seed Viability
To check if veggie or flower seeds are viable, do a trial run. Wrap 20 seeds in a moist paper towel. Fold paper towel so seeds are completely enclosed. Put the wrapped seeds in a closed baggie in a warm place (70 to 80 degrees F) to germinate. After 3 days, open to see how many seeds have sprouted. Check again daily for a week or two. Vigorous seeds will sprout quickly. Count total sprouted seeds to get the germination rate. For example, if 10 sprout, that's 50 percent germination. Plant accordingly.
Start Cool-Weather Flowers and Veggies Indoors
Cool-weather calendula, aka pot marigold, can be started from seeds indoors now. Ditto for the slow-germinating celery and the bulb-forming onion. Celery germinates best at 60 to 70 degrees F; transplant when seedlings are 3 to 5 inches, before the taproot forms. Onion bulb growth depends on day length: the short, dark period makes the onion shape. Long-day onions produce a good-sized bulb in northern states; short-day varieties are better for southern states with longer summer nights.
Check Indoor Plants for Critters
Seemingly overnight, colonies of aphids erupted on my decorative ivies and favorite marjoram plant! Aphids suck plant sap from tender stem tips and new leaves. First line of defense: spray plants hard with water to dislodge the pests. Aphids still clung to the fuzzy marjoram leaves, so I clipped away about 4 inches of infested stems and leaves. Hoping to induce a fatal chill, I put the plant outdoors for two cold (not freezing) days and nights. If the aphids persist, I'll prune away even more.
Use Insecticide Judiciously
By now, plants brought indoors last fall are likely stressed from insufficient light, house temperature, over- or underwatering, and incompatible humidity. So their natural defenses are depleted, not unlike our susceptibility to winter colds, flu, allergies. Aphids, downy and powdery mildew (fungi), and whiteflies can easily infest a stressed plant. When water spray and insecticidal soap don't eliminate a plant pest, the biodegradable insecticide Neem is a viable, effective remedy. Used as directed, one or two Neem applications will likely kill the pest with no measurable toxic effect on mammals and beneficial insects.