The general impression is that cold-frame operation ends with June and the setting out of all early plants. Far from it!
So many are the uses of the cold frame through the summer that there is always more space for all that could be done. Seeds of rock garden plants and other hardy perennials can be sown this month.
Cuttings also propagate rock garden plants from the young shoots that sprouted after flowering ceased. These are rooted in moist sand. All sorts of flowering shrubs can be rooted from cuttings, too.
You can also root cuttings of English ivies and red salvia. The latter make good house plants when potted up.
Zinnias and calendulas will flower from late August until frost if their seed is sown from July 1 to 10.
Reducing Sunlight Exposure
Whatever the project intended for the cold frame, the intensity of sunlight which enters it in summer must be reduced. This is the reverse of what is done in spring when we invite the sun’s heat and light. Therefore, shade the glass as shown in the drawings below.
If you are planning extra cold frame space, consider a temporary frame made from one of the glass substitutes.
Screen-glass answers the purpose very well. It can be cut with shears to any length and attached to 1” x 2” inch lumber strips. Extra shading is not needed as the material is not glass-clear. Besides, it gives a certain amount of heat insulation.
Sowing Seeds
If you plan to sow seeds, the soil must be renewed to a depth of 3” inches. A mixture of equal parts of loam, sand, and peat moss or humus is best. Put it through a 14” inch screen, spread it over the area, and tamp it fairly firmly.
Seeds are sown as advised for spring operations. After sowing, water with a fine hose, then replace the shaded sash but allow an opening of an inch or two for air.
A daily examination is needed to moisten any dry spots. The shaded sash will admit sufficient light for the seedlings until the pricking-off or transplanting period. At this time, the seedlings should be gradually exposed to full sunlight before pricking off.
It’s too early to start pansies, daisies, forget-me-nots, and similar plants usually started in late summer. But Canterbury bells, foxglove, hollyhocks, sweet William, columbine, delphinium, pyrethrum, and numerous other hardy perennials are started now.
Rock garden plants started now are arabis, aubrieta, alyssum, snow-rn-summer, dianthus, thyme, tunica, and silene.
44659 by P. J. Mckenna