Dry air at elevation and watering under cover
Last lesson was hard water and the vinegar fix. Today's the other half of that same problem, and honestly it's the one people notice even less.
Here's what actually happens up here. We sit around 4,600 feet, the air is dry most of the year, and when you put a cover over your bed, you'd think you're protecting the soil moisture. Sometimes you are. But a cold frame or a hooped row cover in full sun can pull moisture out of that soil faster than an open bed, because you've built a little greenhouse and greenhouses cook off water on the surface even when the air inside feels humid. Meanwhile an uncovered bed in our dry air just straight up dries from the top down, no drama, no warning, and you don't notice until the plants tell you.
So you end up with two different watering problems depending on what you're growing under, and most people water the same way regardless. That's the mistake.
Covered beds: check before you assume
If you've got a cold frame or hoops with plastic sheeting sealed up tight, check the soil before you water it, every time. Stick a finger in two inches down. If it's damp, leave it. I know that sounds basic, but people see condensation on the inside of the glass or the plastic and assume the bed's plenty wet. That condensation is coming off the soil and the plants breathing it out. It doesn't mean the root zone has what it needs.
Once a week, minimum, actually check. In our dry air a sealed cold frame can still dry out in four or five days on a sunny stretch, because remember, you're venting it (you'd better be, we covered that already), and every time you crack the lid you're letting dry outside air in and moist air out.
Row-covered beds: different animal
Fabric row cover breathes. It's not sealed like glass or plastic, so it doesn't trap humidity the same way, but it does cut wind and slow evaporation some. The soil under a row cover generally holds moisture a bit better than bare, open ground in our dry air. Not dramatically. Enough that you can usually stretch your watering interval a little compared to an uncovered bed of the same crop.
That's not permission to ignore it. Same rule: check before you water. Lift the cover, feel the soil, don't guess.
Watering under cover without wrecking things
A few practical points:
- Water in the morning if you can. Cold, wet soil overnight in a sealed frame is asking for the same rot and mildew problems we've talked about with poor venting. Morning water gives the day's heat a chance to work it in and dry the surface a touch before evening.
- Don't blast it. A watering can with a rose head, or a gentle drip line, beats a hose on full pressure. You're usually working in a tight space under a lid or hoops, and a hard stream splashes soil onto leaves and can knock over seedlings you just uncovered carefully (we spent a whole lesson on not wrecking seedlings, let's not undo it here).
- Watch the edges. The corners and edges of a cold frame dry out faster than the center, especially the side that gets more direct sun. I check corners first, every time, because that's where I get burned.
- If you're on drip line under cover, remember the vinegar lesson. Hard water clogs emitters whether they're inside a frame or out in the open bed. Covered beds just hide the problem longer because you're not looking at that section every day the way you might an open row.
The one I don't talk about much
One October I ran row covers over a bed of lettuce and spinach and kept harvesting into the first week of November, right when everybody I knew had already called it done for the year. I didn't make a big deal out of it at the time. I didn't post pictures or tell the ward group chat. I just liked knowing, quietly, that I'd stretched the season past where most people stop trying. That's most of what this whole course is, honestly. Small extra weeks nobody's watching you collect.
What made that bed work wasn't some clever trick. It was checking the soil by hand instead of trusting my eyes, and watering only when it actually needed it instead of on a schedule. Dry air will fool you either direction. It'll make a bed look fine when it's not, and it'll make you think you need to water more than you do because the air itself feels so dry against your skin. Trust the soil, not the air.
My opinion, for what it's worth: hard water and dry air are the two things nobody warns you about when they hand you a seed packet and a frost date. Everybody talks about temperature. Almost nobody talks about what our specific water and our specific air do to a garden once you've put a cover over it. Plan for both, and you'll save yourself a couple of bad surprises.
Before next time: go check whatever you've got covered right now, hoops or frame, and actually feel the soil at the center and at one corner. See if they're telling you the same story or a different one.